Field-induced domain wall motion of amorphous [CoSiB/Pt]N multilayers with perpendicular anisotropy

Amorphous CoSiB/Pt multilayer is a perpendicular magnetic anisotropy material to achieve high squareness, low coercivity, strong anisotropy, and smooth domain wall (DW) motion, because of the smoother interface compared with crystalline multilayers. For [CoSiB(6 Å)/Pt (14 Å)]N multilayers with N = 3, 6, and 9, we studied the field-induced DW dynamics. The effective anisotropy constant K1eff is 1.5 × 106 erg/cm3 for all the N values, and the linear increment of coercive field Hc with N gives constant exchange coupling J. By analyzing the field dependence of DW images at room temperature, a clear creep motion with the exponent μ = 1/4 could be observed. Even though the pinning field Hdep slightly increases with N, the pinning potential energy Uc is constant (=35 kBT) for all the N values. These results imply that the amorphous [CoSiB/Pt]N multilayers are inherently homogeneous compared to crystalline multilayers. For N ≤ 6, the pinning site density ρpin is less than 1000/μm2, which is about 1 pinning site per the typical device junction size of 30 × 30 nm2. Also, the exchange stiffness constant Aex is obtained to be 0.48 × 10−6 erg/cm, and the domain wall width is expected to be smaller than 5.5 nm. These results may be applicable for spin-transfer-torque magnetic random access memory and DW logic device applications.