Magnetization Reversal And Magnetic Anisotropy Of Fe Ni And Co Nanowires In Nanoporous Alumina Membranes

The magnetization reversal and magnetic anisotropy of Fe, Ni and Co nanowires is studied at low temperatures. All nanowires show a strong shape anisotropy with the easy axis being parallel to the long axis of the wires. Co nanowires additionally show a temperature dependent magnetocrystalline anisotropy along the hexagonal c-axis, which is directed nearly perpendicular to the long axis of the wires, as is confirmed by X-Ray diffraction measurements and reported by Strijkens et al. who performed NMR measurements on samples prepared in a similar way. Therefore, at low temperatures and for large wire diameters a competition between magnetocrystalline and shape anisotropies can be observed. Co wires with a small diameter, however, do not show a significant magnetocrystalline anisotropy. Fcc-Co, which is only known as a high-temperature Co modification and which does not have a large magnetocrystalline anisotropy constant, becomes the predominant Co modification here. Investigations on the size dependence of the switching field for Fe and Ni nanowires provide information about the magnetization reversal process, which takes place via a nucleation of small magnetic domains probably at the end of the wires, and subsequent propagation of the domain wall along the wire.