Ferroelectricity in spiral short-range-ordered magnetic state of spinel MnCr2O4: Significance of topological frustration and magnetoelastic coupling

We report the appearance of ferroelectricity below T-S = 18 K, at which short-ranged spiral spin orders, suggesting that MnCr2O4 is an improper multiferroic material. Linear heat capacity data and zero-field-cooled memory effect verify reentrant spin-glass-like state below T-S. Synchrotron x-ray diffraction studies confirm significant magnetoelastic coupling at long-range ferrimagnetic order (T-N = 42 K) and at T-S. We argue that the release of topological spin frustration, produced due to pyrochlore structure of Cr sublattice, is manifested through the significant magnetoelastic effect at T-N and T-S and holds the key for spiral spin order driven ferroelectricity in MnCr2O4.