Angular dependence and proximity effect of dense arrays of cobalt nanowires as rare-earth-free permanent magnets

Abstract

Ferromagnetic Co nanowires based on the synergistic effect of shape anisotropy and magnetocrystalline anisotropy appear to be apt candidates as rare-earth-free permanent magnetic materials. This study systematically investigates the angular dependence and proximity effects on the magnetic properties of polyol-synthesized Co nanowires using first-order reversal curve (FORC) analysis. The FORC diagram of the dilute Co nanowire array exhibits characteristics similar to an ensemble of non-interacting single-domain particles. Angular-dependent FORC analysis, performed on the dilute nanowire array with easy-axis angles ranging from 0° to 90° relative to the applied field, reveals a strong correlation between the irreversible magnetization fraction and the magnetic properties. The proximity effect arising from nanowire stacking enhances magnetostatic interactions, resulting in FORC pattern expansion. Specifically, the FORC diagram of the high-density Co nanowire array exhibits a distinctive “wishbone” or boomerang structure. The physical significance of the FORC diagrams for the Co nanowire array was discussed based on the Stoner–Wohlfarth model. This work offers valuable guidance for designing and controlling the nanomagnetic characteristics of Co nanowires, with potential implications for advancing their application in permanent magnets.