Understanding the correlation between orbital degree of freedom, lattice-striction and magneto-dielectric coupling in ferrimagnetic Mn1.5Cr1.5O4

Abstract

Dielectric anomaly observed in cubic Mn_1.5Cr_1.5O₄around ferrimagnetic ordering temperature (T_N) suggests a possible magneto-dielectric coupling in the system. This report confirms the presence of a weak but significant magneto-dielectric coupling in the system. Theab initiocalculations show a band gap of around 1.2 eV, with Fermi-level closer to the conduction band. The major features of conduction band nearest to the Fermi-level correspond tod_xzandd_3z²_-r²orbitals of Mn³⁺ion. Temperature-dependent neutron diffraction results show a rapid decay in structural parameters (lattice-striction and transition metal-oxygen bond length) aroundT_N.We confirmed that these changes in structural parameters atT_Nare not related to structural transition but the consequences of orbital-ordering of Mn³⁺. The rapid decay in transition metal-oxygen bond length under internal magnetism of the system shows that magnetism could certainly manipulate the electric dipole moment and hence the dielectric constant of the system. Magneto-striction acts as a link between magnetic and dielectric properties.

Keywords: electronic structure; ferrimagnetism; magneto-dielectric effect; x-ray photoemission spectroscopy.