Lorentz Microscopy in Polycrystalline Ni–Fe Films 2000-Å Thick

Abstract

The use of Lorentz microscopy has been reported on polycrystalline films 1450 Å and thinner. In this paper the use of Lorentz microscopy on polycrystalline films in the thickness range between 1200 and 2000 Å is presented, and some of the more unexpected results discussed. The intermediate wall cross‐ties observed in a 1450‐Å film as reported earlier were not found in a low‐dispersion Ni–Fe film 2000±50 Å thick (the thickness measurements were made carefully with torque magnetometer, Tolansky apparatus, and loop checker with calibrated standard), but when the film was annealed in vacua so that the crystallites became enlarged and H_c and α₉₀ increased, the intermediate wall cross‐ties were observed. The conclusion is that the biaxial inhomogenities caused the 180° Bloch wall to become a 170° wall in some segments and a 190° wall in others. Then, according to intermediate wall theory, these non‐180° walls must have a Néel component which alternates along the length of the wall, thereby causing the cross‐ties. Stripe domains were also observed in samples from other evaporations, but when fields were applied in the microscope to observe the switching processes, the stripes were erased and could not be brought back.