Terahertz spin-transfer torque oscillator based on a synthetic antiferromagnet

Abstract

Bloch-Bloembergen-Slonczewski equation is adopted to simulate magnetization dynamics in spin-valve based spin-transfer torque oscillator with synthetic antiferromagnet acting as a free magnetic layer. High frequency up to the terahertz scale is predicted in synthetic antiferromagnet spin-transfer torque oscillator with no external magnetic field if the following requirements are fulfilled: antiferromagnetic coupling between synthetic antiferromagnetic layers is sufficiently strong, and the thickness of top (bottom) layer of synthetic antiferromagnet is sufficiently thick (thin) to achieve a wide current density window for the high oscillation frequency. Additionally, the transverse relaxation time of the free magnetic layer should be sufficiently larger compared with the longitudinal relaxation time. Otherwise, stable oscillation cannot be sustained or scenarios similar to regular spin valve-based spin-transfer torque oscillator with relatively low frequency will occur. Our calculations pave a new way for exploring THz spintronics devices.

Direct observation of magnetic process in quasi-antiferromagnet by high-resolution Kerr microscopy

“…15) However, it is challenging to observe a clear STO in AFMs for practical use because of the strong exchange stiffness coupling between adjacent magnetic moments. Although a THz STO is numerically expected in the synthetic antiferromagnetically coupled layers, 16) the frequency did not reach the THz region in an experiment. 17) Therefore, we fabricated a quasi-AFM with domains of alternating antiparallel magnetization, which exhibits FM coupling within one domain and AFM coupling between neighboring domains.…”

Spintronic terahertz emitters: Status and prospects from a materials perspective

“…142,143 SAF structures consist of two or more exchange-coupled ferromagnetic layers separated by metallic or dielectric spacer layers. [144][145][146] The interlayer exchange coupling in a SAF structure results from the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, 145,146 which is responsible for an oscillatory short-range interaction that can promote ferromagnetic (parallel) alignment or antiferromagnetic (antiparallel) alignment of the FM layers, depending on the spacer layer thickness, d s . 146,147 In 2020, Ogasawara et al 142 studied the emission of THz radiation from Ta (3 nm)/CoFeB (2 nm)/Ir (d s )/CoFeB (2 nm)/Ta (3 nm) synthetic (anti)ferromagnetic structures.…”

Biquadratic magnetic coupling effect in CoPt/Cr/Fe90Co10 orthogonal structures

“…In response to this challenge, artificial magnetic structures have been proposed as promising approaches for increasing the STO frequency. These structures encompass synthetic antiferromagnetic coupling layers [30][31][32] and quasi-antiferromagnets featuring biquadratic magnetic coupling, 33,34) offering a potential alternative for amplifying the STO frequency. In contrast, orthogonal magnetization multilayers, comprising magnetic layers with both in-plane and perpendicular magnetic anisotropies, have demonstrated high spin-transfer efficiency, rendering them suitable candidates for generating STOs with elevated frequencies and reduced power consumption.…”