Magnetoelectric and Raman spectroscopic studies of single-crystalline MnCr2O4

TL;DR

This study investigates the magnetic and spectroscopic properties of high-quality single-crystalline MnCr2O4, revealing a new magnetic transition, coexistence of spiral spin order and magnetoelectricity, and the effects of magnetic field on phase transition temperatures.

Contribution

First detailed magnetic and spectroscopic analysis of MnCr2O4 revealing a new magnetic transition and coexistence of spiral order and magnetoelectricity.

Findings

Identified a first-order transition from ICSSO to CSSO at 19.4 K

Confirmed coexistence of CSSO and magnetoelectricity below 17.4 K

Observed the phase-transition temperature decreases with increasing magnetic field

Abstract

MnCr2O4 that exhibits spin frustration and complex spiral spin order is of great interest from both fundamental as well as application-oriented perspectives. Unlike CoCr2O4 whose ground state presents the coexistence of commensurate spiral spin order (CSSO) and ferroelectric order, MnCr2O4 shows no multiferroicity. One reason is that the spiral spin order is highly sensitive to the oxygen concentration in MnCr2O4. Here, we have successfully grown high-quality single-crystalline MnCr2O4 by the chemical vapor transport method. We observe a new first-order magnetic transition from the incommensurate spiral spin order (ICSSO) at 19.4 K to the CSSO at 17.4 K. This magnetic transition is verified by magnetization, specific heat, and magnetoelectric measurements, which also confirm that the ground state exhibits the coexistence of the CSSO and magnetoelectricity below 17.4 K. Interestingly, the temperature evolution of Raman spectra between 5.4 and 300 K suggests that the structure remains the same. We also find that the phase-transition temperature of the CSSO decreases as applied magnetic field increases up to 45 kOe.