Structure and magnetic properties of ferromagnetic nanowires in self-assembled arrays

TLDR

The study investigates the static and dynamic aspects of magnetization reversal in nanowire arrays. The arrays were fabricated by electrodeposition of Fe, Co, and Ni into porous anodic alumina templates with diameters down to 5 nm, and their magnetic properties were examined across temperatures. The nanowires exhibit bcc Fe, fcc Ni, and mixed fcc/hcp Co structures with nanometer‑scale grains; coercivity follows a 3/2‑power thermal activation law, varies with diameter, and transitions from quasicoherent nucleation to curling‑like nucleation, with a model providing explicit expressions for coercivity, localization length, and activation volume.

Abstract

Static and dynamic aspects of the magnetization reversal in nanowire arrays are investigated. The arrays have been produced by electrodeposition of ferromagnetic metals (Fe, Co, and Ni) into porous anodic alumina templates, with diameters as small as 5 nm. The crystal structures of the nanowires are bcc (Fe) and fcc (Ni) and a mixture of fcc and hcp (Co), with grain sizes of a few nanometers. Magnetic properties as a function of temperature are investigated. The temperature dependence of coercivity can be understood in terms of thermal activation over an energy barrier with a $\frac{3}{2}$-power dependence on the field. Coercivity as a function of diameter reveals a change of the magnetization reversal mechanism from localized quasicoherent nucleation for small diameters to a localized curlinglike nucleation as the diameter exceeds a critical value determined by the exchange length. The quasicoherent limit is described by a model that yields explicitly real-structure-dependent expressions for coercivity, localization length, and activation volume.