New ( αβγ )-incommensurate magnetic phase discovered in the MnCr2O4 spinel at low temperatures

Abstract

The nuclear and magnetic structure of the spinel $\mathrm{Mn}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ is reinvestigated by magnetization, specific heat, and neutron diffraction experiments at different temperatures. Four samples of this spinel synthesized under different atmospheres are analyzed. Through these experiments, a new magnetic phase, with propagation vector ${\stackrel{P\vec}{k}}_{\mathrm{I}2}=(0.6597(1)\phantom{\rule{0.16em}{0ex}}0.5999(1)\phantom{\rule{0.16em}{0ex}}0.1996(2))$, not previously reported, is identified below 18 K when the sample is synthesized under a reductive atmosphere. A possible explanation for the different magnetic ground states observed is given based on the competition among the main exchange interactions present in the system. Using the magnetic superspace group formalism, the symmetry of the nuclear and magnetic structures is determined. The presence of transverse conical magnetic structures in the lower-temperature phases allows for multiferroicity in this compound, and the electric polarization direction is determined for each magnetic phase.