On the behavior of Ni Magnetic Nanowires as studied by FMR and the effect of “blocking”.

The development of nano-patterned membranes and nanowires (NW) is based on the interest in basic and applied research ranging from spintronics [Fert, 2008], chemical [Casanova et al., 2008], biosensing [Orosco et al., 2009; Pacholski et al., 2006], semiconductor [Yang, et al., 2010] and microwave applications [Darques et al., 2009] among others [Ferain & Legras, 2009]. In particular, the study and applications of NWs has grown extensively during the last decades. One possibility to fabricate NWs is based on electron beam lithography leading to well defined structures of no less than 100nm lateral size. In contrast with this technique there are other possibilities to generate nanoporous templates based on chemical or in physicochemical techniques [Pirota et al., 2010]. One of these uses energetic heavy-ion particle beams impinging on a polymer membrane and subsequent chemical etching [Fert & Piraux, 1999]. Such membranes are commercially available with varying diameters and pore-density. Also a two-step anodization process [Masuda & Fukuda, 1995; Nielsch et al., 2001] of aluminum leads to self-organized pores of amorphous anodized aluminum oxide (AAO) with a hexagonal order over relatively large regions (1-2m). The pores align perpendicular to the substrate and remain separated from each other. These AAO templates can be prepared using different solutions and conditions of anodization, leading to varying diameters (20nm -110 nm), separation (65 500nm), and degree of order [Niesch et al., 2001; Vazquez et al, 2004]. These templates were used for growing by electrodeposition the Ni NWs that are the subject of this chapter. Ferromagnetic NW can be approximated as uniformly magnetized single domains with reversal mechanisms that depend on the wire diameter [Hertel & Kirschner, 2004]. The magnetic characteristic of a NW array depends crucially on its effective anisotropy. The anisotropy measurement, its origin, and possible ways of modifying it, are of large interest in basic research and applications. For the characterization of magnetic NWs arrays ferromagnetic resonance (FMR) is an excellent technique as it yields direct information about the uniform precession mode