| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Monday Sessions |
| Session TF+EM+MI+MN+OX+PS-MoM |
| Session: | Functional Thin Films: Ferroelectric, Multiferroics, and Magnetic Materials |
| Presenter: | Kevin Fitzell, University of California, Los Angeles |
| Authors: | K. Fitzell, University of California, Los Angeles A. Acosta, University of California, Los Angeles C.R. Rementer, University of California, Los Angeles D.J. Schneider, University of California, Los Angeles Z. Yao, University of California, Los Angeles C. Dong, Northeastern University M.E. Jamer, National Institute of Standards and Technology (NIST) D. Gopman, National Institute of Standards and Technology (NIST) J. Borchers, National Institute of Standards and Technology (NIST) B. Kirby, National Institute of Standards and Technology (NIST) N. Sun, Northeastern University Y. Wang, University of California, Los Angeles G.P. Carman, University of California, Los Angeles J.P. Chang, University of California, Los Angeles |
| Correspondent: | Click to Email |
The ability to reduce the size of antennae would enable a revolution in wearable and implantable electronic devices. Multiferroic antennae, composed of individual ferromagnetic and piezoelectric phases, could reduce antenna size by up to five orders of magnitude through the efficient coupling of magnetization and electric polarization via strain. This strategy requires a material with strong magnetoelastic coupling and acceptable magnetic losses at high frequency.
Galfenol (Fe84Ga16 or FeGa) is a promising candidate material due to its large magnetostriction (200 µε), large piezomagnetic coefficient (5 ppm/Oe), and high stiffness (60 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, with a ferromagnetic resonance (FMR) linewidth of 10 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 the complementary properties of the two magnetic phases, resulting in a composite material with a small coercive field, narrow FMR linewidth, and high permeability (Rementer et al., 2017). Optical magnetostriction measurements confirmed that these laminates retain the large saturation magnetostriction of FeGa (200 µε) while enhancing the piezomagnetic coefficient (7 ppm/Oe), allowing for optimal piezomagnetic actuation at substantially reduced magnetic bias fields. Furthermore, multiferroic composites incorporating these magnetic laminates were studied via polarized neutron reflectometry, demonstrating uniform rotation of the individual layers’ magnetization with an applied electric field across distances much larger than the exchange length of either material.
Due to the metallic nature of these FeGa/NiFe multilayer composites, however, resulting devices would be inefficient due to the generation of eddy currents at high frequency. To mitigate these losses, ultrathin layers of Al2O3 were incorporated into the multilayer materials to reduce the conductivity and mitigate the generation of eddy currents. The effect of Al2O3 thickness, FeGa:NiFe volume ratio, and multilayer architecture on the soft magnetic properties was also studied, resulting in a 50% reduction in the FMR linewidth. Optimized magnetic laminates were shown to exhibit a small coercive field (<20 Oe), narrow ferromagnetic resonance linewidth (<50 Oe), and high relative permeability (>500) while maintaining excellent magnetoelastic coupling, showing great promise for the use of FeGa/NiFe/Al2O3 laminates in strain-mediated micro-scale communications systems.