Magnetic hardening and exchange bias effect in dual-phase Co₃Mn nanowire arrays

Mn-based magnetic alloys and compounds having large magnetic anisotropy are currently focused as alternate materials for various spintronic applications. In this work, magnetization behavior of Co₃Mn alloy nanowires (NWs) was investigated by fabricating with well-known template-based electrodeposition method where the electrodeposition was carried out at sinusoidal high voltage. The NWs were annealed at 300 °C and 400 °C with 10 °C/min heating and cooling rate to eliminate the crystal defects caused by high-voltage deposition. Crystal structure analysis displayed the as-deposited NWs were crystallized into a face-centered cubic (fcc) structure with crystallite size 24.93 nm, while the hexagonal close pack (hcp) phase with crystallite size 38.61 nm was induced after annealing. The as-deposited NWs exhibited the soft ferromagnetic behavior with coercivity (H_C) = 128 Oe and saturation magnetization (M_S) = 311 emu/cm³ along axial direction but magnetic hardening induced after annealing with H_C = 688 Oe and M_S = 228 emu/cm³ caused by strong pinning effects and elastic coupling between hcp and fcc phase. Interestingly, the asymmetric shift in MH-loops of annealed NWs was noted below 150 K when the temperature-dependent MH-loops measured after cooling the sample in the magnetic field. This observation confirmed the existence of exchange bias effect in NWs caused by short-range exchange interaction between ferromagnetic fcc phase and antiferromagnetic hcp phase.