Cylindrical nanowire arrays: From advanced fabrication to static and microwave magnetic properties

Abstract

This article reviews information on arrays of cylindrical magnetic nanowires grown electrochemically inside ordered nanoporous alumina membranes, summarizing some of the most relevant aspects about the advanced synthesis of nanowires and their overall static and microwave magnetic properties. The electrochemical details for the preparation of templates with well-defined hexagonal ordering are addressed focusing on the different anodization methods including mild, hard, pulsed or anodization of aluminum rods. A section follows on the growth of metallic nanowires, either as single element (i.e., Fe, Ni, Co), alloys (i.e., CoFe, CoNi, FeNi) or modulated in composition (i.e., Ferromagnetic/Metal). The static magnetic properties as anisotropy, coercivity and magnetostatic interactions are overviewed with particular emphasis on the influence of magnetocrystalline anisotropy and on the temperature dependence of those properties. The last section is devoted to the ferromagnetic resonance of nanowire arrays of different composition. The dependence of microwave absorption on the orientation of applied field is also a useful tool to determine the magnetic anisotropy parameters and the significance of magnetostatic interactions. The magnetization easy axis can be switched from the nanowire direction to the plane of the membrane as the nanowire filling factor increases or at a compensation temperature, in both cases it derives from the energetic balance of anisotropy and magnetostatic interactions among nanowires. A final subsection is devoted to the spin waves resonance spectra, and the perspectives of applications making use of microwave properties. We expect the article can be useful for researchers interested on the topic and provide a wide overview on the matter to those starting a new research line.