Magnetic Characterization of Electrodeposited Nanocrystalline Ni and Ni-Fe alloys

Abstract

<p>This research study has been devoted to the study of magnetic properties and magnetic transport of nanocrystalline Ni and Ni-15% Fe alloys consisting of randomly oriented grains with an average size of 23 and 12 (nm), respectively. The structures of the deposits were confirmed by the XRD analysis using Rietveld refinement technique. The as-deposited Ni and Ni-15%Fe sample was comprised exclusively of the γ phase with lattice parameter of 3.5270 (nm) and 3.5424 (nm), respectively. The small increase in lattice parameter was attributed to the replacement of iron solutes in the Ni sites in lattice. Texture analysis of nanocrystalline Ni and Ni-15%Fe revealed that textures components of both materials is qualitatively the same and vary in terms of volume fraction. Both material showed strong <100> fibre texture with some contribution of the <111> component. The calculated volume fraction of the <100> and <111> components were respectively 17.157% and 3.201% for Ni and, 22.032% and 6.160% for Ni-15%Fe and the rest being confined to the random texture.</p> <p>Magnetic measurements show that all samples exhibit low loss hysteresis loops with high permeabilities. The presence of 15%Fe in Ni leads to enhancement of the saturation magnetization (M_s) regardless of the direction of the applied field. M_s shows an increase from 60.169 (emu/gr) in nanocrystalline Ni to 93.67 (emu/gr) in Ni-15%Fe sample at T=2K. No strong temperature–dependence of the magnetization was observed for samples, but the magnetization of the Ni-15%Fe samples at T=2K were slightly higher than that of T=298K. The coercivity values of nanocrystalline Ni-15%Fe were in all cases smaller than that of nanocrystalline Ni samples. Good agreement between random anisotropy model (RAM) theory and experiment for nanocrystalline Ni and Ni-15%Fe samples was observed. The ferromagnetic exchange length (L_ex) was larger than the average grain size (D) for samples at all times. The effective magnetic anisotropy constants (K_eff) of the nanocrystalline Ni and Ni-15%Fe alloys were measured using the law of approach to saturation. At T=2K, the K_eff of Ni-15%Fe samples were measured to be 1.7037´10⁵ (erg/cm³) and 2.71996 ´10⁵ (erg/cm³) at field parallel and perpendicular, respectively. These values were almost half of the values obtained for nanocrystalline Ni samples 4.66091´10⁵ (erg/cm³) and 4.19703´10⁵ (erg/cm³). Temperature dependence measurements showed that K_eff constants decrease with increasing temperature. The angular dependence MR studies on nanocrystalline Ni and Ni-15%Fe resulted in a twofold, and a fourfold symmetric behaviour, respectively. The field dependence MR measured at various sample tilt with respect to the applied field, showed various trends from pure positive MR to pure negative MR, which partially could be explained by magnetocrystalline anisotropy of the samples.</p>