Presentation Information
[10p-PA3-29]Spin-torque ferromagnetic resonance measurement in Fe4-xCoxN/Ti bilayer systems
〇Hiroki Kunieda1, Shoya Sakamoto2,3, Keita Ito2, Takeshi Seki2,3,4 (1.Grad. Sch. Eng., Tohoku Univ., 2.IMR, Tohoku Univ., 3.CSIS, Tohoku Univ., 4.SRIS, Tohoku Univ.)
Keywords:
orbital torque,nitride,magnetostriction
Previous studies suggested that the orbital torque depends on the spin-orbit coupling (SOC) in the ferromagnet layer. However, the detailed mechanism of how an orbital Hall effect-injected orbital current exerts torque on spins remains unclear. In this study, we investigate the relationship between magnetostriction and orbital torque, both of which are quantities intimately related to SOC.
We focused on Fe4N thin films because their magnetostriction constants can be significantly tuned by substituting Co for Fe, allowing us to systematically investigate the orbital torque efficiency in Fe4-xCoxN/Ti bilayers. The samples were grown by molecular beam epitaxy with the stack structure: MgO(001) substrate/Fe4-xCoxN (4 nm) (x = 0, 0.5, 2.0)/Ti (5 nm)/CaF2 (5 nm)/SiO2 (3 nm). The torque efficiencies of each sample were characterized by spin-torque ferromagnetic resonance (STFMR) measurements.
The obtained STFMR spectra were fitted using a combination of symmetric and antisymmetric Lorentzian functions, where their ratio Vs/Va reflects the torque efficiency. The effective magnetization values were consistent with the saturation magnetization, except for the Fe2Co2N/Ti sample. When the microwave current was applied along the MgO [100] direction, Vs/Va exhibited finite values for x = 0 and 0.5 but almost vanished for x = 2.0. In contrast, when the microwave current was applied along the MgO [110] direction, the Vs/Va values were negligibly small regardless of the Co content. This crystal orientation dependence suggests the anisotropic nature of orbital torque. In the presentation, the relationship between orbital torque and magnetostriction will be discussed.
We focused on Fe4N thin films because their magnetostriction constants can be significantly tuned by substituting Co for Fe, allowing us to systematically investigate the orbital torque efficiency in Fe4-xCoxN/Ti bilayers. The samples were grown by molecular beam epitaxy with the stack structure: MgO(001) substrate/Fe4-xCoxN (4 nm) (x = 0, 0.5, 2.0)/Ti (5 nm)/CaF2 (5 nm)/SiO2 (3 nm). The torque efficiencies of each sample were characterized by spin-torque ferromagnetic resonance (STFMR) measurements.
The obtained STFMR spectra were fitted using a combination of symmetric and antisymmetric Lorentzian functions, where their ratio Vs/Va reflects the torque efficiency. The effective magnetization values were consistent with the saturation magnetization, except for the Fe2Co2N/Ti sample. When the microwave current was applied along the MgO [100] direction, Vs/Va exhibited finite values for x = 0 and 0.5 but almost vanished for x = 2.0. In contrast, when the microwave current was applied along the MgO [110] direction, the Vs/Va values were negligibly small regardless of the Co content. This crystal orientation dependence suggests the anisotropic nature of orbital torque. In the presentation, the relationship between orbital torque and magnetostriction will be discussed.