Effect of geometry on magnetic domain structure in Ni wires with perpendicular anisotropy: A magnetic force microscopy study

We investigated the magnetic domain structure of thermally evaporated nickel wires with perpendicular anisotropy as a function of width and geometry. Magnetic force microscope images revealed the presence of stripe domains, which tended to orient themselves either perpendicular or parallel to the edges of the wires. This is in agreement with the result of the minimization of the total magnetic energy of a wire near an edge, which predicts the minima of energy in these two particular cases. The general orientation of the stripes in wider wires can be manipulated by using an in-plane external field, but the stripe orientation in the vicinity of the edge stays unaffected. A rough edge forces the stripe domains to orient themselves perpendicular to the edge, rather than parallel to it. In narrow wires, the stripe domains are parallel to the edge, and the width of the domain increases as the width of the sample is decreased in order to fit an integer number of domains in the wire.