A fundamental form of magnon-phonon interaction is an intrinsic property of magnetic materials, the “magnetoelastic coupling.” This form of interaction has been the basis for describing magnetostrictive materials and their applications, where strain induces changes of internal magnetic fields. Different from the magnetoelastic coupling, more than 40 years ago, it was proposed that surface acoustic waves may induce surface magnons via rotational motion of the lattice in anisotropic magnets. However, a signature of this magnon-phonon coupling mechanism, termed magneto-rotation coupling, has been elusive. Here, we report the first observation and theoretical framework of the magneto-rotation coupling in a perpendicularly anisotropic film Ta/CoFeB(1.6 nanometers)/MgO, which consequently induces nonreciprocal acoustic wave attenuation with an unprecedented ratio of up to 100% rectification at a theoretically predicted optimized condition. Our work not only experimentally demonstrates a fundamentally new path for investigating magnon-phonon coupling but also justifies the feasibility of the magneto-rotation coupling application.
We demonstrate a spin to charge current conversion via magnon-phonon coupling and inverse Edelstein effect on the hybrid device Ni/Cu(Ag)/Bi2O3. The generation of spin current (Js ≈ 10 8 A/m 2 ) due to magnon -phonon coupling reveals the viability of acoustic spin pumping as mechanism for the development of spintronic devices. A full in-plane magnetic field angle dependence of the power absorption and a combination of longitudinal and transverse voltage detection reveals the symmetric and asymmetric components of the inverse Edelstein effect voltage induced by Rayleigh type surface acoustic waves. While the symmetric components are well studied, asymmetric components are widely unexplored. We assign the asymmetric contributions to the interference between longitudinal and shear waves and an anisotropic charge distribution in our hybrid device.
We report the direct observation of uniform in-plane spin accumulation at room temperature by magneto optical Kerr effect, at the interface formed between nonmagnetic metal (Cu, Ag) and oxide (Bi2O3). Recent reports show spin to charge conversion at these interfaces suggesting the presence of Rashba like spin orbit coupling (SOC). The formation of spin accumulation is the result of current induced spin polarization at our interfaces (direct Rashba–Edelstein effect), without external magnetic field or proximity to ferromagnetic materials. We observe opposite orientation of spin accumulation at Cu/Bi2O3 and Ag/Bi2O3 interfaces reflecting their opposite sign of Rashba SOC (Rashba parameter). Moreover, estimation of spin accumulation from values of Rashba parameters obtained by independent spin pumping measurements, agrees well with the difference in amplitude of our normalized Kerr signals for Cu/Bi2O3 and Ag/Bi2O3 interfaces. Uniform in-plane spin accumulation due to Rashba-Edelstein effect can be applied for spin filter devices and efficient driving force for magnetization switching.
Voltage induced magnetization dynamics of magnetic thin films is a valuable tool to study anisotropic fields, exchange couplings, magnetization damping and spin pumping mechanism. A particularly well established technique is the ferromagnetic resonance (FMR) generated by the coupling of microwave photons and magnetization eigenmodes in the GHz range. Here we review the basic concepts of the so-called acoustic ferromagnetic resonance technique (a-FMR) induced by the coupling of surface acoustic waves (SAW) and magnetization of thin films. Interestingly, additional to the benefits of the microwave excited FMR technique, the coupling between SAW and magnetization also offers fertile ground to study magnon-phonon and spin rotation couplings. We describe the in-plane magnetic field angle dependence of the a-FMR by measuring the absorption / transmission of SAW and the attenuation of SAW in the presence of rotational motion of the lattice, and show the consequent generation of spin current by acoustic spin pumping.PACS numbers:
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