Magnetodielectric coupling in MnCr2O4 spinel

We have investigated the magnetic and dielectric properties of polycrystalline samples of the spinel MnCr2O4. Below the ferrimagnetic ordering temperature at T-N similar to 43 K, both magnetization and dielectric measurements show signatures of the onset of a conical structure at T-s similar to 17 K and a lock-in temperature at T-f similar to 14 K. These values are similar to those previously reported for single-crystal samples, where the spiral structure is short-range ordered (SRO) at low temperatures. The application of magnetic field suppresses the dielectric anomaly at T-f indicating that the coherence length of the ordering increases. MnCr2O4 exhibits a symmetrical magnetodielectric response between T-f and T-s that scales with the square of the magnetization. This suggests that the magnetodielectric coupling originates from the (PM2)-M-2 term in the free energy expansion. The magnetodielectric response becomes asymmetric with respect to field below T-f. (C) 2009 Elsevier B.V. All rights reserved.