Spin Orbit Torques and Proximity-induced Magnetism in Thulium Iron Garnet Heterostructures
Iron garnets with composition R3Fe5O12 are ferrimagnetic insulators (FMIs) whose magnetic properties can be modified by R-site substitution. Y3Fe5O12 (YIG) is the most widely studied magnetic garnet, but YIG films typically exhibit in-plane magnetization dominated by shape anisotropy. Here we describe the growth and spintronic properties of Tm3Fe5O12 (TmIG) films grown epitaxially on Gd3Ga5O12 (GGG) (111) substrates by pulsed laser deposition. TmIG (111) films exhibit perpendicular magnetic anisotropy (PMA) as a result of magnetocrystalline anisotropy plus a magnetoelastic contribution due to the in-plane tensile strain. MOKE, vibrating sample magnetometry and magnetic force microscopy confirm the presence of PMA, a near-bulk magnetization even for films as thin as 5.6 nm (5 unit cells), and coercivity as low as 18 Oe, and XMCD shows the ferrimagnetic configuration of the tetrahedral Fe and the Tm and octahedral Fe trivalent ions. Both anomalous Hall effect and charge-current-induced switching of the magnetization via spin orbit torque were demonstrated in heterostructures consisting of heavy metal/TmIG. Spin Hall magnetoresistance measurements indicate a high spin mixing conductance at the Pt/TmIG interface, and full bidirectional reversal of the magnetization of an 8 nm thick TmIG film was demonstrated at 1 – 2 x 10(11) A/m2 current density in Pt in the presence of a modest fixed in-plane field. TmIG/(Bi,Sb)2Te3 topological insulator (TI) heterostructures were also fabricated in which proximity-induced magnetism was detected in the TI using polarized neutron reflectometry. These results demonstrate the potential of a PMA FMI in revealing spintronic phenomena relevant to low-dissipation electronics.