Correlation between magnetic, dielectric properties and crystal structure in Mn T₂ O₄ (T = V, Cr, Mn)

We measured the temperature dependence of dielectric constant (ε₁) and lattice striction (Δ L / L) for MnV₂ O₄, Mn₃ O₄, and MnCr₂ O₄. For MnV₂ O₄ and Mn₃ O₄, which have the orbital degree of freedom in the t_{2 g} or e_g orbitals of the transition metal on the octahedral site, a critical decrease of ε₁ and Δ L / L at the ferrimagnetic transition temperature (T_N) was observed. On the other hand, MnCr₂ O₄ which has no orbital degree of freedom, anomalies in ε₁ and Δ L / L at T_N are barely observed. These results indicate that the orbital degree of freedom is a key factor for the correlation between magnetic, dielectric properties and crystal structure in the series of Mn T₂ O₄.