UCLA

In this thesis, we focus on designing new material systems that could help reduce Ohmic loss to enable future, low-power electro-magnetic devices. The first part of this thesis details voltage-control magnetism, which contrasts to conventional current-controlled magnetism. We specifically investigate strain-mediated magnetoelectric composites, which couple a ferroelectric material that strains in response to a voltage, to a magnetostrictive material, which changes magnetization in response to strain. We introduce a new category of magnetoelectric nanocomposites with residual porosity engineered into them. In the synthesis, block-copolymer templating is used to create a porous ferromagnetic framework, and then atomic layer deposition (ALD) is used to partly coat the inside of the pores with ferroelectric material. Residual porosity increases the mechanical flexibility of the composites, and thus allows for more fully-realized magnetoelectric coupling than conventional layered composites. Thus, we find large (> 50 %) changes in magnetization in samples with the most residual porosity.While the first part of this thesis focuses on making nanostructured magnetoelectric materials, the second part of this thesis discusses our work in building new bulk/thin-film spintronic materials. For the ideal spintronic device material, low magnetic loss and high magnetostriction are desirable, but spin-orbit coupling prevents both from occurring in the same material. Here we study systems based on yttrium iron garnet (YIG), a low magnetic loss material, and dope them to increase their magnetostriction. Using sol-gel chemistry, we surveyed a range of dopant stoichiometries of Ce:YIG and Ru:YIG, and made the exciting discovery that Ru:YIG films actually exhibit lower Gilbert damping than undoped YIG, which has previously been predicted by Kittel. Since inhomogeneous broadening is quite large in these polycrystalline films due to magnon scattering at grain boundaries, we turned to polymer-assisted deposition, a solution-based method that allows for the deposition of epitaxial films. Interestingly, we found that Ru:YIG films grown on (111) GGG exhibited perpendicular magnetic anisotropy, which necessitates high magnetostriction. Furthermore, these films were found to have lower damping than undoped YIG, echoing previous findings in sol-gel films. Thus, we have shown that low-cost solution-phase methods can be used to produce high-magnetostriction, low-magnetic-loss materials for potential spintronic applications.