Static Magnetization Reversal in Thin Films of Co–Ni–P

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Abstract
Electrodeposited films of Co–Ni–P containing 14% nickel and 1% phosphorus by weight and having thickness 0.05 to 0.2 μ showed the following magnetic properties—high coercivity (300–550 Oe), high ratio of remanent‐to‐saturation moment (∼0.90), steep‐sided hysteresis loops and isotropy in the film plane. The process of magnetization reversal was studied by using a sensitive Hall probe to measure and map the horizontal component of the flux above the surface of the film after increasing reverse fields has been applied. This technique was used since neither the Bitter pattern method nor the Kerr effect revealed the natural pattern of magnetization reversal. However, it was possible to introduce, deliberately, a small region of reversed magnetization by means of the field from a magnetic recording head and examine this region by all three methods. This provided a method of checking the interpretations of the Hall effect data. It was found that these films employ a unique mode of magnetization reversal. Initially, small regions of reversed magnetization are established throughout the film, and these regions grow together to form elongated switched areas whose long dimensions are always perpendicular to the direction of applied field. The reversal pattern is highly reproducible in a given sample for a given field direction and reverses when the field direction reverses. This switching behavior is dependent on the direction of the field with respect to the sample, the long direction of the reversed regions always being perpendicular to the applied field. The sign of the vertical component of the flux from the sample was compared above and below the sample to determine whether magnetization perpendicular to the film plane existed. No such regions were found with a Hall probe of sensitive area down to 25×25 μ.

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