Structural and Magnetic Properties of Single Domain PEG-Coated FexNi80−xCo20 (x = 20, 40) Ternary Alloys Synthesized by Chemical Method

Abstract

In the present study, we have synthesized nanocrystalline FexNi80−xCo20 (x = 20 and 40) alloys via modified sodium borohydride reduction route in aqueous medium. The phase purity and microstructural analysis of the materials were done using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fe–Ni–Co alloys crystallize in face centered cubic (fcc) structure having the values of lattice parameters, a = 3.5460 and 3.5634 A, for Fe20Ni60Co20 and Fe40Ni40Co20, respectively. The average crystallite sizes were found to be 30 and 26 nm for Fe20Ni60Co20 and Fe40Ni40Co20, respectively. Fe20Ni60Co20 and Fe40Ni40Co20 alloys crystallize in nearly spherical shape morphologies having TEM particle sizes of 24 and 36 nm, respectively. Selected area electron diffraction (SAED) patterns confirm face centered cubic crystal structure and polycrystalline nature of the materials. Low temperature studies indicate that Fe–Ni–Co alloys show ferromagnetism at least up to 300 K. The effective magnetic anisotropy constant (K) for Fe20Ni60Co20 and Fe40Ni40Co20 alloys are found to be 14 and 4.2 kJm−3, respectively. These results have been explained on the basis of size, shape and surface effects in the nano-materials. The contribution corresponding to spin relaxation and dipolar interactions between nano-particles on magnetic characteristics of Fe20Ni60Co20 and Fe40Ni40Co20 alloys have been explained qualitatively during the magnetic analysis.