Coercivity mechanism and microstructure of (Co/Pt) multilayers

The coercivity mechanism of (Co/Pt) multilayers with high H _c and high squareness fabricated by sputtering is mainly due to the wall pinning rather than the nucleation process. In order to estimate the size of a wall-pinning site, a study of the temperature dependence of the coercivity, perpendicular magnetic anisotropy, and saturation magnetization for multilayers fabricated under various substrate conditions has been carried out. The size r₀ of the pinning sites of about 4 Å was obtained for the multilayer film deposited onto an etched SiN_x film. The size r₀ increases with less interface-sharpness, which was confirmed by X-ray low angle diffraction. This implies that the pinning site is closely related to the interfacial region. An inhomogeneity near the interface between Co and Pt is believed to play a major role as pinning for a wall motion. This result is compared to the case of Tb₂₆(FeCo)₇₄ films, where the size is found to be about 60 Å ~250 Å