Effect of crystallographic texture on magnetic characteristics of cobalt nanowires

Abstract

Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition in etched ion-track polycarbonate membranes. Structural characterization of these nanowires with diameter 70, 90, 120 nm and length 30 μm was performed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. The as-prepared wires show uniform diameter along the whole length and X-ray diffraction analysis reveals that [002] texture of these wires become more pronounced as diameter is reduced. Magnetic characterization of the nanowires shows a clear difference of squareness and coercivity between parallel and perpendicular orientations of the wires with respect to the applied field direction. In case of parallel applied field, the coercivity has been found to be decreasing with increasing diameter of the wires while in perpendicular case; the coercivity observes lower values for larger diameter. The results are explained by taking into account the magnetocrystalline and shape anisotropies with respect to the applied field and domain transformation mechanism when single domain limit is surpassed.

Keywords: Co nanowires; Electrodeposition; Magnetic properties.

Figure 1

Experimentally measured deposition current as a function of deposition time recorded during wires synthesis. Zone-I, II, and III are explained in the text

Figure 2

a, b SEM micrographs of 120- and 90-nm-diameter cobalt wires, respectively, c EDS spectrum of cobalt nanowires. In the pattern, the Cu and Au peaks represent the substrate materials, d TEM micrograph of a 70-nm-diameter wire and respective SAED pattern (inset)

Figure 3

XRD diffractogram of cobalt nanowires

Figure 4

Comparison of hysteresis loops of cobalt nanowires. a, c, e The loops taken when the magnetic field was applied parallel to the wire long axis, b, d, f The loops taken when the field was applied perpendicular to the wire long axis. g, h Coercivity values as a function of diameter (calculated from hysteresis loops) for applied filed parallel and perpendicular to the wire long axis, respectively

Figure 5

Schematic diagram showing directions of shape and magnetocrystalline anisotropies and wire long axis for [100], [101], and [002] textures