Characteristic length of domain structures and its effect on the coercive force of ferromagnetic materials

摘要

The magnetic properties of micrometer‐size Permalloy thin films have been investigated for a variety of sample thicknesses, aspect ratios, and sizes. The formation of edge domains was an important factor in the magnetization response of the sample to an applied external magnetic field. Sample coercivity depended on the length of the domain wall structure. Small specimens (6.5 μm wide) have high coercivity, whereas large samples (104 μm wide) approach the bulk‐film value. The reduced length, defined as the ratio of the edge‐domain extent (or characteristic length) to the sample length, and its dependence on sample size, aspect ratio, and thickness were studied. Samples with low aspect ratio have wall structures throughout the specimen, giving rise to higher coercivities and correspondingly larger reduced lengths. Samples with large aspect ratio have wall structures confined to the edge areas, lower coercivities, and shorter reduced lengths. The absolute domain size increased as the sample increased, and reduced length approached a constant value for all samples with a given aspect ratio. The reduced length was approximately proportional to the reciprocal of the aspect ratio.