Micromagnetics of Ni-nanowires filled in nanochannels of porous silicon

An array of ferromagnetic nanowires embedded in silicon is fabricated using an anodizing and electroplating process. During the former one oriented porous silicon channels are fabricated whereas by the latter process Ni is incorporated into these channels. The electrodeposited Ni-wires have a great pore-length to pore-diameter (aspect) ratio up to 1000 : 1 (typical diameters between 10 and 60 nm, pore-length from 10 to 30 μm). Due to this property the samples exhibit a magnetic perpendicular anisotropy. The micromagnetic properties of Ni (e.g. Bloch-wall thickness) are responsible for the peculiar magnetic behaviour of this ferromagnet/silicon nanocomposite. Structural as well as magnetic investigations like scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and SQUID-magnetometry display this nanocomposite as a bimodal ferromagnetic structure consisting of perpendicularly oriented Ni-wires and of single domain Ni-granules embedded in the silicon based matrix. The hysteresis curve outlines a two-fold magnetic switching, one at low fields (∼0.05 T) and the second at high fields (> 3 T). The micromagnetic magnetization reversal is treated in terms of an analytic formulation.