Antiferromagnets having negligible net magnetization but a topologically nontrivial spin structure are a good testbed for investigating the intrinsic anomalous Hall effect (AHE). In this Letter, we explore L12-ordered Mn3Ir thin films, which are one of the noncollinear antiferromagnets predicted to exhibit the intrinsic AHE due to their topologically nontrivial spin structure. The anomalous Hall conductivity as large as σAHE = 40 Ω−1 cm−1 was observed at R.T. This value can be translated to the anomalous Hall conductivity per net magnetization M as |σAHE/M| = 0.6 V−1, which is much larger compared to those for general ferromagnetic materials. We also show that σAHE depends on the crystallinity of Mn3Ir as well as the chemical order parameter S characterizing a content of the L12 phase. Our results experimentally verify that L12-ordered Mn3Ir thin films exhibit the topologically originated AHE.

We provide a macroscopic theory and experimental results for magnetic resonances of antiferromagnetically-coupled ferrimagnets. Our theory, which interpolates the dynamics of antiferromagnets and ferromagnets smoothly, can describe ferrimagnetic resonances across the angular momentum compensation point. We also present experimental results for spintorque induced ferrimagnetic resonance at several temperatures. The spectral analysis based on our theory reveals that the Gilbert damping parameter, which has been considered to be strongly temperature dependent, is insensitive to temperature. We envision that our work will facilitate further investigation of ferrimagnetic dynamics by providing a theoretical framework suitable for a broad range of temperatures.

Spin current transmission in antiferromagnetic materials is one of the important and intriguing problems in the recently emerged field of antiferromagnetic spintronics. We investigate the spin current transmission in polycrystalline NiO by referencing the effective Gilbert damping constant in NiO/FeNi bilayers. The results are discussed with reference to the spin pumping theory assuming that the NiO layer is spin diffusive. We extracted the spin diffusion length of ∼22 nm for the NiO and the mixing conductance of ∼6 nm−2 at the NiO/FeNi interface. The obtained spin diffusion length and the mixing conductance are within reasonable ranges compared with previous reports.