Large spin-orbit torque efficiency enhanced by magnetic structure of collinear antiferromagnet IrMn

Abstract

Spin-orbit torque (SOT) offers promising approaches to developing energy-efficient memory devices by electric switching of magnetization. Compared to other SOT materials, metallic antiferromagnet (AFM) potentially allows the control of SOT through its magnetic structure. Here, combining the results from neutron diffraction and spin-torque ferromagnetic resonance experiments, we show that the magnetic structure of epitaxially grown L10-IrMn (a collinear AFM) is distinct from the widely presumed bulk one. It consists of twin domains, with the spin axes orienting toward [111] and [−111], respectively. This unconventional magnetic structure is responsible for much larger SOT efficiencies up to 0.60 ± 0.04, compared to 0.083 ± 0.002 for the polycrystalline IrMn. Furthermore, we reveal that this magnetic structure induces a large isotropic bulk contribution and a comparable anisotropic interfacial contribution to the SOT efficiency. Our findings shed light on the critical roles of bulk and interfacial antiferromagnetism to SOT generated by metallic AFM.

Magnetic asymmetry induced anomalous spin-orbit torque in IrMn

“…In our previous report we found the staggered magnetic moments in L10-IrMn (001) films align with the [111] direction [22], as illustrated in Fig. 1(a).…”

“…The ST-FMR measurement was modulated using a sine function of low frequency. The modulated Vmix was collected using a lock-in amplifier and fitted using [4,8,22]…”

“…In Eq. 1 The SOT efficiency, ∥,m , which represents the magnitude of measured ∥ relative to ⊥ , can be extracted using [4,8,22]…”

“…Thin films of AFM, in general, are likely to be multi-domain in their ground states [23][24][25][26]. In our previous study [22], even we managed to obtain a high-quality epitaxial film, L10-IrMn still appeared as a twin-domain structure, which would have eliminated the differences between ∥ ℳ′ and ⊥ ℳ′. Therefore, the SOT induced by the broken ℳ′ has to be evaluated otherwise.…”

Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet

“…Despite a lack of clarity concerning the microscopic mechanisms of the Néel vector switching, these experiments have been widely regarded as a breakthrough in the emerging field of THz spintronics 26,30,36,[39][40][41][42][43] . It has been suggested that current-induced Néel vector dynamics in an AFM is driven primarily by the so-called Néel spin-orbit torques 29,32,[44][45][46][47][48][49][50][51][52][53][54][55][56] . The Néel spin-orbit torque originates in a non-equilibrium staggered polarization of conduction electrons on AFM sublattices 29,32,48,50 .…”