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technical paper
Enhancement of current to spin current conversion efficiency in synthetic antiferromagnetic layer system
Current-induced spin-orbit torque (SOT) originating from the spin-Hall effect (SHE) has attracted attention due to their potential applications for SOT-MRAM, skyrmion and domain wall devices. For their applications, heavy metal with high spin Hall angle (|θSH|) and low resistivity (ρxx) is necessary for an efficient SOT operation. We have proposed Co/Pt/(Ir or Ru)/Pt/Co synthetic antiferromagnetic (AF) systems for SOT-MRAM (Fig. 1), and found that the Pt/Ir/Pt spacer layer exhibits AF interlayer exchange coupling (Jex) as well as large || and low ρxx 1, 2.
In this study, we study the current-induced SOT in perpendicularly magnetized Co/Pt/Ir/Pt/Co synthetic AF system which exhibits nearly compensated magnetization. The synthetic AF structures with various Pt, Ir and Co layer thicknesses were prepared by using UHV sputtering system. The stacks were patterned into Hall bar devices and magnitude of the was evaluated from the shift of the reversal magnetic field due to the SOT current. The results were compared with those of the ferromagnetic stack systems with Co/Pt and Co/Pt/Ir-multilayer structures.
Figures 2(a) and 2(b) show the typical current-induced SOT switching under various fixed external magnetic fields (Hy) in Sample A (Co/Pt structure) and Sample B (synthetic AF structure), respectively. The magnetizations of the two Co layers in the synthetic AF can be switched between two anti-parallel states simultaneously by SOT. The estimated values of current density () at Hy=0 mT for Samples A and B are 7.9×107 and 4.2×107 A/cm2, respectively 3. The magnitude of in Sample B is about half that in Sample A. The magnitudes of estimated |θSH| for Samples A and B are 7.0% and 15.6%, respectively 3, which is consistent with SOT switching behavior (Fig. 2). In this presentation, we will also show the dependence of the magnitude of SHE on the strength of Jex in the synthetic AF system. This work was supported by the CIES Consortium, Spin-RNJ, RIEC, JST OPERA (JPMJOP1611), MEXT Next generation X-nics and JSPS KAKENHI (JP19H00844, JP21K18189).
References 1 Y. Saito, N. Tezuka, S. Ikeda and T. Endoh, Phys. Rev. B 104,064439 (2021). 2 Y. Saito, S. Ikeda and T. Endoh, Appl. Phys. Lett. 119, 142401 (2021). 3 Y. Saito, S. Ikeda and T. Endoh, Phys. Rev. B 105, 054421 (2022).