Oliver Gutfleisch IFW Dresden
Karl G. Sandeman Imperial College London
Aru Yan Chinese Academy of Sciences
Asaya Fujita Tohoku University
Karl Gschneidner Iowa State University
FF1: Magneto Calorics and Magnetic Cooling I
Monday PM, November 29, 2010
Republic A (Sheraton)
9:30 AM - **FF1.1
Advanced Magnetocaloric Materials.
Vitalij Pecharsky 1 2 , K. Gschneider 1 2 Show Abstract
1 , Ames Laboratory, Ames, Iowa, United States, 2 Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
The discovery of the giant magnetocaloric effect in Gd5Si2Ge2 and other R5T4 compounds (R = rare earth metal and T is a Group 14 element) generated a broad interest in the magnetocaloric effect and magnetostructural transitions. Reports on the giant magnetocaloric effect in other systems soon followed. These include MnFePxAs1-x and related compounds, La(Fe1-xSix)13 and their hydrides, Mn(AsxSb1-x), CoMnSixGe1-x, and Ni2MnGa and some closely related Heusler phases. A common feature is the enhancement of the magnetic entropy effect by the overlapping contribution from the lattice, regardless whether it is a massive structural change like in R5T4 compounds, or only a phase volume change as in La(Fe1-xSix)13. Both the magnetic and lattice entropies are, therefore, important and each contribution must be maximized in order to have the optimum magnetocaloric effect. Both of these entropy terms and the potential pathways towards a further enhancement of the giant magnetocaloric effect will be discussed.This work is supported by the U.S. Department of Energy – Basic Energy Sciences under contract No. DE-AC02-07CH11358.
10:00 AM - **FF1.2
Rare Earth Raw Materials for Magnetic Refrigeration.
Jiaohong Huang 1 2 , Yan Wang 1 , Hongwei Yan 1 Show Abstract
1 , Baotou Research Institute of Rare Earths, Baotou, Inner Mongolia, China, 2 , National Engineering Research Centre of Rare Earth Metallurgy and Function Materials, Baotou, IInner Mongolia, China
Rare Earth metals are the most important and indispensable materials for research and development of magnetic refrigeration materials with gaint magnetocaloric effect at room temperature.. Many magnetic refrigeration materials, such as Gd, Gd-Tb, Gd-Dy, Gd5Si2Ge2 and La(FeSi)13, contain rare earth elements. Especially, the magentic field based on NdFeB permanent magnets is the most applied magnetic field source. Hence, that is to say, magnetic refrigeration technology at room temperature can not develop without rare earth elements. This paper introduces the magnetic properties of rare earth elements, magnetocaloric effect of some rare earth elements and alloys, the magnetic field based on NdFeB, the reservation and exploitations of rare earths in different nations, the production status of rare earth elements such as La, Pr, Nd, Gd, Tb, Dr and Er that are used in magnetic refrigeration, and the present situation of Chinese rare earth industry and so on.
10:30 AM - **FF1.3
Magnetic Refrigeration Technology using Magnetocaloric Materials and Their Applications.
A. Saito 1 , S. Kaji 1 , T. Kobayashi 1 Show Abstract
1 Corporate Research and Development Center, Toshiba Corporation, Kawasaki Japan
Recent development of the magnetocaloric materials and prototype equipment for magnetic refrigeration technology has attracted much attention as new avenue for the cooling technology of preventing the global warming. However, in order to put the magnetic refrigeration technology into practical use, there are many challenges still exist, both development of equipment and systems and that of magnetocaloric materials. In this paper, we present a research of room temperature magnetic refrigeration using permanent magnets and a thermal cycle of the active magnetic regenerative (AMR) refrigeration. The lowest achieving temperature of minus 10 degrees C and the maximum temperature span of 46 degrees C were obtained by operating the AMR cycle with Gd-alloy spheres as the magnetic refrigerant. The cooling performance depends on many factors such as conditions of a cycle operation and the magnetocaloric materials performance. As for magnetocaloric materials, the entropy change triggered by external magnetic field is definitely important, but the value of specific heat and thermal conductivity are also important factors. The adiabatic temperature change of magnetocaloric materials is determined by the magnetic entropy change and its specific heat, then, the balance between magnetic contribution and lattice contribution to the specific heat near magnetic phase transition temperature controls the materials performance. On the other hand, the required cooling performance is quite different for each application target such as household refrigerator, air-conditioner, industrial freezer and cold storage. Therefore, optimum design and addressing the technical issues toward practical use of magnetic refrigeration technology are required.This work was partially supported financially by the Japan Science and Technology Agency, and now is partially supported by New Energy Development Organization.
11:00 AM - FF1: MCE
11:30 AM - **FF1.4
Magnetocaloric Properties Desired for Magnetic Refrigeration System Near Room Temperature.
Hirofumi Wada 1 Show Abstract
1 Department of Physics, Kyushu University, Fukuoka Japan
Discovery of giant magnetocaloric effects near room temperature has opened the door to the next evolution of magnetic refrigeration. In the last several years, we have been involved in a national project of “Development on Room Temperature Magnetic Refrigeration” in Japan. The final purpose of this project is to develop the 100 W class magnetic refrigeration system with COP > 3. For the practical application, however, the COP > 7.5 is strongly required. This means that we have to find new magnetic refrigerant materials of which cooling capacity is more than 2.5 times higher than that of Gd. In this presentation, we will discuss the required magnetocaloric properties of magnetic refrigerant materials for COP = 7.5. First, we assume that the magnetic refrigeration system works in the temperature span of 30 K near room temperature. It is known that giant magnetocaloric materials exhibit very large entropy changes but their temperature span is narrow. Therefore, we have to use the composite materials with different Curie temperatures to cover the desired temperature range. Second, the maximum magnetic field of the magnetic refrigerator is assumed to be 1.4 T. It should be noted that the cooling capacity of giant magnetocaloric systems is proportional to a magnetic field, while that of Gd shows a nonlinear change with a magnetic field. Based on the results of Gd, we evaluated the required entropy change for COP = 7.5 as a function of temperature. We also examined the entropy change of Mn2-xFexP0.8Ge0.2 and La(FeCoSi)13. It is found that the former system would satisfy the above criteria for COP = 7.5, if the optimum combination of materials is selected.
12:00 PM - FF1.5
Magnetocaloric Effects in Mn-based Metamagnets.
Zsolt Gercsi 1 , Karl Sandeman 1 Show Abstract
1 Physics Department, Imperial College, London United Kingdom
The magnetocaloric effect (MCE) is the change of temperature of a material in a changing magnetic field, and was first observed in iron by Warburg. It has until now been exploited in paramagnetic salts as a means of cooling below the temperature of liquid Helium. However, the high global warming potential of conventional HFC refrigerants and the large fraction of energy used for cooling are concerns that currently fuel interest in such "magnetic cooling" as a high-efficiency solid-state method of refrigeration close to room temperature. Most candidate room temperature magnetic refrigerants materials are ferromagnets, often containing manganese (MnAs, MnFe(As,P), CoMnGe). However, metamagnets such as CoMnSi that have a complex non-collinear magnetic structure can also exhibit large MCEs. We have recently shown that in CoMnSi , there is a large and opposing change in the two shortest Mn-Mn distances, of around 2% with the increase of temperature. This change brings about an Invar-like effect in sample volume in zero magnetic field and it also couples strongly to the suppression of helimagnetism in finite magnetic fields and brings about a tricritical point, with enhanced magnetocaloric and magnetostrictive effects.What is common to many of these Mn-containing materials, both ferromagnetic and metamagnetic, is the orthorhombic (Pnma,62) structure in which they form. Our new experimental findings shed light on the criticality of the closest Mn-Mn separations in such MnP-type structures. We therefore investigated the structural conditions for metamagnetism in MnP and related materials using Density Functional Theory. We found that a particular Mn-Mn separation plays the dominant role in determining the change from antiferromagnetic to ferromagnetic order in such systems and an excellent correlation between our calculations and structural and magnetic data from the literature is established . Based on our calculations it should be possible to find new Mn-containing alloys that possess field-induced metamagnetism and associated magnetocaloric effects. The research leading to these results has received funding from the European Community’s 7th Framework Programme under grant agreement No. 214864. “Giant magneto-elastic coupling in a metallic helical metamagnet”A. Barcza, Z. Gercsi, K.S. Knight, K.G. SandemanPhys. Rev. Lett. 104, 247202 (2010) “Structurally driven metamagnetism in MnP and related Pnma compounds”Z. Gercsi and K.G. SandemanPhys. Rev. B 81, 224426 (2010)
12:15 PM - FF1.6
Magnetic Refrigeration with GdN by Active Magnetic Refrigerator Cycle.
Yusuke Hirayama 1 , Hiroyuki Okada 1 , Takashi Nakagawa 1 , Takao Yamamoto 1 , Takafumi Kusunose 2 , Takenori Numazawa 3 , Koichi Matsumoto 4 , Toshio Irie 5 , Eiji Nakamura 5 Show Abstract
1 Department of Management of Industry and Technology, Osaka University, Osaka Japan, 2 Department of Advanced Materials Science, Kagawa university , Kagawa Japan, 3 Exploratory Materials Research Laboratories for Energy and Environment, National Institute for Materials Science, Tsukuba Japan, 4 Department of Physics, Kanazawa University, Kanazawa Japan, 5 , SANTOKU corporation, Kobe Japan
Mononitrides of rare earth elements, Gd, Tb, Dy, Ho, Er, and their binary nitrides are ferromagnets with Curie temperatures, TC, in a range between 4 ~ 65 K, accompanied by a large magnetic entropy change ΔS around each TC[1,2]. In addition, these nitrides do not react with H2 gas. We have pointed out that they are promising candidate materials for magnetic refrigeration systems for cooling and liquefying hydrogen from liquid nitrogen temperature (77 → 20 K). In this paper, we report on a refrigeration experiment performed in the temperature range 48 ~ 66 K.The spherical GdN material was synthesized from spherical Gd metal (φ: 0.85 ~ 1.0 mm, 99.9 % purity) in a hot isostatic pressing equipment (O2-Dr. HIP; Kobelco Co., Ltd.) operated at 1873 K in 200 MPa-N2 gas of 99.9999 % purity for 2 hours. These conditions allowed Gd metal to transform into GdN without any crack of the sphere material. Occurring phase was confirmed as GdN by the XRD technique and its magnetization and specific heat, CH, were measured with a PPMS (Quantum Design, Inc.) under different fields (0 ~ 7.0 T). Adiabatic temperature change ΔTad was calculated from the CH –T curve. The refrigeration apparatus used in this work follows an AMR (active magnetic regenerator) cycle by driving a regenerator bed filled with the spherical GdN and He gas as a transfer fluid separately along a field gradient in a 4–T super conducting magnet. Temperatures at the upper and lower sides of the bed were monitored. The bed and gas were confined in a cylinder which was thermally insulated. The cycle was started after the cylinder attained at a thermal equilibrium by using a GM refrigerator and heaters attached on it and the temperature gradient was produced in the bed. The steady state in which the temperature span ΔTspan (=ΔTupper – ΔTlower) became constant was attained in 150sec. ΔTspan was 4.7 ~ 5.1 degree under the steady state and exhibited a slight but significant temperature dependence with a broad peak at 63 K which was near the Curie temperature of GdN, 65 K. Then obtained ΔTspan was 1.5 times as large as ΔTad, which indicated that the AMR cycle exploited the magnetic properties of GdN. T. Nakagawa et al., J. Alloys & Compounds, Vol. 408-412 (2006) 187-190. Y. Hirayama et al., Mater. Res. Soc. Symp. Proc., (2007) 1040E-Q09-05. Y. Hirayama et al., IEEE Trans. Magnetics, VOL. 44, NO. 11, 2008.
FF2: Magneto Calorics and Magnetic Cooling II
Monday PM, November 29, 2010
Republic A (Sheraton)
3:00 PM - **FF2.1
Powder Metallurgical Synthesis of La-Fe-Co-Si Parts for Magnetic Refrigeration.
Matthias Katter 1 , Volker Zellmann 1 , Alexander Barcza 1 Show Abstract
1 , Vacuumschmelze GmbH & Co. KG, Hanau Germany
An industrially up-scalable production route for La-Fe-Co-Si parts for the application in magnetocaloric heat exchangers based on powder metallurgy was developed. Similar to the well-established production route of sintered Nd-Fe-B magnets, various La-Fe-Co-Si precursor alloys are milled to a fine powder with a mean particle size of less than 10 µm and blended to meet the required compositions. The powders are then compacted by die pressing or isostatic pressing to green compacts and sintered at about 1100°C to achieve a density of about 7.2 g/cm3. During the sintering treatment the magnetocalorically active La(Fe,Co,Si)13 phase is formed out of the powder constituents. By varying the Co content, the Curie temperature can be tuned to the commercial relevant range from -20 to + 60°C . In this state the material is difficult to machine because of the large magnetovolume effect of the La(Fe,Co,Si)13 phase at the Curie temperature which leads to the formation of cracks. During a heat treatment at about 800°C the 1:13 phase is decomposed into a fine mixture of α-Fe and other La- and Si-rich phases . In this state the material can be machined by grinding and cutting into both thin plates and even monolithic sliced blocks necessary for magnetocaloric heat exchangers. Finally, the magnetocalorically active 1:13 phase is recombined by a heat treatment at about 1050°C. In the final state the amount of remaining α-Fe can be reduced to < 5%. This thermally induced decomposition and recombination (TDR) process is fully reversible and allows the industrially up-scalable production of shaped parts for magnetic refrigeration.The research leading to these results has received funding from the European Community’s 7th Framework Programme under grant agreement No. 214864. M. Katter, V. Zellmann, G.W. Reppel, K. Uestuener, IEEE Trans. Magn. 44 (2008) 3044. M. Katter, V. Zellmann, G.W. Reppel, K. Uestuener, Proc. 3rd IIF-IIR Int. Conf. on Magnetic Refrigeration at Room Temperature, Des Moines, USA (2009) 83.
3:30 PM - **FF2.2
Adiabatic Temperature Change and Magneto-volume Effect in La-Fe-Si bulk, Melt-spun and Hydrogenated Compounds.
Konstantin Skokov 1 , Jian Liu 1 , Maria Krautz 1 , Oliver Gutfleisch 1 Show Abstract
1 Institute for Metallic Materials, Leibniz Institute for Solid State and Materials Research, Dresden Germany
In recent years, the interest in energy-saving technologies and related materials has noticeably increased. The technology of near-room temperature magnetic refrigeration belongs to them, and compounds with the first-order type ferromagnetic-paramagnetic transition are of great interest for magnetic cooling. As a general rule, such compounds should have a high value of the magnetic entropy change, which is fulfilled in the giant magnetocaloric system LaFe13-xSix. In addition, the high content of iron in LaFe13-xSix makes it a much cheaper alternative to the rare-earth metal Gd that is often used in magnetic refrigeration demonstrators.The most reliable method for determining magnetocaloric properties is direct measurement of adiabatic temperature change ΔTad. This can supply important information on the dynamics of thermo-magnetic processes and on magnetic hysteresis caused by the field-induced magnetic transition. At the same time in first-order type transitions, it is possible to get various anomalies in the temperature dependence of lattice parameters, which leads to an additional contribution to the magnetocaloric effect. In LaFe13-xSix there is an isotropic volume expansion ΔVad near the Curie temperature by an application of magnetic field (magneto-volume effect). In this talk, we provide a comparative research of the field dependences ΔTad(H) and ΔVad(H) on bulk and melt-spun LaFe13-xSix. We studied dynamics, magnetic and temperature hystereses, and cycling effects during the first-order transition.The melt-spinning method is both quick and low cost, and negates the usual objections to practical implementation of La-Fe-Si as a refrigerant. This method reduces the presence of a parasitic α-Fe second phase, which does not contribute to the MCE. In the case of a melt-spun precursor, only several hours of annealing is necessary in comparison to one-week annealing for bulk alloy. In the last part, we present the hydrogenation behaviours of La-Fe-Si alloys. Curie temperature of La-Fe-Si alloys can be shifted from 180 K to 330 K by hydrogen absorption. Such adjustability by atomic scale manipulation is a great asset when designing a magnetocaloric material for room-temperature application. More importantly, the first-order transition feature can be remained in the La-Fe-Si-H alloys, unlike the case that the substitution of Fe by Co or Si generally provides an evolution towards second-order behaviour and thus the reduced ΔTad.
4:30 PM - FF2.3
Magnetic, Electrical and Inverse Magnetocaloric Effects in Co and Fe Doped Ni-Mn-Ga Heusler Alloys.
Arjun Pathak 1 , Igor Dubenko 1 , Shane Stadler 2 , Naushad Ali 1 Show Abstract
1 Physics, Southern Illinois University Carbondale, Carbondale, Illinois, United States, 2 Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana, United States
The off-stoichiometric Ni2Mn1+yX1-y (X=In, Sb, Sn, Ga) Heusler alloys that undergo martensitic transformations at TM below the ferromagnetic ordering temperature (TC) have attracted attention because of their unique and diverse physical properties such as the giant magnetocaloric effect (MCE) and, therefore, their possible employment as working materials in environmentally friendly magnetic refrigerators [1, 2]. In some cases, the magnetization of the martensitic phase of these compounds is considerably smaller than that of the austenite phase, resulting in an inverse (i.e., positive) magnetic entropy change (ΔSM) at the martensitic transition temperature, TM . Unlike the Ni-Mn-In/Sn/Sb systems, the martensitic and austenitic phases of Ni2MnGa are both ferromagnetic, and characterized by a small difference in magnetization (ΔM) between the two phases. Stoichiometric Ni2MnGa is a typical ferromagnetic shape memory alloy (FSMA) that passes from a low-symmetry, ferromagnetic martensitic phase to a ferromagnetic austenitic phase at the martensitic transition temperature (TM=202 K), and transforms to a paramagnetic state above the Curie temperature (TC=376 K) . Recently, it has been shown that changing the composition of the Ga–based Heusler alloys can also result in a significant difference between the magnetizations of the austenitic and martensitic phases, and in field-induced reverse martensitic transformations [4-6]. Therefore, large magnetoresistance (MR) and MCE can also be expected to be observed in Ga-based Heusler alloys. In this study, we will present the magnetic, electrical, and inverse magnetocaloric properties through magnetization and resistivity measurements in recently discovered Co and Fe doped Ni-Mn-Ga Heusler alloys. We observed field-induced, inverse martensitic transformations, large differences in magnetization between austenitic and martensitic phases (ΔM), significantly large inverse MCE’s, and large magnetoresistance. The systems are also uniquely characterized by small hysteresis effects for optimum choices of compositions. Magnetic phase diagrams will be presented and described in terms of the valence electron concentration, the degree of tetragonal distortion, and the average metallic radii.References:. A. K. Pathak et al, Appl. Phys. Lett. 90, 262504 (2007). X. Zhang et al, Phys. Rev. B 76, 132403 (2007). A. N. Vasil’ev et al, Phy. Rev. B 59, 1113 (1999). S. Fabbrici et al, Appl. Phys. Lett. 95, 022508 (2009). C. Jiang et al, Appl. Phys. Lett. 95, 012501 (2009). S. Y. Yu et al, Appl. Phys. Lett. 91, 102507 (2007).Acknowledgments: This research was support by the Research Opportunity Award from Research Corporation (RA-0357) and by the Office of Basic Energy Sciences, Material Sciences Division of the U. S. Department of Energy (Contact No. DE-FGP2-06ER46291).
4:45 PM - FF2.4
The Giant Magnetocaloric Effect in Ni-Co-Mn-Sn Heusler Alloys.
Raju Ramanujan 1 , Boon Hwee Tan 1 , X. Chen 1 Show Abstract
1 , Nanyang Tech. Univ., Singapore Singapore
Affordable near room temperature magnetic cooling materials can be developed by utilizing the giant inverse magnetocaloric effect (GMCE) observed in Ni-Mn-X (X=Sn, In, Ga, and Sb) Heusler alloys. Of great current interest is the GMCE observed in Ni50Mn50-xSnx (x=6-20) alloys, this GMCE is a result of magneto-structural phase transformations. Such transformations are highly sensitive to composition, hence the influence of composition on the magnetocaloric effect was studied by TEM, DSC and magnetometry, it was found that the martensitic transition is much more sensitive to composition than the magnetic transition. A large variation in maximum entropy change was observed due to differences in the transition temperatures and the plate shaped martensite microstructure. To increase refrigeration capacity (RC) and operating temperature span, melt spun Co alloyed Ni-Mn-Sn ribbons were studied, the martensitic transition temperature and Curie temperature of the austenite phase were tuned to higher temperatures without decreasing maximum entropy change. Therefore, the operating temperature span and RC of Ni-Mn-Sn-Co alloys can be increased by Co additions. Multilayered magnetic regenerators can be developed by arranging such alloys with different working temperatures in a laminar layout. A lab scale magnetic cooling system constructed to test such magnetocaloric materials will be described. This active magnetic regenerator refrigerator consists of permanent magnet, active magnetic refrigeration (AMR) cycle bed, pumps, hydraulic circuit, active magnetic double regenerator cycle and control subsystems. The magnetic field is supplied by Nd-Fe-B permanent magnets. The AMR bed made of stainless steel 304 encloses the magnetocaloric working substance. The refrigerator is controlled by a programmable controller and heat exchangers are employed to expel heat. This refrigerator employs standard components for hardware, is low cost and easy to produce. Results obtained using this system will also be presented.
5:00 PM - **FF2.5
Magnetocaloric Material Architectures.
Lesley Cohen 1 Show Abstract
1 Blackett Laboratory, Imperial College London, London United Kingdom
The “giant magnetocaloric” magnetic materials, which undergo a phase transition from one form of magnetic order to another with an associated “giant” change of entropy have attracted world wide interest since the seminal paper of Pecharsky & Gschneidner, in 1997. In this talk I will in part review what we understand to be important for giant magnetocalorics namely entropy change, order of the transition, tunability, dynamics and hysteresis. Over recent years a handful of compounds have been identified as the most promising contenders for refrigeration application. Understanding the nature of the transition in these systems and how to optimise them to maximise the associated entropy and adiabatic temperature change is an area of vital importance and of current widespread study. At Imperial College we have developed a number of novel characterisation probes that enable study of the magnetic transition process (scanning Hall probe imaging) and separation of latent heat and heat capacity. The probes provide unique insight into the nature of the magnetocaloric transition. I will consider one or two example systems and discuss our current understanding of their properties and possible future directions.
5:30 PM - FF2.6
Giant Magnetocaloric Effects in La0.8Ce0.2Fe11.4-x(Cr or Ni)xSi1.6 Compounds.
Shandong Li 1 2 , Zhiping Lin 1 , Zongjun Tian 3 , Feng Xu 4 , Yanmin Yang 1 , Jianpeng Wu 1 , Yi Hu 1 , Xinle Cai 1 , Nian X. Sun 2 Show Abstract
1 Department of Physics, Fujian Normal University, Fuzhou, Fujian, China, 2 Electrical and Computer Engineering Department, Northeastern University, Boston, Massachusetts, United States, 3 College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu, China, 4 Department of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu, China
The magnetic transition and magnetocaloric effect of La0.8Ce0.2Fe11.4-xMxSi1.6 (x=0.0-0.4) compounds were investigated with the M being Cr and Ni, which are located at the left and right side of Fe in the periodic table of elements. Cr-doping gave rise to a reduction of Curie temperature (TC) of the compounds, while Ni-doping led to an increase of Tc, indicating the 3d electron concentration plays an important role in the magnetic transition of the La0.8Ce0.2Fe11.4-xMxSi1.6 alloys. A giant magnetic entropy change up to 106 J/kg.K under field of 0 - 2 T, and a huge refrigeration capacity up to 335.6 J/kg were observed in the La0.8Ce0.2Fe11.3Cr0.2Si1.6 compounds, which is close to that for gas refrigerant. The ΔSM of Ni-doped compounds was dramatically decreased, which was associated with a gradual change in the magnetic phase transition from the first-order transition (for Ni x<0.3) to the second-order one (for Ni x>0.3).
FF3: Poster Session: Magneto Calorics and Magnetic Cooling III
Tuesday AM, November 30, 2010
Exhibition Hall D (Hynes)
9:00 PM - FF3.1
The Hydrogenation Behabiors of LaFe13-xSix (x=1.4 and 1.56) Compounds.
Tang Yongbai 1 , Chen Yungui 1 , Wang Jinwei 1 , Chen Xiang 1 Show Abstract
1 , Sichuan University, Chengdu China
The hydrogen absorption kinetics and hydrogen desorption PCT(Pressure-Capability-Temperature) performance of LaFe13-xSix(x=1.4 and 1.56) compounds were investigated in this paper. The results show that the hydrogen absorption of these compounds can be saturated within about one hour at near room temperature after they were activated twice at 673 K. It was found from the hydrogen desorption PCT curves at 0-4.5 bar and 273 K-353 K that no hydrogen desorption plateau existed in these compounds and hydrogen capacity of these compounds could be easily adjusted by changing testing temperature or pressure. On the other hand, the thermal gravimetric test results of LaFe13-xSix hydrides show that the hydrogen desorption of them increases obviously above about 448 K and ends up to about 650 K. Finally, the results of XRD analysis indicated the NaZn13-type main structure of LaFe13-xSix compounds was stable during the cycle of hydrogen absorption and desorption.
9:00 PM - FF3.10
Magnetocaloric Effect in Ribbon Samples of Heusler Alloys Ni - Fe - Mn - Ga.
Akhmed Aliev 1 , Akhmed Batdalov 1 , Ibragimkhan Kamilov 1 , Victor Koledov 2 , Vladimir Shavrov 2 , Blanca Hernando 3 , Victor Prida 3 Show Abstract
1 , Amirkhanov Institute of Physycs of Daghestan Scientific Center, RAS, Makhachkala Russian Federation, 2 , Kotelnikov Institute of Radio Engineering and Electronics, RAS, Moscow Russian Federation, 3 , 3Depto. de Física, Facultad de Ciencias, Universidad de Oviedo, Oviedo Spain
The direct measurements of the magnetocaloric effect in samples of rapidly quenched ribbons of Heusler alloys Ni2.15Fe0.06Mn0.79Ga and Ni2.0Fe0.01Mn0.79Ga with potential applications in magnetic refrigeration technology are carried out. The measurements were made by precise method based on the measuring of the amplitude of the oscillation of the sample temperature in the alternating magnetic field. In the studied compositions direct and inverse magnetocaloric effects associated with magnetic (paramagnet - ferromagnet - antiferromagnet) and structural (austenite - martensite) phase transitions are found.
9:00 PM - FF3.11
Monte Carlo Simulations of the Exchange Bias Effect in Heusler Ni-Mn-Sb Alloys Using Real Unit Cell.
Vasiliy Buchelnikov 1 , Vladimir Sokolovskiy 1 , Ivan Taranenko 1 , Peter Entel 2 , Sergey Taskaev 1 Show Abstract
1 , Chelyabinsk State University, Chelyabinsk Russian Federation, 2 , University of Duisburg-Essen, Duisburg Germany
Ferromagnetic (FM) Heusler Ni-Mn-X (X= In, Sn, Sb) alloys have unique properties such as a shape memory effect, a giant magnetoresistence and magnetocaloric effect, and exchange bias effect . The reason of these properties is a coupled metamagnetostructural phase transition. Heusler alloys can be used in various technological areas such as a medicine, an aircraft, a magnetic cooling technology. Recent experiments of non-stoichiometric Ni50Mn25+xX25-x (X=In, Sn, Sb) have shown that in the martensitic state the excess of Mn2 atoms occupying the X sublattice sites (X=In, Sn, Sb) interact with Mn1 atoms on the Mn sublattice sites antiferromagnetically (AFM). Opposite, the interaction between Mn1 atoms on the regular Mn sublattice sites is FM. In the case of the austenitic state the interactions atoms (Mn1-Mn2, Mn2-Mn2 and Mn1-Mn1) between all Mn atoms are FM .In this work, we present a theoretical model for investigation of the exchange bias effect in Heusler Ni50Mn25+xSb25-x alloys by Monte Carlo method. In the proposed model we use a cubic lattice with real unit cell of Heusler alloys and with periodic boundary conditions. The unit cell arises from four interpenetrating fcc sublattices with atoms Sb, Mn and Ni, at locations (0, 0, 0), (½, ½, ½), (¼, ¼, ¼, ¼) and (¾, ¾, ¾), respectively. For non-stoichiometric compositions the excess of Mn2 atoms are located at Sb’s crystallographic sites and a configuration of these atoms is set randomly. The whole lattice consists of magnetic atoms (Mn and Ni) and non-magnetic (Sb) ones. Recent ab initio simulations have shown that Mn1-Mn1, Mn1-Ni, Mn2-Mn2, and Mn2-Ni interactions are FM, while Mn1-Mn2 interaction is AFM, moreover Mn-Ni interactions are the largest for non-stoichiometric compounds . In our work, we take into account magnetic interactions using ab initio exchange constants only in three coordination spheres. The model Hamiltonian includes FM and AFM Heisenberg’s spin interactions with an anisotropy term and an external magnetic field. Our simulations have shown that the exchange bias field depends on a concentration of AFM atoms, a temperature and number of hysteresis loops. Moreover the value of bias field decreases with increasing temperature, and for Ni50Mn37.5Sb12.5 alloy we have found a temperature of blocking exchange bias effect. Theoretical blocking temperature is closer to experimental value . 1. A. Planes et al., J. Phys.: Condens. Matter 21, 233201 (2009).2. H. Herper, M. Gruner, A. Hutch, and P. Entel (unpublished work, 2010).3. M. Khan et al., Appl. Phys. Lett. 91, 072510 (2007).
9:00 PM - FF3.12
Exploring the Free Energy of Mn0.985Fe0.015As: Magnetocaloric Effects and Their Relation to Metastable Initial States.
M. Bratko 1 , K. Morrison 1 , A. de Campos 2 , S. Gama 3 , K. Sandeman 1 , L. Cohen 1 Show Abstract
1 Physics Department, Imperial College London, London United Kingdom, 2 Instituto de Ciência Tecnologia e Exatas, Universidade Federal do Triângulo Mineiro, Uberaba, MG, Brazil, 3 Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, Diadema, SP, Brazil
Most measurements of magnetocaloric effects (MCEs) are indirect and typically use isothermal magnetisation data to obtain an estimate of magnetic field-induced isothermal entropy change. The resulting entropy changes are typically of the order of 1-20 JK-1kg-1 but so-called "colossal" MCEs have also been reported, with peak entropy changes that are 10 times higher, e.g. in MnAs-based compounds . Recent work has demonstrated that the isothermal difference between the entropy of states that are in stable equilibrium is in fact not colossal in these systems [2,3,4]. However, direct measurements of the isothermal entropy change from a metastable (supercooled or superheated) starting point have until now not been made.Here we deduce the magnetic field-induced entropy change associated with the first order Curie transition of Mn0.985Fe0.015As. We make both indirect measurements derived from magnetisation and direct measurements, which use a novel calorimetric technique where magnetic field is applied and latent heat and a.c. heat capacity are measured. We study two magnetisation histories in detail. In the first the material is reset to the paramagnetic state by heating before every re-magnetisation. In the second magnetic and calorimetric data are taken at various temperatures without resetting the material to the paramagnetic state. Only the latter approach results in an apparent collosal peak in entropy change, when deduced using the indirect method. By comparison, the direct measurement shows only a small difference between the magnitude of the magnetocaloric effect arising from either field history. We therefore conclude that there is no significant entropic benefit to be gained from starting from a metastable point. In agreement with theoretical work , the apparent colossal MCE results only when the Maxwell relation is applied to magnetisation data of inequivalent magnetic history in the hysteretic (transition) region. A. de Campos et al., Nature Materials 5, 802 (2006).  L. Tocado et al., J. Appl. Phys. 105, 093918 (2009). L. Caron et al., J. Magn. Magn. Mat. 321, 3559 (2009). J.S. Amaral and V.S. Amaral, Appl. Phys. Lett. 94, 042506 (2009).
9:00 PM - FF3.13
A Global Solution to the Magnetic Entropy Overestimation by Maxwell Relation in the Mixed Phase State: A Case Study with Doped MnAs.
Soma Das 1 , Joao Amaral 1 2 , Vitor Amaral 1 Show Abstract
1 Departamento de Física and CICECO, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro Portugal, 2 IFIMUP-IN and Departamento de Física e Astronomia da Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto Portugal
The recent magnetocaloric research on the first order phase transition materials revealed that the use of Maxwell’s relation to predict magnetic entropy behavior near the Curie temperature of the material can generate erroneous result because of the non-equilibrium experimental conditions coming mainly from the metamagnetic transition of the system [1-6] that generally disagree with entropy from calorimetric experiments. It was shown that  for a system with first order magnetic phase transition, especially in the mixed phase state, the usual data analysis procedure can give anomalous peak of magnetic entropy change that may sometimes exceed the theoretical limit. Here, we are giving a global solution to this problem of magnetic entropy overestimation in case of first order phase transition materials with mixed phase state by modeling the magnetization as a weighted summation of the contributions from each of the magnetic phases present and their relative change with respect to temperature and magnetic field. This allowed us to obtain realistic entropy change values . In this presentation, we are showing the magnetic entropy and its correction for polycrystalline MnAs; a typical 1st order phase transition system, doped with 2% Cu and Cr to get different field and temperature dependent thermodynamic behavior near phase transition. Our results demonstrated a well-defined correlation between the mixed-phase state thermal kinetics and high entropy values obtained from Maxwell’s relation for these doped MnAs systems, confirming the postulates of our modeling. Although the doping apparently seemed to vary the entropy maximum depending on the relative proportion of Cu and Cr, the real magnetic entropy after correction showed nearly similar value. The doping induced tuning is actually obtained in the working temperature span of the material with a steady RCP value. In particular, we can say that an extended working temperature zone shifted at comparatively lower temperature is obtained with higher Cr doping where Cu only influences mostly the mixed phase dynamics.  A. Giguere, M. Foldeaki, B. Ravi Gopal, R. Chahine, T. K. Bose, A. Frydman and J. A. Barclay, Phys Rev Lett 83, 2262 (1999)V. K. Pecharsky and K. A. Gschneidner, Jr., J. Appl. Phys. 86, 6315 (1999)G. J. Liu, J. R. Sun, J. Shen, B. Guo, H. W. Zhang, F. X. Hu, and B. G. Shen, Appl. Phys. Lett. 90, 032507 (2007)J. S. Amaral and V. S. Amaral, Appl. Phys. Lett. 94, 042506 (2009)L. Tocado, E. Palacios, and R. Burriel, J. Appl. Phys. 105, 093918 (2009) S. Das, J. S. Amaral, and V. S. Amaral, J Phys. D: Appl. Phys. FTC 43, 152002 (2010)
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Magnetoelastic Phase Transitions under Hydrostatic Pressure.
Luana Caron 1 , N. Trung 1 , Bastian Knoors 1 , Merien Uitterhoeve 1 , ZhiQiang Ou 1 , N. Dung 1 , Ekkes Bruck 1 Show Abstract
1 , TUDelft, Delft Netherlands
Solid state cooling technology as alternative to gas compression is being studied for years. Research on the magnetocaloric effect has flourished due to the observation of high entropy changes around a variety of first order magnetic phase transitions. More than that, the discovery of materials in which the phase transition can be tuned through chemical substitutions to temperatures around and above room temperature made commercial prototypes feasible and competitive.Fe2P based compounds, such as FeMnP1-xAsx, are rather attractive due to their low cost and good magnetocaloric properties. In these compounds both thermal hysteresis and TC can be easily tuned by composition, often pushing the system to the border between 1st and 2nd order phase transitions.Recently, we were able to successfully substitute, partially or completely, the As by Si, Ge or a combination of both elements, while retaining the good magnetocaloric properties and tunability presented by the Fe2P based compounds, such as FeMnP1-xAsx compounds.In particular, Ge substituted samples present entropy changes as high as 20 J/kgK for a 2 T magnetic field change and remarkably small thermal hysteresis. Even more remarkable are the results from magnetization measurements under hydrostatic pressure. Pressure has no or very little effect on the Curie temperature of the samples over certain compositional ranges. This is an unexpected behavior for first order magnetic phase transitions since they should intrinsically display a discontinuous volume change.Here we report on pressure and temperature dependent X-rays diffraction that finally confirm the absence of a volume change due to the transition at the Curie temperature. However we observe distinct changes on c/a in the hexagonal system which conserve the discontinuity of the lattice parameters and correlate directly with TC.These results strongly suggest that thermal hysteresis is related with volume change rather than with the discontinuity in lattice parameters. For high frequency applications using magnetocaloric materials, low thermal hysteresis is a key feature and the absence of volume change is desirable, since it brings further stability. Our results may serve as a guideline for the search of new magnetocaloric materials for such applications. 1. Tegus, O., Bruck, E., Buschow, K.H.J. & de Boer, F.R. Transition-metal-based magnetic refrigerants for room-temperature applications. Nature 415, 150-152 (2002). Trung, N.T. et al. Tunable thermal hysteresis in MnFe(P,Ge) compounds. Appl. Phys. Lett. 94, 102513-3(2009)
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Direct Measurement of the Isothermal Entropy Change in Mn3GaC1-x.
Elias Palacios 0 , Saeid Elkatlawy 0 , GaoFeng Wang 0 , Ramon Burriel 0 Show Abstract
0 , Instituto de Ciencia de Materiales de Aragon, Zaragoza Spain
The magnetocaloric effect (MCE) is enhanced in some materials in which the isothermal application of an external magnetic field produces a change of the electronic entropy, not merely the magnetic entropy. Among them Mn3
GaC is a nice test case, since the external field induces a first-order transition below Tt1
≈ 170 K (for H
= 0) from an antiferromagnetic phase (AF) to a ferromagnetic one (F). The Curie temperature TC
= 242 K is quite higher than Tt1
, therefore the magnetic entropy of both phases is small at Tt1
. The isothermal total entropy change (ΔST
) is large and positive, due to the different electronic density of states of both phases. Tohei et al.  deduced ΔST
from magnetization, and Burriel et al.  determined directly the adiabatic temperature increment ΔTS
. Nevertheless the actual ΔST
can differ substantially from the indirect determinations. The transition temperature Tt1
decreases with the applied field and is very sensitive to the deficit of C, disappearing already for x
= 0.05. For our sample (x
=0.02) the unit cell a
= 3.8951(1) Å and Tt1
are higher than those reported on references [1,2,3] indicating a higher C content. The heat capacity at zero field shows a single transition from AF phase directly to F phase without an intermediate canted ferromagnetic phase (CF), but this phase does appear for fields above 1 T. The transition temperature from CF to F, Tt2
= 167 K is only weakly decreasing with the field and with x
which makes possible the appareance of the CF phase at zero field for samples with higher x
and, consequently, Tt1
. The application of a field to the present sample between 169 K and 171 K transforms the AF phase to the F one, but for T < 167 K the transformation is to the CF phase.The direct determination of ΔST
varying from 0 to 6 T indicates a strong and inverse MCE with ΔST
= 13.11±0.15 J/kg.K, nearly constant between 148 and 169 K and a normal MCE out of this range. Field variations up to less than 6 T produce a higher positive ΔST
value but in a narrower temperature interval. This effect is the result of the positive entropy jump at the transition and the negative normal entropy variation before and after it, for the AF and CF or F phases. The results agree in value with those deduced from heat capacity but disagree in the temperature range, due to the hysteresis. On the contrary, results from magnetization [1,3] gave values too high, may be due to the failure of the Maxwell relation. The Clausius-Clapeyron equation gives an entropy jump at the transition of 14.2 J/kg.K, which agrees with the results from heat capacity and the limit for small field variation in direct determinations.
 T.Tohei, H. Wada, and T. Kanomata, J. Appl. Phys. 94, 1800 (2003).  R. Burriel, L. Tocado, E. Palacios, T. Tohei, and H. Wada, J. Magn. Magnet. Mat. 290-1, 715 (2005). B.S. Wang, P.Tong, YP. Sun, W.Tang, LJ. Li, X.B.Zhu, Z.R.Yang, W.H.Song, Physica B 405, 2427 (2010).
9:00 PM - FF3.16
Spin Reorientation Transition: Phase Diagrams and Entropy Change.
Vittorio Basso 1 , Carlo Sasso 1 , Michaela Kuepferling 1 Show Abstract
1 , INRIM, Torino Italy
In a spin reorientation process the spontaneous magnetization changes orientation when the temperature is changed. The origin of the process is the presence of competing anisotropies, for example the joint presence of an easy axis and an easy plane [1–3]. The subject has been investigated in detail in the past [4, 5], however a renewed interest on the topic has been challenged by the consideration of the presence of a latent heat associated with the spin reorientation transition  and therefore for the associated magneto-caloric effect. Magnets with a spin reorientation may represent an interesting new class of materials for magnetic refrigeration alternative to the materials with a magneto-structural transformation. Even if the intensity of the entropy change is not high , the entropy change is simply achieved by changing the orientations of the moments. Therefore, in contrast to the usual process in which one has to apply and remove large magnetic fields, one may consider rotate the magnetic field in order to reorient the spins. In this paper we investigate this process theoretically by taking uniaxial anisotropy energy up to the third order. The corresponding entropy change is calculated. The study is applied in particular to the CoZn W-type ferrite of composition BaCo0.62Zn1.38Fe16O27  and to Er2Fe14B1 . The theory predicts that the full entropy change can be achieved in a large temperature range proportional to the magnetic field, as wide as about 50 K applying 1 T for ErFeB.The research leading to these results has received funding from the European Community’s 7th Framework Programme under grant agreement No. 214864. E.P. Naiden and S.M.Zhilyakov, Phys. Solid State 39, pp. 967-968 (1997)  G.Asti, F.Bolzoni, F.Licci,and M.Canali, IEEE Trans. Magn. 14, pp. 883-885 (1978)  M. I. Ilyn and A. V. Andreev, J.Phys.: Condens. Matter 20, 285206(4pp) (2008)  G. Asti, ”First-order magnetic processes” in Ferromagnetic Materials Vol.5 (K.H.J. Buschow and E.P. Wohlfarth eds.) pp 397-464, Elsevier, Amsterdam (1990). M. H. Yu, Z. D. Zhang, F. R. de Boer, E. Bruck and K. H. J. Buschow , Phys. Rev. B 65, 104414 (2002)  A.T. Pedziwiatr, B.F. Bogacz, A. Wojciechowska, S.Wrobel, Journal of Alloys and Compounds 396, pp.54-58 (2005)  M.Kuzmin and M. Richter, Appl. Phys. Lett. 90, 132509 (2007) K.P. Skokov, Yu.S. Koshkod'ko, Yu.G. Pastushenkov, J. Lyubina, O. Gutfleisch, Proceedings of the third IIF-IIR Int. Conf. on Magnetic Refrigeration at room temperature (P.Egolf, editor), Refrigeration science and technology proceedings n. 2009-3, International Institute of Refrigeration, Paris, 2009.
9:00 PM - FF3.17
Latent Heat in First Order Magnetocaloric Materials.
Kelly Morrison 1 , A. Caplin 1 , K. Sandeman 1 , L. Cohen 1 Show Abstract
1 Physics, Imperial College, London United Kingdom
The magnetocaloric effect has the potential to be used for room temperature refrigeration applications, and as a result has been of increased research interest over the last 10 years. It is argued that materials which exhibit a first order phase transition may be preferable due to their associated large temperature changes. The disadvantages of most first order systems are their associated thermal and magnetic hysteresis. We have shown recently how to separate the latent heat and heat capacity contributions to entropy change in magnetocaloric systems., In our calorimetric probes the sample size is limited to dimensions of the order of 100μm. For well defined calorimetric behaviour a correlation length (of the order parameter) on the same lengthscale is typically advantageous. In a parallel activity, the use of Hall probe imaging on the bulk sample can be used to confirm the nucleation and growth mechanism indicative of the first order phase transition and to identify the correlation length, which we define as the size of the nucleating region. Here we show the manifestation of latent heat measured by our adiabatic temperature probe as the correlation length decreases. Examples will be given of systems where the first order phase transition is dominated by either nucleation or growth. It will be shown that measurements so far suggest a correlation length, ξ, of the order of 20-100μm in local moment systems, even when heavily disorder broadened. Stark differences in the nucleation and growth process on sweeping the magnetic field up and down can arise, as was previously reported from Hall probe imaging of Gd5Ge2Si2, which we show also manifests in the latent heat measurements. For itinerant magnetic systems such as La(Fe0.88Si0.12)13 data suggests that ξ varies significantly with temperature, decreasing as the temperature is increased above Tc resulting in a latent heat that is observed to be broad with respect to field. There are also significant variations in the relative contribution of changes in heat capacity to the entropy change, which can have important implications to the adiabatic temperature change, ΔTad.  - Y.Miyoshi et al., Rev. Sci. Instrum. 79 074901 (2008) - K. Morrison et al., J. Phys. D: Appl. Phys. 43 132001 (2010) - G.K. Perkins et al., J. Phys. Condens. Mat., 19 176213 (2007) - Y.Imry et al., Phys. Rev. B 19 3580 (1979) - J.D. Moore et al., Adv. Mater. 21 1-4 (2009)
9:00 PM - FF3.18
Magnetic and Magnetocaloric Properties of Gd2C.
Yaroslav Mudryk 1 , Vitalij Pecharsky 1 2 , Karl Gschneidner, Jr. 1 2 Show Abstract
1 Division of Materials Science and Engineering, The Ames Laboratory of the US Department of Energy, Ames, Iowa, United States, 2 Department of Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
The Gd2C has the Curie temperature of ~75 °C, and contains 96.3 wt.% of Gd thus warranting an investigation of its magnetocaloric properties despite its tendency to hydrolyze in humid air. Here we report on the magnetic properties of both as cast and heat treated samples, prepared by using the conventional arc melting technique. The magnetic transition is broad, and the maximum magnetic entropy change calculated using the Maxwell equation is small, -3.8 J/Kg K for 0 to 50 kOe magnetic field change at ~70 °C.
9:00 PM - FF3.19
Multy Cirquit Magnetic Refrigerator Device.
Sergey Taskaev 1 , Vasiliy Buchelnikov 1 Show Abstract
1 Physics, Chelyabinsk State University, Chelyabinsk Russian Federation
Magnetic refrigeration near room temperature is one of the promising energy saving technologies up to date. In this work we present the recent results of constructing the multy circuit magnetic refrigeration device. This device is an improvement of the previous single circuit setup and it has some good features. Magnetic system of this device is axial composite Nd-Fe-B permanent magnetic system with residual magnetic induction equal to 1.9T inside 18 mm air gap. Magnetic material is prepared as sets of pure Gd plates. As a heat fluid we use pure water with addition of corrosion inhibitor. This work was financially supported by RF President grant for young scientists MK-1891.2010.2.
9:00 PM - FF3.2
Influence of Different High Temperature and Short Time Annealing on Phase and Magnetic Properties in the LaFe13-xSix (x=1.3,1.4,1.5,1.6) Compounds.
Chen Xiang 1 , Chen Yungui 1 , Tang Yongbai 1 Show Abstract
1 , Sichuan University, Chengdu China
The LaFe13-xSix (x=1.3,1.4,1.5,1.6) compounds were prepared by arc-melting and annealed at high temperature of 1523K(5h), 1373K(2h)+1523K(5h), and 1523K(5h)+1373K(2h), respectively. The phase relation, microstructure, magnetic properties were investigated. The analyses of powder X-ray diffraction and scanning electron microscopy (SEM) showed that the main phase is NaZn13-type phase in those compounds annealled at above mentioned methods. The impurity phases in LaFe13-xSix (x=1.3,1.4,1.5,1.6) are different. For LaFe11.7Si1.3, the impurity is a certain amount of -Fe and small La5Si3 phase. Although there is no La5Si3 phase, a few LaFeSi phase and a certain amount of -Fe were found in LaFe13-xSix (x=1.4,1.5,1.6) compounds. From the analysis of X-ray and SEM , the heat treatment proces of 1523K(5h)+1373K(2h) was more optimal than the other methods, and the amount of impurity phases was lowest in samples annealled at 1523K(5h)+1373K(2h). Magnetic measurements were performed for LaFe13-xSix(x=1.3,1.4,1.5,1.6) compounds annealled at 1523K(5h)+1373K(2h) by using a vibrating-sample magnetometer. With the increasing of Si, the Curie temperature shifted to high temperature and were 185, 190,194, and 199 K, respectively. The thermal hysteresis, magnetic hysteresis, and Arrott plots around magnetic transition temperatures showed a typical the first order of magnetic behavior in those compounds. Under a low applied magnetic field of 2 T, large magnetic entropy changes around the magnetic transition temperature were 23.8,25.3,17.6, and 14 J/kg K, for x =1.3, 1.4, 1.5, and 1.6, respectively. The magnetic properties of LaFe13-xSix compounds annealed by high temperature and short time was equivalent to that of compunds annealled by the traditional method. It indicated that high temperature and short time annealing was an potentful mentod for preparing for LaFe13-xSix (x=1.3,1.4,1.5,1.6) compounds.
9:00 PM - FF3.21
Giant Electrocaloric Effect in High-energy Electron Irradiated P(VDF-TrFE) Copolymers.
Sheng-Guo Lu 1 , Xinyu Li 1 2 , Jiping Cheng 1 , Lee Gorny 1 , Qiming Zhang 1 2 Show Abstract
1 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
A direct calorimetry method was developed and used to measure the electrocaloric effect (ECE). A temperature change deltaT over 20 dgreeC and an entropy change deltaS over 95 J/(kgK) were procured at 306 K and 160 MV/m in the high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) 68/32 mol% copolymers, which were larger than those of terpolymer blends (ΔT = 9 °C, ΔS=45.6 J/(kgK) at 180 MV/m and room temperature) and our earlier report on P(VDF-TrFE) 55/45 mol% normal ferroelectric copolymer (12 °C and 55 J/(kgK) at 70 °C). We observed that the β value (9.9 JmC^-2K^-1) in the equation of ΔS=1/2βΔD2 derived from ΔS - ΔD^2 relation for irradiated copolymers was larger than that of the terpolymer blends (5.3 JmC^-2K^-1). It was also found that the irradiated copolymer showed a sharp depolarization peak at Td < Tm (maximum permittivity temperature), which is frequency independent, in the dielectric constant - temperature characteristics, a larger depolarization value at Td in the thermal stimulated depolarization current (TSDC) - temperature relationship, and a larger volume strain/longitudinal strain ratio over terpolymer blends. The giant ECE in irradiated copolymer is regarded as due to the more randomness in relaxor state, ease of reorientation of domains and a larger polarization generated when a high electric field is applied. In irradiated copolymers, the long all-trans chains are broken by the high-energy electrons, which make the small sized all-trans sequences more easily reorient along the electric field, more remarkably affecting the permittivity, TSDC, and volume strain. In terpolymer blends, however, the chemical doping derived crosslinks of backbone chains make the nanometer-sized all-trans sequences harder to reorient along the electric field, thus contributing less polarization and volume strain, as well as smaller ECE.
9:00 PM - FF3.3
Effect of Co and C on the Corrosion Behavior of LaFe11.5Si1.5 Materials in Distilled Water.
Min Zhang 1 , Yi Long 1 , Rong-chang Ye 1 Show Abstract
1 , University of Science and Technology Beijing, School of Material Science and Engineering, Beijing China
Although the LaFeSi materials with NaZn13-type structure,which are suggested to be promising magnetocaloric materials, have been extensively studied in the past years, few researches have been focused on their corrosion behavior. For practical application, the corrosion is inevitable in corrosion environment. Elements and structure are the most crucial factors in development of corrosion. In this paper, corrosion behaviors of three different alloys, base alloy LaFe11.5Si1.5, Co containing alloy (LaFe10.87Co0.63Si1.5) and LaFe10.87Co0.63Si1.5C0.2 alloy, were studied. XRD, weight loss, SEM, potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) techniques were applied to study the corrosion behavior in distilled water. The X-ray diffraction patterns of the samples indicated that the matrix phases of all alloys were 1:13 phase after annealing 15 days at 1423K. Additionally, a small amount of α-Fe phase and La-rich phase coexisted in the samples according to SEM back-scattered electron image. Weight loss measurements in distilled water indicated that the corrosion rate order was LaFe11.5Si1.5>LaFe10.87Co0.63Si1.5>LaFe10.87Co0.63Si1.5C0.2. Potentiodynamic polarization curves exhibited that the replacing Fe with Co affected mainly the anodic dissolution process, the anodic current density was lower for LaFe10.87Co0.63Si1.5 than that for LaFe11.5Si1.5. However, the addition of C affected both the anodic and cathodic process. Both the anodic current density and cathodic current density for LaFe10.87Co0.63Si1.5C0.2 were the lowest among the three different alloys. The corrosion current density was 2.655 μAcm-2, 1.833 μAcm-2 and 1.329 μAcm-2 for LaFe11.5Si1.5, LaFe10.87Co0.63Si1.5 and LaFe10.87Co0.63Si1.5C0.2, respectively. Polarisation resistance obtained from Nyquist plots was highest for LaFe10.87Co0.63Si1.5C0.2 alloy and lowest for LaFe11.5Si1.5 alloy among the three different alloys. Furthermore, SEM micrographs showed that pitting corrosion occurred in the matrix phase in all the three different alloys. Corroded spots in LaFe10.87Co0.63Si1.5C0.2 alloys decreased obviously under the same experiment condition. XPS results provided additional basis for the interpretation of the corrosion mechanism for the three different alloys. Above results indicated that the order of corrosion resistant is LaFe10.87Co0.63Si1.5C0.2 > LaFe10.87Co0.63Si1.5 > LaFe11.5Si1.5. So the replacing of Fe with Co and addition of C increases the anti-corrosion ability for the alloys.
9:00 PM - FF3.4
Magnetocaloric Effect in Rare Earth-based Metallic Glasses.
Norbert Mattern 1 , Bjorn Schwarz 1 , Juergen Eckert 1 Show Abstract
1 , Leibniz_Institute IFW Dresden, Dresden Germany
Rare Earth-based metallic glasses exhibit a magnetic transition between 10 K and 150 K depending on the kind of RE-element. The magnetic properties can be also changed by the content of the RE-element as well as by addition of further transition metals. Magnetocaloric effect and refrigerant capacity of Gd-based Gd60FexCo30−xAl10 metallic glassesare investigated for x = 0, 10 , 20 and 30. It is found that the non-linearity of saturationmagnetization in crystalline Co-Fe binary alloys can be transferred to the quaternary metallicglass. Whereas the magnetocaloric specific values of Gd60Co30Al10 are comparable in magnitude with those of other Gd-based metallic glasses, Fe addition leads to an increase of the saturation magnetization and refrigerator capacity with a maximum for x = 20. Simultaneously, the temperature of maximum isothermal change of magnetic entropy increases from 145 K to 200 K with increasing Fe-content and also the halfwidth S-T-curve isconsiderably broadened. Furthermore, the effect of thermal treatment will be reported.
9:00 PM - FF3.5
Correlating Magneto-caloric Properties in Co-doped Bulk La-Fe-Si from the First- to Second-order Type Behaviour.
James Moore 1 , K. Skokov 1 , J. Liu 1 , M. Krautz 1 , A. Barcza 2 , M. Katter 2 , O. Gutfleisch 1 Show Abstract
1 Institute for Metallic Materials, IFW Dresden, Dresden Germany, 2 , Vacuumschmelze GmbH & Co. KG, Hanau Germany
The ternary alloy system LaFe13-xSix shows a giant magnetocaloric effect associated with the thermally- or field-induced transition from paramagnetic to ferromagnetic state, which occurs simultaneously with coupled magneto-structural transformation. Addition of Co both increases the Curie temperature from 200 K to 340 K and causes a gradual change from first-order type to second-order type behaviour. The most reliable method for determining magneto-caloric properties is direct measurement of adiabatic temperature change ΔTAD. This can supply important information on the dynamics of thermo-magnetic processes and on magnetic hysteresis during the field-induced magnetic transition. At the same time in first-order type transitions, various anomalies in the temperature dependences of lattice parameters are possible, which lead to an additional lattice contribution to the magneto-caloric effect.In the present work the La(Fe,Co,Si)13 alloys were prepared by reactive sintering method as described by Katter et al. . We show ΔSM calculated from Maxwell relation, ΔTad by the direct measurement method, and ΔVad associated with isotropic volume expansion, and report on correlations between these parameters as the transition evolves.The research leading to these results has received funding from the European Community’s 7th Framework Programme under grant agreement No. 214864. Katter M., Zellmann V., Reppel G.W., Uestuener K., 2008 Magnetocaloric properties of La(FeCoSi)13 bulk material prepared by Powder Metallurgy, IEEE Trans. Magn. 44, 3044-47.
9:00 PM - FF3.6
Magnetic Field Induced Corrosion Patterning of Ferromagnetic Electrodes.
Annett Gebert 1 , Ralph Sueptitz 1 , Jakub Adam Koza 1 , Margitta Uhlemann 1 , Ludwig Schultz 1 , Kerstin Eckert 2 , Xuegeng Yang 2 Show Abstract
1 , IFW Dresden, Dresden Germany, 2 Institute for Fluid Dynamics, Technical University Dresden, Dresden Germany
The magnetization of a ferromagnetic electrode in an external homogeneous magnetic field leads to a stray field in front of the electrode surface. This stray field and its gradients can significantly alter the free corrosion and anodic polarisation behaviour. To investigate the influence of an superimposed magnetic field on the surface profile evolution of a corroding cylindrical Fe electrode, potentiostatic polarisation measurements were performed in a 0.5 M H2SO4 solution (pH 0.25) without and with applied fields up to 0.6 T. Also long time exposure experiments were performed in 0.001 M HCl under free corrosion conditions with and without field influence. Afterwards the surface of the electrode was investigated by means of optical microscopy and profilometry. At low anodic overpotentials and in the passive state no influence of the superimposed magnetic field on the electrode surface profile was observed. But a localization of the corrosion reaction to the centre of the cross-sectional area of the Fe cylinder was observed when the dissolution was diffusion-limited. During long time exposure the electrode corroded uniformly. Under the influence of a magnetic field the corrosion reactions occurred localized, i.e. at the centre of the electrode while the rim was not affected. The observed effects of a superimposed magnetic field are discussed with respect to an increase of the mass transport due to the Lorentz force driven magneto-hydrodynamic (MHD) effect and the magnetic field gradient force and its interaction with the paramagnetic Fe ions.
9:00 PM - FF3.7
Modeling of the Magnetocaloric Effect in Heusler Ni-Mn-X (X = In, Sn, Sb) Alloys Using Antiferromagnetic Five-state Potts model with Competing Interactions.
Vladimir Sokolovskiy 1 , Vasiliy Buchelnikov 1 , Konstantin Kostromitin 1 Show Abstract
1 Condensed Matter, Chelyabinsk State University, Chelyabinsk Russian Federation
In recent years, theoretical and experimental investigations of the magnetocaloric effect (MCE) in magnetoordered materials are very important, because materials with large MCE values can be use as refrigerants in a magnetic cooling technology. Recent researches have shown that ferromagnetic (FM) Heusler alloys such as Ni-Mn-X (X = In, Sn, Sb) are also the perspective materials by way of refrigerants in cooling devices. In these compounds the two types of large MCE (positive (ΔT> 0) and negative ΔT < 0) in the vicinity of the room - temperature are observed experimentally .The gigantic MCE observed in these compounds as well as in Gd-Ge-Si, Mn-As, La-Fe-Si compounds. The reason of negative MCE is following: recent experimental studies of non-stoichiometric Ni2Mn1+xX1-x alloys have shown antiferromagnetic (AFM) interactions between Mn atoms in the low-temperature tetragonal phase, while in the high-temperature cubic phase the AFM interactions are suppressed by FM interactions. In this work we present theoretical model for description of reasons of positive and negative MCE in Ni-Mn-X (X = In, Sn, Sb) alloys by Monte Carlo simulations. We consider the five – state AFM Potts model with competing FM and AFM interactions on three dimensional hypercubic lattice with periodic boundary conditions. The model Hamiltonian describes the discrete Potts spins on a bipartite lattice with AFM interactions between spins on different sublattices and FM interactions within the same sublattice. The magnetic part of entropy calculates by the help of mean – field approximation using information about density of Potts spin states. The paramagnetic (PM), FM, AFM phases and phase with a broken sublattice symmetry (BSS) can occur in the system depending on relation the FM to AFM interactions . The BSS phase is a phase in which one spin state is favored on one sublattice and on the other sublattice the q - 1 states are distributed with equal probability.Our simulations show that for the case of the strong AFM interaction the FM→BSS→PM phase transitions can occur in the system. The negative MCE observes at FM→BSS transition, while the positive MCE occurs at BSS→PM transitions. For the case of strong FM interaction the FM→PM phase transition occurs with the positive MCE. The same sequences of MCE in Heusler Ni-Mn-X (X = In, Sn, Sb) alloys are experimentally observed . We assume that the presence of BSS phase at the low temperature region can explain an occurrence of the negative MCE in Heusler Ni-Mn-X (X = In, Sn, Sb) alloys.1. A. Planes et al., J. Phys.: Condens. Matter 21, 233201 (2009).2. J. R. Banavar, F.Y. Wu, Phys. Rev. B, 29, 1511 (1984).
9:00 PM - FF3.8
Phase Diagrams of Ni2+xMn1-xGa Heusler Alloys from Hubbard Hamiltonian with Account of Jahn Teller Effect.
Mikhail Zagrebin 1 , Vasiliy Buchelnikov 1 Show Abstract
1 , Chelyabinsk State University, Chelyabinsk Russian Federation
Heusler Ni-Mn-Ga alloys are interesting for practical applications because of the numerous unusual effects such as a shape memory effect in ferromagnetic state, a giant magnetocaloric effect. Existence of magnetic and structural phase transitions leads to occurrence of these effects . Experimental studies and ab initio calculations of band structure of Ni-Mn-Ga alloy show, that Jahn Teller effect plays important role in phase transitions in Heusler alloys [1-3]. Jahn Teller effect is in the present case associated with eg states as shown in calculations of DOS for Ni-Mn-Ga alloys . In this work microscopic Hubbard model Hamiltonian for isotropic twice degenerate ferromagnet with account of Jahn Teller effect is investigated. Macroscopic free energy is obtained from the microscopic Hubbard Hamiltonian [4,5]F=a2e2/2+a3e3/3+a4e4/4+b2m2/2+b4m4/4+Ce2m2/2 (1)where e – tetragonal distortion, m – magnetization, ai – elastic modulus, bi – exchange constants and C – magnetoelastic constant. All coefficients depend on microscopic parameters: temperature T and composition x. As a result of analytical minimization of free energy (1) with respect to m and e the phase diagrams are numerically constructed. It is shown that at certain values of parameters on the phase diagrams the thermodynamic paths exist which can explain experimentally observed sequences of phase transitions . Using density of states for different compositions x [6,7] the T-x phase diagram is numerically constructed. This phase diagram can explain experimentally observed behavior of temperatures of phase transitions on composition x. Work was supported by grant Dynasty foundation and RFBR grant 10-02-96020_ural.1. P. Entel et al. J. of Physics D: Appl. Physics, 39, 865 (2006).2. S. Fujii et al. J. Phys. Society of Japan, 58, 3657 (1989).3. P. Entel et al. Materials Science Forum, 635, 3 (2010).4. D.K. Ray et al., Phys. Rev. B, 33, 5021 (1986).5. A. Popkov et al., JETP, 104, 943 (2007).6. A. Chakrabarti et al., Phys. Rev. B, 72, 073103 (2005).7. S. Banik et al., Phys. Rev. B, 75, 104107 (2007) .
9:00 PM - FF3.9
Topological Modeling of Martensitic Transformation in a Ni2MnGa Alloy.
Xiao Ma 1 , Zhaozhao Wei 1 Show Abstract
1 Metallic Materials Science and Engineering, South China University of Technology, Guangzhou, Guangdong, China
A number of models have been put forward in the past decades to explain the experimental observed crystallographic features of martensite transformation. The major theory is phenomenological theory of martensite crystallography which does not really describe the actual mechanism of the transformation process. The foundation of the theory is purely mathematics manipulation which relates the parent and martensite phase . To overcome the limitation of the previous theory, Pond and co-workers developed a brand new theory describing the martensite transformation, which was based on the step-style structure of inter-phase interface and the boundary dislocation theory, namely Topology Model. The up-to-date treatment is to analyze the habit plane structure directly based on recent studies of inter-phase interface by the tool of TEM and HRTEM. It describes the actual mechanism of atomic transformation in some level. Also, the mathematics foundation of this theory is based on a second approximation method providing a degree of simplicity not found before. Theory of Topological modeling has been already applied to the Ti alloy and the Ferrous alloy successfully . The Ferrous Shape Memorize Alloy has a promising prospect of application in future for its advantages of both large output strain and short reaction time. However, the research of the alloy is mostly about thermodynamics and the fabrication, while the crystallographic part is barely mentioned. Our present work is to analyze the crystallographic features of Ni53Mn25Ga22 alloy using the Topology Model. In the analysis, the inter-phase interface consists of coherent terraces segments reticulated by arrays of localized defects which are to accommodate the coherent strain without causing long-range strain. One of the arrays of defects is namely disconnection with burgers vector b=0.058nm while the other is namely lattice invariant dislocation chosen as twinning system with twinning plane (112)α and twinning direction 0.186[1-11]α. Under the condition that K-S orientation relationship is met, the terrace plane is selected as (111)γ // (101)α. The major crystallographic features of the Ni53Mn25Ga22  alloy are predicted. The habit plane is determined to be (-0.859, 0.048, -0.51)γ or (-0.895, -0.061, -0.441)α presented in γ phase and α phase frame respectively, of which the inclination with terrace plane is ψγ=2.694° and ψα=2.789°.
Oliver Gutfleisch IFW Dresden
Karl G. Sandeman Imperial College London
Aru Yan Chinese Academy of Sciences
Asaya Fujita Tohoku University
Karl Gschneidner Iowa State University
FF4: Magneto Calorics and Magnetic Cooling IV
Tuesday AM, November 30, 2010
Republic A (Sheraton)
9:30 AM - **FF4.1
Caloric Effects in Heusler Shape-memory Alloys.
Antoni Planes 1 , Lluis Manosa 1 , Acet Mehmet 2 Show Abstract
1 Estructura i Constituents de la Matèria, Universitat de Barcelona, Barcelona Spain, 2 Experimentalphysik, Universität Duisburg-Essen, Duisburg Germany
Magnetic Heusler alloys which undergo a first-order martensitic transition display important functional properties including magnetic shape-memory and superelasticity effects. Thanks to a strong coupling between the structure and magnetism, in these systems the martensitic transition can be induced by application of both magnetic and mechanical (stress) fields. Consequently, the resulting changes of entropy related to the transition provide these materials with caloric effects associated with tuning both fields. In this talk, after a brief discussion of the thermodynamics of systems with magnetostructural coupling, we will survey the (magneto- and other) caloric properties of Ni-Mn-Z (Z= Ga, In, Sn, …) Heusler materials. In particular, we will show that in the Ni-Mn-In alloy family the high and low temperature phases show significant differences of magnetic moment and unit cell volume that lead to interesting magnetocaloric and barocaloric effects. In these alloys application of a moderate hydrostatic pressure (few kbar) gives rise to a (conventional) barocaloric effect with a magnitude comparable to the (inverse) magnetocaloric effect.
10:00 AM - FF4.2
Features of the Adiabatic Temperature Change in Ferromagnetic Shape Memory Alloys in the Vicinity of Direct and Reverse Martensitic Transformation.
Vladimir Khovaylo 1 , Konstantin Skokov 2 3 , Alexei Karpenkov 3 , Oliver Gutfleisch 2 Show Abstract
1 , National University of Science and Technology "MISiS", Moscow Russian Federation, 2 Leibniz Institute for Solid State and Materials Research Dresden, Institute for Metallic Materials, Dresden Germany, 3 Faculty of Physics, Tver State University, Tver Russian Federation
Recently, a considerable interest has been paid to magnetocaloric effect in materials undergoing first-order magnetostructural phase transitions. Particularly, a large isothermal magnetic entropy change comparable to that observed in Gd5(Si1-xGex), La(Fe1-xSix)13, etc., has been reported for Heusler-based ferromagnetic shape memory alloys Ni-Mn-X (X = Ga, In, Sn, Sb) which undergo a first-order magnetostructural phase transition. Here we present results of direct measurements of the adiabatic temperature change ΔTad and discuss its features in representatives of these materials, Ni-Mn-Ga and Ni-Mn-Sn, which exhibit ordinary and inverse magnetocaloric effect, respectively. Common feature of the adiabatic temperature change in Ni-Mn-Ga and Ni-Mn-Sn measured under repeatable action of magnetic field is that ΔTad is irreversible in the vicinity of magnetostructural transition temperature. The irreversibility is greatly diminished after the first cycle of application and removal of the magnetic field, which is accompanied by a sizeable reduction in the magnitude of the adiabatic temperature change, and ΔTad adopts practically reversible character upon subsequent cycles of application and removal of the magnetic field. The major difference between these alloys is that the adiabatic temperature change in Ni-Mn-Ga demonstrates an irreversible character in the vicinity of the direct martensitic transformation from high-temperature austenitic to low-temperature martensitic state whereas in Ni-Mn-Sn irreversibility of ΔTad is observed upon the reverse transformation from low-temperature martensitic to high-temperature austenitic state. It is shown that all these features of the adiabatic temperature change in ferromagnetic shape memory alloys can readily be understood considering thermodynamics of temperature- and magnetic-field-induced martensitic transformations. Essential factors governing adiabatic temperature change ΔTad in ferromagnetic shape memory alloys are outlined.
10:15 AM - FF4.3
Jun Cui 1 2 , John Lemmon 1 , Larry Jones 4 , Thomas Shield 3 , Manfred Wuttig 2 Show Abstract
1 Energy and Environment Directorate, Pacific Northwest National Lab, Richland, Washington, United States, 2 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 4 Materials Preparation Center, AMES Laboratory, Ames, Iowa, United States, 3 Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota, United States
The magnetocaloric effect is a thermodynamic phenomenon that causes certain materials to heat up when magnetized and to cool down when demagnetized. Refrigeration based on the magnetocaloric effect is possible but requires large magnetic fields and large amount of working material, which typically contain rare earth elements. Experiments were conducted to simulate this process using a first order phase transformation induced by stress in a particular Ni3MnGa1.4 alloy. Specimens were stress-biased into their Martensitic phase at 313 K (stress free martensite start transformation temperature is 309 K) and this was found to cause the magnetization of the sample to increase from 15 emu/g to 24 emu/g under the applied field of 7 kOe. This indicates a coupling of the first order cubic to tetragonal phase transformation and the second order magnetic transition. This result is significant because a large change in the magnetic entropy that previously required a large applied field with other materials can be achieved by a combination of stress and a smaller magnetic field applied to this alloy. In addition, applied stress changes the magnetic transition temperature (by 0.23 K/MPa) at which the material exhibits maximum cooling effect, which extends the useful temperature range of the alloy.
11:00 AM - **FF4.4
Optimization of La(Fe,Si)13- and NiMn- based Materials for Magnetic Refrigeration.
Feng-xia Hu 1 , Jun Shen 2 1 , Jin-liang Zhao 1 , Ji-rong Sun 1 , Bao-gen Shen 1 Show Abstract
1 State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing China, 2 Key Laboratory of Cryogenics, Technical Institute of Physics and Chemistry,Chinese Academy of Sciences, Beijing China
An increasing attention has been attracted to magnetocaloric cooling technology due to the recent discoveries of magnetocaloric materials that exhibit large magnetocaloric effect (MCE) . The La(Fe,Si)13- and NiMn- based compounds have attacted much attention since the first discovery of great MCE in these materials [2,3]. LaFe13-xSix compounds with NaZn13 structure stabilized in the concentration region 1.2 ≤ x ≤ 2.6. Great MCE takes place in LaFe13-xSix with lower Si concentration 1.2 ≤ x ≤ 1.6 due to the first-order nature of the magnetic phase transition at Curie temperature TC and the field-induced itinerant electron metamagentic (IEM) transition above TC. However, the TC of these LaFe13-xSix is around 200K, far away from room temperature, and large hysteresis loss exists because of the first-order nature of the transition. Therefore, increasing TC and simutanously reducing hysteresis loss is the first key step to realize the application of these materials in a room temperature refrigerator. Previous investigations indicated that the IEM transition and the corresponding hysteresis behavior are closely related to the spin fluctuation. To systematically adjust local environments of Fe atoms and thus influence exchange interaction and spin fluctuation, we introduced magnetic rare-earth atoms (e.g. Pr, Nd, Ce), and/or transition atoms (e.g. Co), and/or interstitial atoms (e.g. C and/or H), and/or non- magnetic atoms (e.g. Cu, Ge) in the structure of La(Fe,Si)13. As TC is pushed to higher temperature, it was found that the magnitude of magnetic entropy change (ΔS) reduces more or less depending on the adopted method. The reduction of |ΔS| is the smallest when only interstitial H atoms are introduced. However, the La(Fe,Si)13 interstitial H compounds do not show good thermal stability. The compounds begin to lose H if the temperature exceeds 423K. Our recent experiments reveals that the simultaneous introduction of interstitial C and H atoms in a Pr-doped LaFeSi can remarkably enhance the thermal stability and, importantly, lead to a great |ΔS| near room temperature without hysteresis loss. A temperature as high as 573K can not make H atoms escape from the compounds. We also optimized MCE of NiMn-based Heusler alloys. Large ΔS with small thermal hysteresis was observed in metamagnetic alloys Ni51Mn49-xInx. With tuning In content, martensitic temperature TM can be shifted in a wide temperature range around room temperature while the thermal hysteresis keeps small, < 2 K and the ΔS peak shows a table-like peak under a magnetic field of 5T. This work was supported by the National Natural Science Foundation of China, the Knowledge Innovation Project of the Chinese Academy of Sciences and the National Basic Research of China.*Corresponding email: firstname.lastname@example.org K. A. Gschneidner Jr., et al, Rep. Prog. Phys. 68, 1479 (2005). F. X. Hu, et al, Appl. Phys. Lett. 76, 3460 (2000). B. G. Shen, et al, Adv. Mater. 21, 4545 (2009).
11:30 AM - FF4.5
Small Hysteresis Behavior in La(Fe0.86Si0.14)13H1.1 after Sharpening of the Itinerant Electron Metamagnetic Transition by External Pressure.
Asaya Fujita 1 , Shun Fujieda 2 , Kazuaki Fukamichi 2 Show Abstract
1 Depatment of Materials Science, Tohoku University, Sendai Japan, 2 Institute of Multidisciplinary Research for Advanced Materials Research, Tohoku University, Sendai Japan
In La(FexSi1−x)13 and their hydride, large magnetocaloric effects (MCEs): the magnetic entropy change ΔSm and the adiabatic temperature change ΔTad are induced by the itinerant-electron metamagnetic (IEM) transition above the Curie temperature TC. However, the IEM transition causes the loss of efficiency in magnetic refrigeration because of a hysteresis behavior of the first-order phase transition. Therefore, the reduction of hysteresis loss with retaining large values of MCEs is one of the important issues. The partial substitution of Ce or Pr for La in the compound with x = 0.86 makes ΔSm large as the same magnitude of that with x = 0.88, while a small hysteresis associated with the lower Fe concentration is maintained. The enhancement of ΔSm by the partial substation is partly attributed to the sharpness of the IEM transition derived from the reduction of volume associated with the smaller atomic radius of Ce or Pr. Indeed, the pressure-induced enhancement of ΔSm is clearly confirmed in La(Fe0.86Si0.14)13H1.1. On the other hand, a small hysteresis after partial substitution evokes that the sharpening of the IEM transition by volume change is separately caused with the change of hysteresis. In the present study, the hysteresis of the IEM transition for La(Fe0.86Si0.14)13H1.1 is evaluated by applying hydrostatic pressure to discuss the origin of the small hysteresis after sharpening of the IEM transition by volume reduction.In the range 0.00≤ p ≤ 0.25 GPa, no clear hysteresis of the IEM transition is observed, while the maximum of the magnetic entropy change ΔSmmax is increased from -9 to -12 J/kg K under a magnetic field change of 2T. By increasing p from 0.50 to 1.00 GPa, the hysteresis loss Eh at TC evaluated from the area of hysteresis regions of magnetization curve increases from 0.3 to 14.1 J/kg. The value of ΔSmmax at 1.00 GPa is about -18 J/kgK, therefore, the increase of Eh at TC is more significant than that of ΔSmmax. One of the reasons for the increase of Eh at TC is the reduction of thermal energy due to the decrease of TC by applying pressure. According to the Landau expansion theory, the temperature dependence of the energy barrier Eb between the ferromagnetic and paramagnetic state is governed by the third power of the 4th order Landau coefficient B(T)3 of the magnetic free energy. Since Eh at TC is directly connected with Eb, the contribution of thermal energy to Eh is evaluated by taking the relation B(T)3∝T3 into account. Actually, the changing rate of Eh is close to the third power of the decrease of TC by pressure, showing that the change of Eh by applying pressure is mainly attributed to the reduction of thermal energy. In other words, no significant influence of Eh by pressure, such as a change of energy barrier as a function of volume reduction, is observable. Consequently, the volume reduction makes the IEM transition sharper with retaining small energy barrier, resulting in a large ΔSm with a small Eh.
11:45 AM - FF4.6
Novel Design of La(Fe,Si)13 Alloys Towards High Magnetic Refrigeration Performance.
Julia Lyubina 1 2 , Oliver Gutfleisch 2 , Ludwig Schultz 2 Show Abstract
1 Department of Materials, Imperial College London, London United Kingdom, 2 , IFW Dresden, Dresden Germany
Magnetic materials undergoing a first order magnetic phase transition are attractive candidates for use as magnetic refrigerants. However, these materials usually possess magnetic and thermal hysteresis and are prone to fracture as a result of crystal symmetry and/or volume change accompanying the transition. This reduces the efficiency or even makes the refrigeration cycle impossible. Here, we present a novel approach to controlling the magnetocaloric effect (MCE) in these materials by introducing porosity . In particular, we show that LaFe13−xSix magnetic refrigerants with porous architecture do not degrade mechanically during cycling, and thus maintain their excellent cooling performance. This very significant improvement is attributed to partial removal of grain boundaries that restrain volume expansion in the bulk material. Removal of the constraints also leads to a desirable reduction of hysteresis in the field- and thermally induced magnetic phase transitions. It will be discussed how size-tuning can be used to further enhance the MCE in materials exhibiting first-order transitions. J. Lyubina, R. Schäfer, N. Martin, L. Schultz, O. Gutfleisch, Adv. Mater., in press (http://dx.doi.org/10.1002/adma.201000177).
12:00 PM - FF4.7
Comparison of Direct and Indirect Determinations of the MCE in MnFe(P,Ge)Compounds.
Ramon Burriel 1 , GaoFeng Wang 1 , Elias Palacios 1 , Nguyen Trung 2 , Ekkes Brueck 2 Show Abstract
1 Instituto de Ciencia de Materiales, CSIC - Universidad de Zaragoza, Zaragoza Spain, 2 Fundamental Aspects of Materials and Energy Group, TU Delft, Delft Netherlands
Compounds of general formula Mn2-yFeyP1-xGex have been reported to present high magnetocaloric parameters, allowing varying the transition temperature (Tc) and having a small thermal hysteresis (ΔThys). The heat capacity of Mn1.26Fe0.74P0.75Ge0.25 at fields between 0 T and 5 T have been measured in an adiabatic calorimeter. A very small hysteresis has been deduced from heating and cooling runs at zero field, and disappears on increasing the field. Entropy curves have been deduced from these measurements and the corresponding isothermal entropy change (ΔST) and adiabatic temperature change (ΔTS) upon application of magnetic field have been calculated.The value of ΔTS has been measured directly when changing the field with adiabatic isolation of the sample. Also ΔST has been determined through the direct measurement of the heat applied to maintain a constant temperature while changing the field.The results of ΔTS and ΔST from calorimetric and direct measurements coincide almost perfectly. They also agree quite well with the values derived from magnetic measurements previously reported. In spite of the first order transition, the small hysteresis of these compounds avoids the usual problems in the determination of these parameters that results frequently in unreal huge peaks of ΔST at Tc  and the irreversible entropy production at the transitions that makes the heat determinations slightly incorrect for the ΔST calculation. The small hysteresis is a required property for any practical application of the materials in magnetic cooling at fields economically available. N.T. Trung, Z.Q. Ou, T.J. Gortenmulder, O. Tegus, K.H.J. Buschow, and E. Brück, Appl. Phys. Lett. 94, 102513 (2009) L. Tocado, E. Palacios, and R. Burriel, J. Appl. Phys. 105, 93918 (2009)
FF5: Magneto Calorics and Magnetic Cooling V
Tuesday PM, November 30, 2010
Republic A (Sheraton)
2:30 PM - **FF5.1
Active Magnetic Regenerators: Impacts of Specific Heat and Magnetocaloric Effect.
Andrew Rowe 1 2 Show Abstract
1 Mech Eng, UVic, Victoria, British Columbia, Canada, 2 Institute for Integrated Energy Systems, University of Victoria, Victoria, British Columbia, Canada
A simplification of the coupled differential equations describing energy conservation in the solid and fluid of an AMR is used to enable an analytic solution. The resulting set of expressions for cooling power and magnetic work input are related to regenerator design choices. Parameters governing regenerator operation are extracted and used to examine the behavior of AMRs under idealized conditions and with real material properties. In particular, the impacts of field and temperature-dependent specific heat and magnetocaloric effect are investigated. Results are used to identify preferred material properties and layering compositions.
3:00 PM - **FF5.2
Magnetocaloric Effect in Mn & Fe Based Materials.
Ekkes Bruck 1 , Nguyen Trung 1 , Nguyen Dung 1 , Zhiqiang Ou 1 , Luana Caron 1 , Lian Zhang 1 Show Abstract
1 Applied Sciences, TU Delft, Delft Netherlands
Modern society relies on readily available refrigeration. Magnetic refrigeration has three prominent advantages compared to compressor-based refrigeration. First there are no harmful gasses involved, second it may be built more compact as the working material is a solid and third magnetic refrigerators generate much less noise . Recently a new class of magnetic refrigerant-materials for room-temperature applications was discovered [2, 3]. These new materials have important advantages over existing magnetic coolants: They exhibit a large magnetocaloric effect (MCE) in conjunction with a magnetic phase-transition of first order. This MCE is, larger than that of Gd metal, which is used in most demonstration refrigerators built to explore the potential of this evolving technology. Especially, materials based on transition elements like manganese and iron appear to be promising for industrial applications. However, if the first order phase-transition is accompanied by large thermal hysteresis, simple refrigeration cycles can not be employed. Also the determination of the MCE for these materials with large hysteresis appears not to be straightforward. For optimal performance of the magnetocaloric devices also the thermal conductivity and the response to mechanical stress need to be tested. We discuss how one may tailor materials to meet the requirements for large MCE in combination with other favorable properties. As the Curie temperature of transition-metal compounds can easily exceed room temperature it becomes feasible to use them also in power conversion applications. A promising field is the conversion of waste heat to electric power with devices without moving parts. REFERENCE  E. Brück, J. Phys. D-Appl. Phys. 38(2005) R381-R391  V.K. Pecharsky and K.A. Gschneidner, Phys. Rev. Lett.. 78(1997) 4494-4497 O. Tegus, et al., Nature. 415(2002) 150-152
3:30 PM - FF5.3
A Compact Magnetic Cooling System for Work at Room Temperature.
Mohamed Balli 1 , David Duc 1 , Cyril Mahmed 1 , Philippe Bonhote 1 , Osmann Sari 1 Show Abstract
1 Institute of Thermal Sciences and Engineering,, University of Applied Sciences of Western Switzerland, Yverdon-les-Bains, Vaud, Switzerland
Using magnetocaloric effect (MCE) materials as refrigerant, magnetic refrigeration is one of the most promising technologies to replace traditional systems. In this paper, we present our recent development on the magnetic cooling field. Based on the permanent magnets array, different prototypes were designed and built, taking into account the compactness, the market and the thermodynamic performances requirements. Aiming to increase the magnetic systems efficiency, many efforts were made to reduce the magnetic forces in the machine and to increase the magnetic field generated by the magnetic source. However, to reach a large temperature span between the hot and the cold sources, a modified Active Magnetic Refrigeration (AMR) cycle was adopted for our application. The cooling performances of the developed system will be given as a function of the magnetocaloric materials (Gd, LaFe13-xSix…etc.) and heat transfer fluids.
4:15 PM - **FF5.4
Development and Fundamental Characteristics of Prototype Magnetocaloric Heat Pumps.
Tsuyoshi Kawanami 1 , Shigeki Hirano 1 Show Abstract
1 Mechanical Engineering, Kobe University, Kobe Japan
The primary objective of this study is to discuss the optimum operating condition of magnetocaloric heat pumps according o the fundamental heat transfer characteristics in an active magnetic regenerator (AMR) bed. The AMR system has basically four sequential processes: magnetization, heat exchange fluid blow, demagnetization and fluid blow. The fundamental heat transport characteristics at the each processes of the AMR cycle is investigated minutely, and both the cooling power and the total system performance is evaluated when the system is running continuously.In addition to the fundamental investigation, we have developed a prototype of rotational magnetocaloric heat pump with compact component formation and uncomplicated control system. A performance evaluation has been conducted to obtain an optimum condition of practical operation. Operating parameters such as a heat transfer fluid flow rate, a rotational frequency and an initial temperature of the heat transfer fluid are examined and the maximum temperature span between the inlet and outlet of the heat transfer fluid is discussed. As a result, the optimum rotation frequency and flow rate to obtain the maximum temperature span between the inlet and outlet of the present magnetocaloric heat pump.
4:45 PM - FF5.5
Building Coherent Magneto-thermodynamic Properties of Magnetocaloric Materials.
Michel Risser 1 , Carmen Vasile 1 , Bernard Keith 1 , Thierry Engel 2 , Christian Muller 3 Show Abstract
1 LGeCo, INSA, Strasbourg, Alsace, France, 2 LSP, INSA, Strasbourg, Alsace, France, 3 , Cooltech Applications, Holtzheim, Alsace, France
The simulation of magnetocaloric refrigerating device behaviour needs a good description of the active material properties. The needed characteristics of the Magnetocaloric Material (MCM) are adiabatic temperature change, heat capacity and magnetization. Today, MCM data are often given as a function of the external magnetic field applied on the sample. Consequently, the simulated materials in a mathematic model have abnormal behaviour. Indeed, characteristics expressed as a function of the external field are magneto-thermodynamically non coherent because active material reacts to its internal field. Thus it becomes difficult to take into account the impact of the demagnetizing field. For this reason a good correlation between theoretical values and experimental results cannot be obtained for an Active Magnetic Regenerator (AMR). In this paper we are presenting an alternative way to obtain the magnetocaloric and magnetic characteristics of a material. In this case the characteristics can be expressed as a function of both internal and external applied magnetic field. This allows good magneto-thermodynamic simulated behaviour in a magnetic refrigerator. This characterisation is built on the knowledge of the zero magnetic field heat capacity of second-order phase transition materials such as gadolinium and gadolinium alloys, as well as on the direct measurement of adiabatic temperature change or magnetization. The heat capacity without any magnetization comes from a conventional adiabatic calorimeter. The demagnetizing field factor of the material sample or of the Active Regenerator complex structure is assessed by 3D Finite Element Method. Hence, conventional direct measurement of adiabatic temperature change as a function of the external magnetic field can be used by an inverse approach to calculate the heat capacity, adiabatic temperature change and magnetization as a function of the internal magnetic field. Moreover it is possible to use the direct measurement from a specific experimental device, which ensures zero demagnetizing field. These measurements will be integrated into the magneto-thermodynamic model. The concept of such an experimental device will be presented.Finally the data obtained are converted as function of the external magnetic field for geometry of MCM corresponding to an AMR. This allows a better correlation of the numerical model with the experimental results.
5:00 PM - FF5.6
Evaluation of Some Magnetocaloric Materials.
Karl Gschneidner 1 2 , Yaroslav Mudryk 1 , Vitalij Pecharsky 1 2 Show Abstract
1 Ames Laboratory, Iowa State University, Ames, Iowa, United States, 2 Department of Materials Science and Engineering, Iowa State University, Ames, Iowa, United States
The efficiency of a magnetic cooling device greatly depends upon magnetocaloric properties (the adiabatic temperature change and the magnetic entropy change) of the magnetic refrigerant. Both the entropy and temperature change are needed to determine the cooling capacity or refrigeration efficiency. Unfortunately, there is a paucity of adiabatic temperature change values. A number of materials for which all of these data exist are compared. In addition to magnetocaloric effect, other properties such as hysteresis, time dependence of phase transformation, structural integrity, fabrication into useful regenerator forms, etc. need to be considered because the magnetic refrigerants will be exposed to about trillion heating and cooling cycles at frequencies ranging from 0.5 to 10 Hz during the 15 to 20 year lifetime of a cooling machine. Solving some of the problems associated with materials’ properties and the lifetime reliability requirements offer a challenge and research opportunities for materials scientists and engineers. Today the leading magnetic refrigerant candidates are those materials that are ductile and have good magnetocaloric properties.