The generation of spin currents by thermal gradients applied to a magnetic film is known as the spin Seebeck effect (SSE). The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film produced by the spin to charge current conversion through the inverse spin Hall effect (ISHE). The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin orbit coupling, such as platinum. Recently, the SSE has been observed in bilayers made of the antiferromagnets MnF2 and Cr2O3 with Pt at low temperatures and high magnetic fields. Here, we report measurements of the SSE at room temperature and low magnetic fields in bilayers made of well textured films of antiferromagnetic NiO with several metals. The detection of the spin current generated by the thermal gradient in the NiO layer is made by means of the ISHE in the nonmagnetic metals Pt and Ta, in the AF metal IrMn, and in the ferromagnetic metal Ni81Fe19 (permalloy). The measured spin Seebeck effect in NiO/Pt has the same sign and is about one order of magnitude smaller than in YIG/Pt.
The intermetallic antiferromagnetic compound Mn2Au has been attracting considerable interest for antiferromagnetic spintronics due to its high Néel temperature and strong spin–orbit coupling. We report on the experimental investigation of the zero-wave number magnon frequencies in Mn2Au films using Brillouin and Raman inelastic light scattering techniques. The derived effective anisotropy field values are in close agreement with theoretical calculations. With the values of the anisotropy and exchange fields, the full magnon dispersion curves in Mn2Au were calculated. Due to the weak in-plane anisotropy, the k ∼ 0 frequency of the lower magnon branch, 121 GHz, is among the lowest for 3D antiferromagnets, suggesting that Mn2Au is a good candidate for realizing the generation of spin currents by antiferromagnetic resonance driven spin-pumping, as proposed theoretically.
Spin current phenomena are at the heart of the active research field of spintronics that aims to develop new perspectives for emerging information technologies. In recent years, several groups reported experiments in which spin currents are used to excite coherent magnetization dynamics in magnetic nanostructures. Here, we show experimentally two effects of the large spin current generated by the giant spin Hall effect in a platinum strip with nanoscopic silver particles adjacent to a film of the insulating ferrimagnet yttrium iron garnet (YIG). The first, demonstrated by ferromagnetic resonance (FMR) experiments, is the dramatic reduction of the magnon damping measured by the FMR linewidth due to the spin torque produced by the spin current. The second, observed by Brillouin light scattering (BLS), is the excitation of quasi-particles in the YIG film with frequencies that do not vary with the applied magnetic field. We interpret the BLS signal as due to phonons excited by the magnonic spin current injected into the YIG film, in a process that is the Onsager reciprocal of the spin pumping by coherent elastic waves.
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