Novel Spin–Orbit Torque Generation at Room Temperature in an All‐Oxide Epitaxial La_0.7Sr_0.3MnO₃/SrIrO₃ System

Abstract

Spin–orbit torques (SOTs) that arise from materials with large spin–orbit coupling offer a new pathway for energy‐efficient and fast magnetic information storage. SOTs in conventional heavy metals and topological insulators are explored extensively, while 5d transition metal oxides, which also host ions with strong spin–orbit coupling, are a relatively new territory in the field of spintronics. An all‐oxide, SrTiO3 (STO)//La0.7Sr0.3MnO3 (LSMO)/SrIrO3 (SIO) heterostructure with lattice‐matched crystal structure is synthesized, exhibiting an epitaxial and atomically sharp interface between the ferromagnetic LSMO and the high spin–orbit‐coupled metal SIO. Spin‐torque ferromagnetic resonance (ST‐FMR) is used to probe the effective magnetization and the SOT efficiency in LSMO/SIO heterostructures grown on STO substrates. Remarkably, epitaxial LSMO/SIO exhibits a large SOT efficiency, ξ|| = 1, while retaining a reasonably low shunting factor and increasing the effective magnetization of LSMO by ≈50%. The findings highlight the significance of epitaxy as a powerful tool to achieve a high SOT efficiency, explore the rich physics at the epitaxial interface, and open up a new pathway for designing next‐generation energy‐efficient spintronic devices.

High‐Efficiency Magnon‐Mediated Magnetization Switching in All‐Oxide Heterostructures with Perpendicular Magnetic Anisotropy

“…We chose SIO based on theoretical predictions of strong SOC capable of generating an intrinsic spin Hall effect. [28][29][30][31][32] The spin Hall conductivity of SIO is reported to be in the range of 0.4-1.1, [28,[31][32][33][34] which is much larger than that of Pt. Ever since NiO was first shown to be an excellent magnon host, it has been widely used as an intermediate insulating antiferromagnetic layer.…”

“…The first is the large spin Hall angle of the epitaxial SIO layer, which is reported to be in the range of 0.4-1.1. [31][32][33] The second is the large spin transparency T int of the epitaxial interface. Since T int is mainly dominated by the spin backflow and spin memory loss at the interface, [58][59][60] the high-quality interface which can suppress the spin backflow and spin memory loss should favor a large T int .…”

“…For example, Huang et al had reported that the atomically sharp interface between ferromagnetic La 0.7 Sr 0.3 MnO 3 and metallic SIO layers exhibited a highly efficient charge-to-spin conversion. [32] In addition, we also studied magnetization switching in samples with various SIO layer thicknesses. In particular, we noticed that although the J C value increased rapidly with decreasing SIO layer thickness, the critical switching current I C seemed to be independent of the thickness (Figure S13, Supporting Information).…”

“…For example, Huang et al had reported that the atomically sharp interface between ferromagnetic La 0.7 Sr 0.3 MnO 3 and metallic SIO layers exhibited a highly efficient charge‐to‐spin conversion. [ 32 ]…”

Spin Mixing Conductance at the Iridate–Manganite Interface

“…Note,  g Re =1.3 10 18 m -2 was obtained in [44] for the SIO/LSMO heterostructure fabricated by laser ablation. According to [45], when the SIO film thickness changes from 1.5 to 12 nm Re  g for SIO/LSMO heterostructure changes from 0.5 to 3.6 10 19 m -2 respectively. Theory based on the spin-exchange interaction between localized moments and conductivity electrons shows that the deterministic material properties for  g Re are the electrical resistivity ρSIO and the spin diffusion length λSIO of N metal [40,46,47] :…”