Parametric Amplification of Magnons in Synthetic Antiferromagnets

Abstract

Non-linear interactions related to magnons are expected to be applied to advanced computing devices [1,2]. Synthetic antiferromagnets (SAFs) are candidate materials to observe non-linear magnon interactions because they have two fundamental magnon modes, that are the acoustic (AC) and optical (OP) modes [3]. However, there are no reports whether the AC and OP mode can interact with each other. Here, we report parametric amplification of the AC mode by the OP mode in SAFs using time-resolved magneto-optical Kerr effect (TRMOKE) technique [4]. SAF films, Si/SiO2 (subs.)/Ta(3)/Co20Fe60B20(3)/Ru(0.4)/Co20Fe60B20(3)/Ta(3) (thickness is in nm), was prepared by a sputtering. Fig. 1(a) shows the TRMOKE data with various pump laser power Ppump at the critical magnetic field angle θH,c . At this angle, 2fAC = fOP is satisfied, where fAC and fOP are the frequency of the AC and OP mode, respectively. ΔθK and Δt are the change in the Kerr rotation angle and the pump-probe delay time, respectively. In case of Ppump > 5 mW, the temporal amplification of the magnetization precession was observed (dashed curves). Fig. 1(b) shows the θH dependence of the peak intensity of the FFT spectrum at the Ppump = 10 mW for the AC and OP mode, respectively. At around θH = 45°~ θH,c , the intensity of the AC mode rapidly enhanced. This indicates the non-linear interaction between the AC and OP modes is allowed for SAFs. The threshold of the OP mode to the amplification will be also discussed. This work was partially supported by KAKENHI (Nos. 26103004 and 19K15430). A.K. thanks to GP-Spin at Tohoku University.