Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures

TL;DR

This study investigates how pH and annealing temperature affect the low-temperature magnetic properties, spin freezing, and magnetic field responses of Ni1.5Fe1.5O4 ferrite, revealing complex magnetic behaviors including superparamagnetism and spin glass characteristics.

Contribution

It provides new insights into the influence of synthesis conditions on the magnetic behavior and spin dynamics of Ni1.5Fe1.5O4 ferrite, highlighting the roles of particle size, surface spins, and disorder.

Findings

Sample at pH 12 and 800°C shows a sharp magnetization peak at 105 K.

Magnetization peaks are incomplete up to 350 K in other samples.

AC susceptibility indicates cluster spin glass behavior depending on pH and annealing temperature.

Abstract

We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as the function of pH at which the material was prepared by chemical route and post annealing temperature. The material is a ferri or ferromagnet, but showed magnetic blocking and random spin freezing process on lowering the measurement temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C showed a sharp magnetization peak at 105 K, the superparamagnetic blocking temperature of the particles. The magnetization peak remained incomplete within measurement temperature up to 350 K for rest of the samples, although peak temperature was brought down by increasing applied dc field. The fitting of temperature dependence of coercivity data according to Kneller law suggested random orientation of ferromagnetic particles. The fitting of saturation magnetization according to Bloch law provided the exponent that largely deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt increase of saturation magnetization below 50 K suggested the active role of frozen surface spins in low temperature magnetic properties. AC susceptibility data elucidated the low temperature spin freezing dynamics and exhibited the characters of cluster spin glass in the samples depending on pH value and annealing temperature.