Variable-size Ni magnetic nanowires as observed by magnetization and ferromagnetic resonance

Abstract

We present magnetization and ferromagnetic resonance (FMR) measurements on arrays of Ni nanowires grown by electrodeposition on self-organized nanoporous alumina templates. The study focuses on the measurement by FMR of the anisotropy of these systems and its correlation with the magnetization loops as the wire diameter ( d) is changed in a series of three samples. The magnetization data indicates an easy axis along the wire for the d=35 and 55 nm, changing into an easy plane for d=65 nm (all samples have an average inter-wire separation D∼110 nm). FMR resonance allows observing the anisotropy effects in detail and is consistent with magnetization measurements. Yet FMR shows a complex behavior in the large- d sample that can be interpreted as resulting from a prevailing easy-plane anisotropy with some portions of the sample with easy axis along the wires, thus unveiling an inhomogeneous character.