Effective anisotropy in Fe-Ni nanowire arrays with strong dipolar interaction

The effective magnetic anisotropy field Heff of Fex Ni(100-x) (x = 15, 25, 38) nanowires of 65 nm diameter forming ordered arrays within dense alumina templates of-35% porosity, was determined. Different values for Heff were obtained depending on the determination method, which were: magnetization evolution along major hysteresis loops; ferromagnetic resonance at 34 GHz; and magnetization switching by curling nucleation (through angular variation of the coercive field). Heff values determined from magnetization measurements differ from those arising from FMR measurements, being these latter quite smaller in every case. No evidence of an easy plane behavior was found, as theoretically predicted for high porosity arrays as ours. These results suggest that new internal degrees of freedom need to be considered for the effective anisotropy description in quasistatic hysteresis loops, during polarization reversal and in ferromagnetic resonance dynamic processes, to understand and model these experimental findings. We discuss possible causes.

Automated summary

The effective magnetic anisotropy field Heff of Fex Ni(100-x) (x = 15, 25, 38) nanowires within dense alumina templates of-35% porosity was determined using different methods including magnetization evolution, ferromagnetic resonance, and magnetization switching. The results showed variations in Heff values depending on the determination method, with the values from magnetization measurements being quite smaller than those from FMR measurements. It was suggested that new internal degrees of freedom need to be considered to describe the effective anisotropy in different processes.