Switching, Torques, and Spin Transport in Magnetic Insulators with Perpendicular Anisotropy

Magnetic insulators (MIs), especially iron-based garnets, possess remarkable properties such as ultralow damping and long magnon decay lengths, which can provide significant advantages for practical applications with respect to their metallic magnetic counterparts. Recently, robust perpendicular magnetic anisotropy is obtained in ferrimagnetic films of thulium, europium, and terbium iron garnet (TmIG, EuIG and TbIG) with high structural quality down to a thickness of 5.6 nm with saturation magnetization close to bulk [1]. By using the spin Hall effect in platinum we have demonstrated efficient spin current injection through the TmIG/Pt interface, which we quantified by the spin Hall magnetoresistance and harmonic Hall effect measurements [2,3]. We then achieved deterministic spin-orbit torque-driven magnetization switching of TmIG(~10 nm)/Pt bilayer both with quasi-dc (5 ms) as well as pulsed currents down to 2 ns width[3,4]. The switching current density is found to be of the order of ~10⁷ (~10⁸) A/cm² using dc (pulsed) current, comparable to reported values for Pt/Co[5]. We reveal that the threshold switching current strongly depends on the absence or presence of an initially reversed domain in the structure implying a reversal mediated by efficient current-driven domain wall motion. Based on this hypothesis we estimate the current-driven domain wall velocity ~400 m/s per j=10⁸A/cm², exceeding the most efficient domain wall velocities reported in metallic ferromagnets[6]. These results suggest the utility of PMA rare earth garnets and pave the road towards ultralow dissipation spintronic devices based on MIs.
[1]Quindeau et al., Adv. Elec. Mater. 3, 1600376 (2017); [2]Avci et al., Nat. Mater. 16, 309 (2017); [3]Avci et al., PRB 95, 115428 (2017); [4]Avci et al., APL 111, 072406 (2017); [5]Miron et al., Nature 476, 189 (2011); [6]Yang et al., Nat. Nano. 10, 221 (2015)