CURRENT-INDUCED SPIN-ORBIT TORQUE IN ANTIFERROMAGNETIC IRIDIUM MANGANESE

Abstract

Spin-orbit torque (SOT) offers promising approaches to developing energy-efficient memory devices by electric switching of magnetization. Comparing to other SOT materials, metallic antiferromagnet potentially allows the control of SOT through its magnetic structure. In this thesis, we systematically study the crystal and magnetic structures of IrMn in three phases, namely the γ, L10 and L12 phases. Single-crystal IrMn exhibits distinct phase-dependent SOT efficiencies that are substantially larger than the polycrystalline films. Moreover, we show that the room-temperature magnetic structure of epitaxially grown L10-IrMn is distinct from the widely presumed bulk one. Its unconventional magnetic structure induces a large isotropic bulk contribution to the SOT efficiency and an anisotropic interfacial contribution of comparable magnitude, where the latter depends strongly on the electric current direction in the film plane. Our findings sheds light on the critical roles of bulk and interfacial antiferromagnetism to SOT generated by metallic antiferromagnets.