Crystalline analysis of permalloy narrow wires subject to current pulses

We investigate crystalline structures of a permalloy nanowire subject to current pulses by using standard transmission and scanning electron microscope techniques, together with the analysis of magnetic states by means of Lorenz microscopy. We find that crystalline grains grow slightly larger in a current region around the Curie temperature, which does not affect significantly the uniformly-magnetized state in the wire because of strong uniaxial shape anisotropy given by the wire geometry. When crystalline grains grow large enough to additionally provide in-plane anisotropy comparable to the shape anisotropy by averaging crystalline anisotropy over the grains, the magnetic ripple will be induced in the wire. Such situations can be found in the case when very large current pulses are applied to the wire.