Magnetic Insulators

Early breakthrough discoveries in spintronics, namely the giant and tunnel magnetoresistance effects, magnetic interlayer coupling, interfacial perpendicular magnetic anisotropy (PMA), and spin-transfer-torques (STT), exclusively relied on conducting magnetic materials such as Co, Fe, and Ni. Due to the lack of knowledge and methods to electrically probe and control magnetization, magnetic insulators remained less explored in the spintronics context up until recently.

Discoveries such as the spin Seebeck effect, spin pumping, and spin hall magnetoresistance have granted us the tools to generate and probe spin currents by actively using magnetic insulators in devices. More recently, we have achieved current-induced magnetization switching and domain wall motion in magnetic insulators by spin-orbit torques, just how it is done in conducting magnetic materials. With these recent advances, we are now on the verge of a paradigm shift in spintronics where insulating magnetic materials are becoming a major player. In MAGNEPIC, we investigate ferrimagnetic insulators. A ferrimagnet is in-between a ferromagnet and an antiferromagnet. The adjacent spins are aligned antiparallel to each other, like in an antiferromagnet, but these spins possess unequal magnetic moments, so the net magnetization is non-zero like in a ferromagnet. Because one can greatly vary the forming elements and their relative compositions in a ferrimagnetic insulator, they offer multiple tuning knobs to adjust their magnetic properties. Some ferrimagnetic insulators of interest to this project are thulium iron garnet (Tm3Fe5O12, TmIG), terbium iron garnet (Tb3Fe5O12, TbIG), and yttrium iron garnet (Y3Fe5O12, YIG).