Magnetocapacitance as a sensitive probe of magnetostructural changes in NiCr$_2$O$_4$

TL;DR

This study uses magnetocapacitance measurements to sensitively detect magnetostructural changes in NiCr₂O₄, revealing temperature-dependent magnetic and structural transitions and a previously unobserved 20 K anomaly.

Contribution

It demonstrates that magnetocapacitance is an effective tool for probing magnetostructural distortions and uncovers a new magnetic transition at 20 K in NiCr₂O₄.

Findings

Magnetodielectric response varies across three temperature regimes.

Hysteresis in dielectric constant correlates with magnetic hysteresis.

Identification of a new 20 K transition related to ferrimagnetic ordering.

Abstract

The spinel NiCr$_2$O$_4$ is characterized using dielectric and high magnetic field measurements. The trends in the magnetodielectric response fall into three clear temperature regimes corresponding to known magnetic and structural transitions. Above 65\,K, weak magnetic field dependence of the dielectric constant is observed with no hysteresis. When 30\,K\,$\leq\,T\,\leq$\,65\,K, a strong dependence of the dielectric constant on the magnetic field is observed and hysteresis develops resulting in so called butterfly loops. Below 30\,K, magnetodielectric hysteresis is enhanced. Magnetodielectric hysteresis mirrors magnetic hysteresis suggesting that spin-spin interactions are the mechanism for the magnetoelectric effect in NiCr$_2$O$_4$. At high fields however, the magnetization continues to increase while the dielectric constant saturates. Magnetodielectric measurements of NiCr$_2$O$_4$ suggest an additional, previously unobserved transition at 20\,K. Subtle changes in magnetism and structure suggest that this 20\,K anomaly corresponds to the completion of ferrimagnetic ordering and the spin driven structural distortion. We demonstrate that magnetocapacitance is a sensitive probe of magnetostructural distortion.