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 t2 g or eg orbitals of the transition metal on the octahedral site, a critical decrease of ε1 and Δ L / L at the ferrimagnetic transition temperature (TN) was observed. On the other hand, MnCr2 O4 which has no orbital degree of freedom, anomalies in ε1 and Δ L / L at TN 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.
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