Cation Ordering and Interfacial Engineering in Ferrimagnetic Iron Garnets

Iron garnets are ferrimagnetic insulators with iron cations occupying octahedral and tetrahedral sites and rare earths and other large cations in dodecahedral sites. They exhibit a range of useful magnetic properties including spin orbit torque switching, domain wall velocities of km/s, magnon-driven domain wall motion, and magnetooptical activity, making them useful in spintronic, magnonic and optical devices. Garnet films with mixed rare earths such as EuTmIG or BiYIG can exhibit a strong perpendicular anisotropy. We reveal the origin of this magnetotaxial anisotropy in the spontaneous ordering of cations on non-equivalent dodecahedral sites, and describe its dependence on composition, growth rate and annealing. By engineering the magnetoelastic, magnetotaxial, magnetocrystalline, surface and shape anisotropies of garnet films we obtain uncommon anisotropy landscapes such as an out-of-plane easy plane in (110)-oriented EuIG which enables spin orbit torque-driven magnetization precession. We describe the structure and unusual properties of epitaxial garnet bilayers and superlattices with layer thickness lower than one unit cell. We demonstrate how garnets and ferroelectric perovskites can be grown together on a patterned substrate to create multiferroic composites, and describe coupling between the two phases. Applications in spintronic devices and integrated nonreciprocal photonic devices will be described.