Angular dependence of the coercivity and remanence of ferromagnetic nanowire arrays

TLDR

The coercivity and remanence variations in ferromagnetic nanowire arrays arise from distinct magnetization reversal mechanisms in small wires. The study measured hysteresis loops of nanowire arrays fabricated by pulsed electrodeposition in anodic alumina and polycarbonate membranes, varying wire material, length, and field orientation to determine coercivity, remanence, and the influence of interwire magnetostatic interactions. In PCTE membranes, coercivity versus angle curves show bell‑shaped behavior for CoNiFe, NiFe, and Co wires, while Ni wires shift to a different shape as diameter shrinks to 30 nm; interwire magnetostatic coupling lowers coercivity and remanence, can rotate the easy axis, and alters reversal mechanisms, though the coupling is weaker than predicted by independent precession theory.

Abstract

Magnetization properties of magnetic nanowire arrays are studied on various ferromagnetic materials grown in anodic alumina (alumite) and track etched polycarbonate (PCTE) membranes by pulsed electrodeposition. Magnetization curves were measured as functions of wire material, field orientation, and wire length. The coercivity (Hc) and remanent squareness (S) of the various wire arrays were derived from hysteresis loops as a function of angle (θ) between the field and wire axis. For PCTE membranes, Hc(θ) curves for CoNiFe, NiFe, and Co nanowire arrays all show an otherwise-bell-type variation, while they change shapes from the otherwise bell to bell type for Ni nanowire arrays as the wire diameter decreases to 30 nm. These characteristics can be understood based on different magnetization reversal mechanisms of small wires. The effect of magnetostatic interaction among wires on the magnetic properties was examined by changing the wire lengths in alumite membranes. It is found that the interaction reduces Hc and S values significantly and may cause the overall easy axis change from parallel to perpendicular to the wire axis. However, the interaction is much weaker than expected from an independent precession theory. The strong coupling among the wire may also induce a change of magnetization reversal mechanism.