Spin accumulation dynamics in spin valves in the terahertz regime

• Published in: Physical review. B 2020-01, Vol.101 (1), p.1, Article 014401
• Main Authors: Vedyaev, A., Ryzhanova, N., Strelkov, N., Lobachev, A., Dieny, B.
• Format: Article
• Language: English
• Subjects: Accumulation; Antiferromagnetism; Elastic scattering; Ferrimagnetism; Frequency ranges; Giant magnetoresistance; Magnetoresistance; Magnetoresistivity; Multilayers; Physics; Relaxation time; Spin dynamics; Spin valves
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.101.014401

The notion of spin accumulation and spin relaxation in the diffusive regime was introduced by Valet and Fert in 1993 to describe the current-perpendicular-to-plane (CPP) diffusive transport in metallic magnetic multilayers. This theory has been quite successful in explaining the giant magnetoresistance of magnetic multilayers in CPP geometry in the frequency range from DC to a few gigahertz. In this paper, we investigate the dynamic aspect of spin accumulation from the theoretical point of view when reaching the terahertz (THz) frequency range. The characteristic relaxation time of electron elastic scattering is typically in the femtosecond range. However, since spin accumulation results from a diffusion process involving a very large number of individual scattering events, the characteristic time of spin accumulation variation when the current and/or the magnetic configuration are varied can be significantly longer than that of the input signal, eventually reaching the picosecond range. In spintronic devices operating in the THz range such as those based on ferrimagnetic or antiferromagnetic materials, the spin accumulation amplitude and, correlatively, the device magnetoresistance can therefore depend on the actual device operating frequency. We investigate this question by extending the Valet and Fert theory in the time domain.