Magnetodielectric effects in A-site cation-ordered chromate spinels LiMCr4O8 (M = Ga and In)

Abstract

We report the occurrence of a magnetodielectric effect and its correlation with structure and magnetism in the A-site ordered chromate spinel oxides LiMCr4O8 (M = Ga, In). In addition to magnetic and dielectric measurements, temperature dependent synchrotron and neutron diffraction experiments have been carried out for the Ga compound. The results are compared and contrasted with that of a corresponding conventional B-site magnetic chromate spinel oxide, ZnCr2O4. Like ZnCr2O4, the A-site ordered chromate spinels exhibit a magnetodielectric effect at the magnetic ordering temperature (T-N similar to 13-15 K), resulting from magnetoelastic coupling through a spin Jahn-Teller effect. While the presence of a broad magnetic anomaly, associated with a short-range magnetic ordering (T-SO similar to 45 K) in ZnCr2O4, does not cause any dielectric anomaly, a sharp change in dielectric constant has been observed in LiInCr4O8 at the magnetic anomaly, which is associated with the opening of a spin gap (T-SG similar to 60 K). Contrary to the In compound, a broad dielectric anomaly exists at the onset of short-range antiferromagnetic ordering (T-SO similar to 55 K) in LiGaCr4O8. The differences in dielectric behavior of these compounds have been discussed in terms of breathing distortion of the Cr-4 tetrahedra.