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Giant Magnetostriction and Low Loss in FeGa/NiFe Laminates for Strain-Mediated Multiferroic Micro-Antenna Applications
Kevin Fitzell1,Joseph Schneider1,Jin-Zhao Hu1,Zhi Yao1,Colin Rementer1,Nishanth Virushabadoss2,Michelle Jamer3,Cunzheng Dong4,Anthony Barra1,Daniel Gopman3,Nian Sun4,Julie Borchers3,Brian Kirby3,Yuanxun Wang1,Rashaunda Henderson2,Abdon Sepulveda1,Gregory Carman1,Jane Chang1
University of California, Los Angeles1,The University of Texas at Dallas2,National Institute of Standards and Technology3,Northeastern University4
The ability to reduce the size of antennae would enable a revolution in wearable and implantable devices. Multiferroic antennae, composed of individual ferromagnetic and piezoelectric phases, are posed to reduce antenna size by up to 5 orders of magnitude through the efficient coupling of magnetization and electric polarization via strain. However, this strategy requires a low-loss magnetic material with strong magnetoelastic coupling at high frequency.
Galfenol (Fe84Ga16 or FeGa) is a promising candidate material due to its large magnetostriction (>200 ppm), large piezomagnetic coefficient (>3 ppm/Oe), and high stiffness (>50 GPa), but it is highly lossy in the GHz regime. On the other hand, Permalloy (Ni81Fe19 or NiFe) is a soft magnetic material that has very low loss in the GHz regime (ferromagnetic resonance linewidth <20 Oe) but almost no magnetostriction. In this work, nanoscale laminates containing alternating layers of FeGa and NiFe were fabricated via DC magnetron sputtering to combine their complementary properties, yielding a small coercive field (<20 Oe), narrow FMR linewidth (<40 Oe), and high relative permeability (>700) (Rementer et al., 2017). These magnetic laminates were then grown on PMN-PT substrates and studied via polarized neutron reflectometry, demonstrating coherent rotation of the individual layers’ magnetization with an applied electric field, supported by micromagnetic and finite element simulations (Jamer et al, 2018).
In addition, optical magnetostriction measurements confirmed the presence of greatly enhanced magnetostriction relative to single-phase FeGa; these laminates represent a threefold increase in magnetostriction at saturation (~700 ppm) and an enhanced sensitivity at low bias magnetic fields (25 ppm/Oe). This enhancement in magnetoelasticity relative to single-phase FeGa was correlated to the microstructure of these composites using TEM. Recent efforts have further enhanced the high-frequency properties of these composites through insertion of ultrathin Al2O3 layers to reduce the conductivity and mitigate eddy current losses, and subsequent integration of these laminates into a strain-mediated multiferroic shear wave antennae successfully demonstrated the great potential of FeGa/NiFe laminates for use in microscale communications systems.
1. C. R. Rementer, K. Fitzell, Q. Xu, et al., Applied Physics Letters, Vol. 110 (24), 242403 (2017)
2. M. E. Jamer, C. R. Rementer, A. Barra, A. J. Grutter, K. Fitzell, et al., Physical Review Applied, Vol. 10 (4), 044045 (2018)