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

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 demagneti zing fields are compared with the applied field values when a 250x95x2.35 m u m magnetic shield transfers into the saturated state. This shield was mad e of a Ni-80 Fe-20 film, with a small uniaxial magnetic anisotropy induced during the electroplating process. Domain structure and the process of magn etic saturation were imaged using wide-field Kerr microscopy in fields up t o 400 Oe, both along the easy and the hard axes. The ballistic demagnetizin g field is found to be close to the external field necessary to align magne tically the central part of the shield, while the full shield saturation ta kes place at a field above the recently published magnetometric demagnetizi ng field. Saturation fields along the hard uniaxial anisotropy axis are lar ger, due to effective anisotropy fields. (C) 2000 American Institute of Phy sics. [S0021-8979(00)20108-4].