Structural and magnetic properties of nanocrystalline Ni78.5Fe21.5-x-yMoxCry synthesized by mechanical alloying

Abstract

Three different nanocrystalline intermetallic alloys of compositions Ni78.5Fe21.5, Ni78.5Fe16.5Mo5, Ni78.5Fe14Mo5Cr2.5 were synthesized by mechanical alloying. Appropriate amount of fine pure metal powders were mixed thoroughly and milled in a planetary ball mill in Argon (Ar) atmosphere. Various milling parameters were used for the alloying. The influence of milling parameters to the formation of alloy is discussed. The minimum time needed for the formation of the alloy with the milling parameters has been reported. The formation of alloy was observed by X-ray Diffraction (XRD) analysis. Various structural parameters were determined from these XRD patterns analyses. Lattice parameters were determined by Nelson-Riley function. Theoretical density of the powder samples were carried out by analyzing the XRD patterns. Average crystallite size and micro-strain was calculated using Williamson-Hall plot. The effect of low temperature annealing on the structural and magnetic properties were discussed. Rietveld refinement of the XRD patterns was carried out by TOPAS 3 software. Various structural parameters such as lattice parameters, density, crystallite size and strain were determined by these refinement analyses. Quantitative analysis of different phases was also done by Rietveld analysis. The variation of phases with milling time and annealing is reported. Structural parameters were also determined from the Neutron Diffraction (ND) analysis of the final alloyed powders. Rietan 2000 software was used to analyze the ND patterns. Surface morphology of the alloyed powders was determined by linear intercept technique using the Scanning Electron Microscopy (SEM) images and average particle sizes of the powders are reported. Homogeneity and the micro chemical composition of the different particles of the powders were investigated by Energy Dispersive X-ray (EDX) spectroscopy. The effect of heat treatment on the morphology and the chemical composition was discussed in some cases. DC magnetic properties of the samples were studied by Vibrating Sample Magnetometer (VSM). The effect of milling and annealing on the DC magnetic properties i.e., saturation magnetization, remanence magnetization and coercivity is reported. AC magnetic properties i.e. initial permeability for one composition was studied by Precession Impedance Analyzer and the variation of permeability with sintering time and temperature were discussed.