Magnetic microstructure and noise property of electrolessly deposited CoNiFeB SoftMagnetic underlayer

A CoNiFeB soft magnetic underlayer (SUL) was prepared by electroless deposition using dimethylamineborane as the reducing agent. A 2.5-inch NiP/Al disk was used as the substrate, on which a NiP nonmagnetic amorphous-layer was also electrolessly deposited. The coercivity H_c of as-deposited CoNiFeB films in the direction parallel to the surface exhibited a convex-parabolic dependency on the film thickness. The in-plane M-H loops and the two-dimensional Kerr effect images of the CoNiFeB film showed a nearly isotropic character with H_c of 25 Oe and no marked domain boundaries. From magnetic force microscope measurements, we confirmed that these behaviors resulted from the formation of striped magnetic domains caused by slightly perpendicular magnetic anisotropy of SUL. As far as the noise characteristics are concerned, dc noise was increased with H_c, while spike noise was suppressed.