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

초록

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 angstrom)/Pt (14 angstrom)](N) multilayers with N = 3, 6, and 9, we studied the field-induced DW dynamics. The effective anisotropy constant K-1(eff) is 1.5 x 10(6) erg/cm(3) for all the N values, and the linear increment of coercive field H-c 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 mu = 1/4 could be observed. Even though the pinning field H-dep slightly increases with N, the pinning potential energy U-c is constant (=35 k(B)T) 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 rho(pin) is less than 1000/mu m(2), which is about 1 pinning site per the typical device junction size of 30 x 30 nm(2). Also, the exchange stiffness constant A(ex) is obtained to be 0.48 x 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. (C) 2014 AIP Publishing LLC.

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