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), (10 (1) over bar0), (11 (2) over bar0) and (10 (1) over bar1) 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, K-eff (along longitudinal direction) of 1.42 x 10(6) erg/cc is observed in (0002) PO NWs, which changes sign (-1.50 x 10(6) erg/cc) in (10 (1) over bar0) PO NWs. The angular dependence of coercivity [H-C(theta)] in (0002) oriented Co NWs exhibits a non-monotonic behavior in both the 50 nm and 20 nm samples. The fitting of H-C(theta) 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 10(3) times higher NW areal-density than that in PCT membrane array. (C) 2013 Elsevier B.V. All rights reserved.