13:30 〜 15:30
▲ [14p-PA1-21] Influence of Oxygen content on the Gilbert damping constant at TaOx/CoFeB interface
キーワード：Damping constant, surface oxidized TaOx/CoFeB
Spin-orbit torque (SOT) induced magnetization switching in non-magnetic/ferromagnetic systems has attracted much attention for applications in spintronics devices [1,2]. Especially, a recent report on the SOT switching in oxide/ferromagnetic interfaces revealed a high spin-torque efficiency by tuning the surface oxidization [3]. However, a detail investigation of damping constant, which is one of the most important parameters to understand the magnetization switching in these systems, still remains unclear. Herein we evaluate damping constant of Ta-O/CoFeB stack films by a broadband ferromagnetic resonance (FMR) measurement technique, and discuss the influence of oxygen content on damping constant in these films in detail.
Ta-O (1 nm)/CoFeB (1.3 nm)/MgO (1.3 nm)/Ta (1nm) stack films were fabricated on thermally oxidized Si substrates by the RF sputtering at room temperature. Ta-O layers were formed by naturally oxidizing thin Ta layers at the different Oxygen pressure (P_Oxygen) of 0.3, 0.1, and 0.03 Pa. The post-annealing process was conducted at 250 and 350oC in a vacuum.
Figure 1 shows the dependence of damping constant and the interfacial anisotropy K_s on P_Oxygen for as-deposited and annealed stack films. K_s was evaluated by the equation: K_s = (4pM_s, eff - 4pM_s)x(tCFBM_s/2) where the saturation magnetization was measured by VSM (M_s) and FMR measurements(M_s, eff), respectively; and tCFB is the thickness of CoFeB layer. For every film, both damping constant and K_s decrease as P_Oxygen increases, suggesting that these parameters correlated with each other [4]. On the other hand, the rate of the enhancement of the damping constant by annealing in every oxidized film (Ta-O/CoFeB/MgO/Ta) is lower than that in the non-oxidized Ta/CoFeB/MgO/Ta (at 0 Pa) sample. These results suggest that surface oxidization in the Ta layer plays an important role in controlling the damping constant in the system.
Ta-O (1 nm)/CoFeB (1.3 nm)/MgO (1.3 nm)/Ta (1nm) stack films were fabricated on thermally oxidized Si substrates by the RF sputtering at room temperature. Ta-O layers were formed by naturally oxidizing thin Ta layers at the different Oxygen pressure (P_Oxygen) of 0.3, 0.1, and 0.03 Pa. The post-annealing process was conducted at 250 and 350oC in a vacuum.
Figure 1 shows the dependence of damping constant and the interfacial anisotropy K_s on P_Oxygen for as-deposited and annealed stack films. K_s was evaluated by the equation: K_s = (4pM_s, eff - 4pM_s)x(tCFBM_s/2) where the saturation magnetization was measured by VSM (M_s) and FMR measurements(M_s, eff), respectively; and tCFB is the thickness of CoFeB layer. For every film, both damping constant and K_s decrease as P_Oxygen increases, suggesting that these parameters correlated with each other [4]. On the other hand, the rate of the enhancement of the damping constant by annealing in every oxidized film (Ta-O/CoFeB/MgO/Ta) is lower than that in the non-oxidized Ta/CoFeB/MgO/Ta (at 0 Pa) sample. These results suggest that surface oxidization in the Ta layer plays an important role in controlling the damping constant in the system.