Magnetization reversal studies in structurally tailored cobalt nanowires

Cobalt nanowires (NWs) having hcp crystal structure are structurally tailored for different preferred orientations (PO) of (0002), (101¯0), (112¯0) and (101¯1) by varying bath temperature and bath concentration in commercially available 50 nm pore diameter polycarbonate (PCT) and 20 nm pore diameter anodic alumina (AAO) membranes. The magnetization studies show orientation dependent competition of magneto-crystalline anisotropy with shape anisotropy. The large effective anisotropy, Keff (along longitudinal direction) of 1.42×106 erg/cc is observed in (0002) PO NWs, which changes sign (−1.50×106 erg/cc) in (101¯0) PO NWs. The angular dependence of coercivity [HC(θ)] in (0002) oriented Co NWs exhibits a non-monotonic behavior in both the 50 nm and 20 nm samples. The fitting of HC(θ) data reveals that the magnetization reversal mechanism initially takes place by curling and subsequently changes to coherent rotation mode after a certain transition angle, which is higher in case of denser NW array. This increase in transition angle can be attributed to the increased magneto-static interactions in the AAO membrane array having 103 times higher NW areal-density than that in PCT membrane array.