Comparing theoretical demagnetizing factors with the observed saturation process in rectangular shields

Abstract

An analytic expression is given for the ballistic demagnetizing factors, D′, of the general rectangular prism, in which the field is averaged over the middle cross section of the prism, and for the “side” demagnetizing factor, D″, in which the averaging is over the edges of the prism. The demagnetizing fields are compared with the applied field values when a 250×95×2.35 μm magnetic shield transfers into the saturated state. This shield was made of a Ni80 Fe20 film, with a small uniaxial magnetic anisotropy induced during the electroplating process. Domain structure and the process of magnetic saturation were imaged using wide-field Kerr microscopy in fields up to 400 Oe, both along the easy and the hard axes. The ballistic demagnetizing field is found to be close to the external field necessary to align magnetically the central part of the shield, while the full shield saturation takes place at a field above the recently published magnetometric demagnetizing field. Saturation fields along the hard uniaxial anisotropy axis are larger, due to effective anisotropy fields.