Variation of magnetic anisotropy and temperature-dependent FORC probing of compositionally tuned Co-Ni alloy nanowires

The magnetic microstructure of Co-Ni binary alloy nanowires electrodeposited with controlled composition into nanoporous aluminum oxide templates can be represented as an ensemble of stochastic magnetic domains, whose size is determined by the magnetic correlation length. Using a method based on the approaching of magnetization to saturation, we defined the dimension of regions with magnetic orientation coherency as the stochastic domain size. Based on the experimental measurements of magnetization curves near saturation and first order reversal curves (FORC), we described a relationship between the macroscopic and microscopic parameters of the nanowires depending on the crystal structure observed by high-resolution transmission electron microscopy in terms of the random anisotropy model. The alloy composition strongly determines the crystal structure, in particular, the grain size and hcp/fcc phase distribution, and influences the effective magnetic anisotropy energy providing the direction of easy magnetization in the nanowire arrays. The characterization of Co-Ni arrays by FORC method at room and low temperatures revealed the transformation of magnetic behavior and certain contributions to the energy of the effective magnetic anisotropy.