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▲ [11p-Z08-3] Study on the dynamic magnetic properties in Ta-O/Co-Fe-B stacks with different interface condition
Keywords:Temperature dependence of Magnetization dynamics, surface oxidized TaOx/CoFeB, Broadband ferromagnetic resonance measurement
Ta-O (1 nm)/Co-Fe-B (1.3 nm)/MgO (1.3 nm)/Ta (1 nm) stacks were fabricated the RF sputtering. Ta-O layers were formed by naturally oxidizing thin Ta layers at the different oxygen pressure (P). The post-annealing process was conducted at a temperature (T_an) ranging from 523 K to 673 K in a vacuum to control the interfacial anisotropy (K_s). As for their dynamic magnetic properties, the effective saturation magnetization (4pi_M_s, eff) and the damping constant (a) were estimated using a broadband FMR measurement.
Figure 1 shows the change in 4pi_M_s, eff and (a) with T_an for the stacks oxidized at different P. For all stacks, as T_an increases, 4pi_M_s, eff slightly decreases while (a) increases. At all T_an except 673 K, (a) values at P above 0.1 Pa are lower than that at P of 0.03 Pa. Furthermore, to get more insight, K_s was estimated by K_s = (4pi_M_s, eff - 4pi_M_s)x(t_Co-Fe-B x 4pi_M_s/2), where t_Co-Fe-B is the Co-Fe-B layer thickness, and 4pi_M_s is the saturation magnetization, and then was summarized in Fig. 1 (c) as a function of T_an. The values at P above 0.1 Pa become lower than that at P = 0.03 Pa, meaning that (a) and K_s are correlated with each other in the surface oxidized stacks. These results suggested that the surface oxidization plays an important role in controlling (a) in these stacks.<br