Magnetic hysteresis of Ni nanowires

Magnetization processes in Ni nanowire arrays are investigated. The wires a re produced by electrodepositing Ni into porous anodic alumina and exhibit coercivities of the order of 0.05 T (500 Oe) along the wire axis. Transmiss ion-electron microscopy of freed wires shows that the wires are polycrystal line and resemble a chain of nanocrystallites. To model the hysteresis loop s, the wires are treated as one-dimensional random-anisotropy magnets where the magnetocrystalline bulk anisotropy is a weak perturbation to the leadi ng anisotropy contribution. The calculation yields an analytical equation f or the magnetization as a function of the applied magnetic field. For small and moderate reversed fields, the agreement between theory and experiment is very good, but the applicability of the model breaks down close to the c oercive field. This failure is explained by the neglect of higher-order per turbation terms describing, for example, magnetic localization effects.