The microstructure of a CoNiFeB film for a soft magnetic underlayer of perpendicular recording media, which was deposited by electroless plating on a Si wafer, has been investigated by transmission electron microscopy and a three-dimensional atom probe. After the deposition of the CoNiFeB film on a Ni underlayer, Hc decreased from about 62 to about 3 Oe. Based on the microstructure observation results, the decrease of Hc was concluded to be the result of reduced magneto-elastic energy. The good adhesiveness between the soft underlayer (SUL) and the Si substrate was found to be due to the composition gradient.
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