Surface, interface and bulk studies of NiFe nanometer films for magnetoresistive heads

Polycrystalline Ni81Fe19 films have been vapor-deposited in a forming field onto a 100-μm-thick borosilicate glass. The free surface and film/substrate interface magnetization has been probed using magneto-optical Kerr effect (MOKE) magnetometry, and bulk measurements have been taken using an alternating gradient force magnetometer. Saturation magnetostriction constants were derived from the strain dependence of the anisotropy field in the MOKE measurements, separating out for the first time free surface and interface effects. The free surface showed a clear uniaxial anisotropy with a low dispersion, while the interface showed a mixture of domain switching and moment rotation. We interpret the data in terms of a gradient in magnetic properties through the sample, and discuss consequences for magnetoresistive heads.