Ion irradiation induced effects and magnetization reversal mechanism in (Ni₈₀Fe₂₀)_1-xCo_x nanowires and nanotubes

The effect of Co on the ferromagnetic characteristics of the Ni₈₀Fe₂₀ nanocylinders having zero magnetostriction and soft magnetic nature is an interesting field of research. The (Ni₈₀Fe₂₀)_1-xCo_x nanocylinders have been prepared by electrodeposition into commercially available anodized aluminum oxide (AAO) nanoporous templates. The analysis of magnetization reversal from the angular dependence of coercivity has been studied in detail. This angular dependence of coercivity has shown a transition from curling to nucleation mode as a function of field angle for all (Ni₈₀Fe₂₀)_1-xCo_x nanocylinders depending upon the critical angle. The shape anisotropy, dipole-dipole interactions, surface effects and magnetocrystalline anisotropy have been found to play an effective role for the spontaneous magnetization in nanowires and nanotubes. It has been interestingly observed that the magnetostatic interactions or dipole-dipole interactions are dominant in nanocylinders regardless of its geometry. Furthermore, the prepared samples have been irradiated with He²⁺ ions (energy E=2 MeV, fluence=10¹⁴ ions/cm² and ion current=16 nA) at room temperature using a 5-UDH-2pelletron tandem accelerator. The irradiations have created defects and these defects have induced changes in magnetization as a result an increase in coercivity as function of the ion fluences is observed. Such kind of behavior in coercivity enhancement and magnetization reduction can also be attributed to the stress relaxation and percolation in nonuniform states of ferromagnetic alloys, respectively.