Magnetization reversal in Co-base nanowire arrays

The magnetic behaviour of ordered arrays of magnetic nanowires is controlled by the combined action of anisotropy energy terms determined by geometrical shape, crystalline structure and magnetostriction, as well as by the magnetostatic interactions among them. A number of works have been reported on the role of magnetostatic interaction in arrays of nanowires, sometimes focusing on nanowires with vanishing crystalline and magnetostrictive energy terms. Here, in turn we are interested in Co-base nanowires whose magnetocrystalline anisotropy plays a very important role. Arrays of Co-base nanowires offer novel, sometimes unexpected behaviour that is not fully understood. Such results are connected to their magnetocrystalline anisotropy, and to their complex magnetization reversal mode. Arrays of Co and Co-base nanowires have been fabricated by template-assisted method, by electroplating into highly ordered self-assembled pores of nanoporous alumina membranes. Their hcp or fcc crystal structure is confirmed to depend on length of nanowires as well as on the presence of selected elements in the composition. The magnetic behaviour of these arrays has been experimentally investigated as a function of (i) geometry (e. g. diameter and, particularly short length) and (ii) composition (e. g. adding Ni or Pd). A complementary study on its temperature dependence reveals the nature of the dominant anisotropy, while the angular dependence of hysteresis loops (e. g. coercivity and remanence) enables a deeper analysis of the magnetization reversal process. Micromagnetic reversal modes are reviewed and modelling and simulations procedures introduced. Complex rotational mechanisms are concluded to be responsible for the reversal process following micromagnetic modes distinct from those pure classically established. [GRAPHICS] . (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim