Anisotropic Gigahertz Antiferromagnetic Resonances of the Easy-Axis van der Waals Antiferromagnet CrSBr.

We report measurements of antiferromagnetic resonances in the van der Waals easy-axis antiferromagnet CrSBr. The interlayer exchange field and magnetocrystalline anisotropy fields are comparable to laboratory magnetic fields, allowing a rich variety of gigahertz-frequency dynamical modes to be accessed. By mapping the resonance frequencies as a function of the magnitude and angle of applied magnetic field, we identify the different regimes of antiferromagnetic dynamics. The spectra show good agreement with a Landau-Lifshitz model for two antiferromagnetically coupled sublattices, accounting for interlayer exchange and triaxial magnetic anisotropy. Fits allow us to quantify the parameters governing the magnetic dynamics: At 5 K, the interlayer exchange field is µ0HE = 0.395(2) T, and the hard and intermediate-axis anisotropy parameters are µ0Hc = 1.30(2) T and µ0Ha = 0.383(7) T. The existence of within-plane anisotropy makes it possible to control the degree of hybridization between the antiferromagnetic resonances using an in-plane magnetic field.

Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque.

Sagnac interferometry can provide a substantial improvement in signal-to-noise ratio compared to conventional magnetic imaging based on the magneto-optical Kerr effect. We show that this improvement is sufficient to allow quantitative measurements of current-induced magnetic deflections due to spin-orbit torque even in thin-film magnetic samples with perpendicular magnetic anisotropy, for which the Kerr rotation is second order in the magnetic deflection. Sagnac interferometry can also be applied beneficially for samples with in-plane anisotropy, for which the Kerr rotation is first order in the deflection angle. Optical measurements based on Sagnac interferometry can therefore provide a cross-check on electrical techniques for measuring spin-orbit torque. Different electrical techniques commonly give quantitatively inconsistent results so that Sagnac interferometry can help to identify which techniques are affected by unidentified artifacts.

Novel Spin-Orbit Torque Generation at Room Temperature in an All-Oxide Epitaxial La0.7 Sr0.3 MnO3 /SrIrO3 System.

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)//La0.7 Sr0.3 MnO3 (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.