Abstract
We investigate spin orbit torque (SOT) efficiencies and magnetic properties of Pt/GdFeCo/MgO multilayers by varying the thicknesses of GdFeCo and MgO layers. Our studies indicate that the ferrimagnetism in the GdFeCo alloy is considerably influenced by both thicknesses due to the diffusion of Gd atoms toward the MgO layer. Comparing to conventional Pt/ferromagnet/MgO structures, the Pt/GdFeCo/MgO exhibits a lower efficiency of SOTs associated with ferrimagnetic order and a similar magnitude of magnetic damping. The previous models that have been developed for rigid ferromagnets are inappropriate to analyze our experimental data, leading to an unphysical consequence of spin transmission larger than unity. Our results imply that the heavy-metal/ferrimagnet system is quite different from heavy-metal/ferromagnet systems in terms of magnetic dynamical modes, spin angular momentum transfer, and relaxation processes.
Highlights
Significant amounts of works have demonstrated that spin-orbit torque (SOT) induced by in-plane current and strong spin-orbit coupling (SOC) can efficiently reorient the magnetization in heavy-metal/ferromagnet/oxide multilayers[1,2]
We have examined whether the previous models that have been developed for rigid ferromagnets can explain our experimental results with GdFeCo ferrimagnets
In our spin-torque ferromagnetic resonance (ST-FMR) measurements, the applied frequency range corresponds to the regular FMR mode, we interpret our results based on the analysis from the usual macrospin model/theory with the experimental γeff
Summary
JongHyuk Kim[1,2], DongJoon Lee[1,3], Kyung-Jin Lee 3,4, Byeong-Kwon Ju2, Hyun Cheol Koo 1,3, Byoung-Chul Min 1,5 & OukJae Lee[1]. We investigate spin orbit torque (SOT) efficiencies and magnetic properties of Pt/GdFeCo/MgO multilayers by varying the thicknesses of GdFeCo and MgO layers. Comparing to conventional Pt/ferromagnet/MgO structures, the Pt/GdFeCo/MgO exhibits a lower efficiency of SOTs associated with ferrimagnetic order and a similar magnitude of magnetic damping. We are interested in how the ferrimagnetic order in GdFeCo is related to the SOT efficiency, spin transparency, and magnetic damping. The measured SOT efficiencies of Pt/GdFeCo/MgO structures are smaller than those in conventional ferromagnetic layers, but the magnetic damping of the GdFeCo layer is similar to the magnitude of that in a conventional Pt/FM/MgO layer. A vibrating sample magnetometer (VSM) is used to measure the net magnetization (Ms = MFeCo − MGd) and the effective out-of-plane anisotropy field (Hkeff = 2Keff /Ms) of the un-patterned Pt/GdFeCo/MgO films at room temperature (RT). I2sπuas2u)atlGlydFeexCpo r−ess2eπdba2s/tKGdeFffetCGodF+eCo(K=S (KV − 2πMS2) tGdFeCo − 4πab) withth
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