Irreversible evolution of angular-dependent coercivity in Fe80Ni20 nanowire arrays: Detection of a single vortex state

The irreversible evolution of magnetic coercivity in arrays of 75 nm diameter Fe 80 Ni 20 nanowires (NWs) has been explored by means of first-order reversal curve (FORC) analysis as a function of the angle between the magnetic field and the NW axis (0°≤ θ ≤90°). The Fe 80 Ni 20 NWs with lengths up to 60 μm were fabricated using a pulsed electrodeposition method into hard-anodic aluminum oxide templates with an interpore distance of 275 nm. Investigating the interwire and intrawire magnetostatic interactions, the angular FORC (AFORC) diagrams indicated enhanced intrawire interactions with increasing length and θ ( θ =83° for 60 μm long NWs. At θ =90°, the NWs reversed magnetization through transverse domain wall, involving a reversible component by a fraction of 95%. Furthermore, the transition angle between the reversal modes was found to decrease with increasing aspect ratio from 200 to 800. The irreversible angular-dependent coercivity ( H c Irrev ( θ )) of Fe 80 Ni 20 NWs was extracted from the AFORC measurements and compared with the major angular dependence of coercivity ( H c Major ( θ )) obtained from the conventional hysteresis loop measurements. While H c Major ( θ ) showed a non-monotonic behavior, H c Irrev ( θ ) constantly increased with increasing θ ( H c Irrev ( θ ) for irreversible switching of VDW when 0°≤ θ ≤86°.