Probing low temperature non-equilibrium magnetic state in Co$_{2.75}$Fe$_{0.25}$O$_{4+\delta}$ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments

TL;DR

This study investigates the low-temperature magnetic states of Co$_{2.75}$Fe$_{0.25}$O$_4$ spinel oxide using various experimental techniques, revealing a non-equilibrium magnetic structure with phase sensitivity to magnetic fields.

Contribution

It provides new insights into the phase composition and magnetic behavior of Co$_{2.75}$Fe$_{0.25}$O$_4$ across different annealing temperatures and magnetic field conditions.

Findings

Identification of two-phased cubic spinel structure at lower annealing temperatures.

Confirmation of antiferromagnetic and ferrimagnetic phases via neutron diffraction.

Magnetic field influences phase stability, enhancing low-temperature AFM phase.

Abstract

The low temperature lattice structure and magnetic properties of Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite have been investigated using experimental results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac susceptibility, neutron diffraction and neutron depolarization techniques. The samples have been prepared by chemical co-precipitation of the Fe and Co nitrates solution in high alkaline medium and subsequent thermal annealing of the precipitates in the temperature range of 200- 900 $^\circ$C. Rietveld refinement of the SXRD patterns at room temperature indicated two-phased cubic spinel structure for the samples annealed at temperatures 200-600 $^\circ$C. The samples annealed at temperatures 700 $^\circ$C and 900 $^\circ$C (CF90) have been best fitted with single phased lattice structure. Refinement of the neutron diffraction patterns in the temperature range of 5-300 K confirmed antiferromagnetic (AFM) Co$_3$O$_4$ and ferrimagnetic (FIM) Co$_{2.75}$Fe$_{0.25}$O$_4$ phases for the sample annealed at 600 $^\circ$C and single FIM phase of Co$_{2.75}$Fe$_{0.25}$O$_4$ for the CF90 sample. Magnetic measurements have shown a non-equilibrium magnetic structure, consisting of the high temperature FIM phase and low temperature AFM phase. The magnetic phases are sensitive to magnetic fields, where high temperature phase is suppressed at higher magnetic fields by enhancing the low temperature AFM phase, irrespective of annealing temperature of the samples.