Enhancement of microstructure and initial permeability due to Cu substitution in Ni 0.50− xCu xZn 0.50Fe 2O 4 ferrites

Abstract

Structural and magnetic properties of Cu substituted Ni 0.50− x Cu x Zn 0.50Fe 2O 4 ferrites (where x=0.0–0.25) prepared by an auto combustion method have been investigated. The X-ray diffraction patterns of these compositions confirmed the formation of the single phase spinel structure. The lattice parameter increases with the increase in Cu 2+ content obeying Vegard's law. The particle size of the starting powder compositions varied from 22 to 72 nm. The theoretical density increases with increase in copper content whereas the Néel temperature decreases. The bulk density, grain size and permeability increases up to a certain level of Cu 2+ substitution, beyond that all these properties decrease with increase in Cu 2+ content. The bulk density increases with increase in sintering temperatures up to 1250 °C for the parent composition, while for substituted compositions it increases up to 1200 °C. Due to substitution of Cu 2+, the real part of the initial permeability increases from 97 to ∼390 for the sample sintered at 1100 °C and from 450 to 920 for the sample sintered at 1300 °C. The ferrites with higher initial permeability have a relatively lower resonance frequency, which obey Snoek's law. The initial permeability strongly depends on average grain size and intragranular porosity. The saturation magnetization, M s, and the number of Bohr magneton, n( μ B) , decreases up to x=0.15 due to the reduction of the A–B interaction in the AB 2O 4 spinel type ferrites. Beyond that value of x, the M s and the n( μ B) values are enhanced. The substitution of Cu 2+ influences the magnetic parameters due to modification of the cation distribution.