| Summary: | This thesis aims to develop materials for spintronic memories and demonstrate growth of iron garnet superlattices with layering at a sub unit cell scale. Iron garnet films are suitable for next generation spintronic memories because of their low Gilbert damping and their growth with perpendicular magnetic anisotropy (PMA) which promote fast domain wall dynamics. Additionally, selection of rare earth ion and substitution of cations in various sublattices of iron garnets enables tuning of their saturation magnetization, magnetocrystalline anisotropy, Gilbert damping and magnetostriction. Superlattices of garnets provide an opportunity to explore interfacial phenomena.
We first study spin transport in platinum/scandium-substituted terbium iron garnet heterostructures. Epitaxial scandium-substituted terbium iron garnet (TbScIG) thin films were deposited on gadolinium gallium garnet [GGG, (111) orientation] substrates using pulsed laser deposition (PLD). Sc, a nonmagnetic cation, occupies up to 40% of the octahedral Fe sites. Anomalous Hall effect-like spin Hall magnetoresistance measurements were performed to determine the effect of scandium content on spin mixing conductance of the TbScIG|Pt interface. The spin mixing conductance increased significantly with an increase in Sc content. We then study bilayer films of bismuth-substituted yttrium iron garnet (BiYIG)/thulium iron garnet (TmIG) grown on garnet substrates that combine the non-zero interfacial Dzyaloshinskii–Moriya interaction (DMI) of TmIG with moderate damping between that of BiYIG and TmIG, making them useful for the development of high speed spin orbit torque driven magnetic devices. Lastly, we describe superlattices made from rare earth (RE = Tm, Tb, Lu) and bismuth iron garnets (IGs) grown by pulsed laser deposition. Superlattices of TmIG/TbIG show a composition modulation for layers as thin as 0.45 nm, less than one unit cell, and exhibit perpendicular magnetic anisotropy that is qualitatively different from the in-plane anisotropy of the solid solution (Tm,Tb)IG. BiIG/LuIG superlattices exhibit magnetic damping characteristic of the end members rather than the solid solution. Garnet superlattices may provide a playground for exploring interface physics within a vast parameter space of cation coordination and substitution.
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