Abstract
The generation of significant spin imbalance in nonmagnetic semiconductors is crucial for the functioning of many spintronic devices, such as magnetic diodes and transistors, spin-based logic gates, and spin-polarized lasers. An attractive design of spin injectors into semiconductors is based on spin pumping from a precessing ferromagnet, but the classical excitation of magnetization precession by a microwave magnetic field leads to the high-power consumption of the device. Here, we describe theoretically a spin injector with greatly reduced energy losses, in which the magnetic dynamics is excited by an elastic wave generated in a ferromagnet-semiconductor heterostructure by an attached piezoelectric transducer. To demonstrate the efficient functioning of such an injector, we first perform micromagnetoelastic simulations of the coupled elastic and magnetic dynamics in films and bilayers traversed by plane longitudinal and shear waves. For thick films, it is shown that a monochromatic acoustic wave generates a spin wave with the same frequency and wavelength, which propagates together with the driving wave over distances of several micrometers at excitation frequencies GHz close to the frequency of ferromagnetic resonance. The simulations of bilayers with thicknesses comparable to the wavelength of the injected acoustic wave demonstrate the development of a steady-state magnetization precession at the interface. The amplitude of such a precession has a maximum at thickness amounting to three quarters of the wavelength of the elastic wave, which is explained by an analytical model. Using simulation data obtained for the magnetization precession at the interface, we evaluate the spin current pumped into and calculate the spin accumulation in the semiconducting layer by solving the spin diffusion equation. Then the electrical signals resulting from the spin flow and the inverse spin Hall effect are determined via the numerical solution of the Laplace's equation. It is shown that amplitudes of these ac signals near the interface are large enough for experimental measurement, which indicates an efficient acoustically driven spin pumping into and a rather high spin accumulation in this semiconductor.
3 More- Received 17 December 2020
- Accepted 15 April 2021
DOI:https://doi.org/10.1103/PhysRevMaterials.5.054601
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