Magnetodielectric effect from the onset of ferrimagnetic transition in CoCr ₂O ₄

Multiferroicity in CoCr ₂O ₄ is generally regarded to emerge from the onset of noncollinear spiral magnetic order (T _s ≈ 28K) due to the inverse Dzyaloshinskii-Moriya interaction, far below the temperature of collinear ferrimagnetic transition (T _c ≈ 96K). So far, the possibility of multiferroicity appearing in collinear magnetic order has been rarely explored. Here, we report a magnetodielectric effect emerging from the onset of collinear ferrimagnetic transition T _c in CoCr ₂O ₄. Based on the postulation of non-centric crystal symmetry and Landau theory, we deduce that such a magnetodielectric effect is attributed to the coexistence of electric and magnetic ordering by the magnetoelectric coupling below T _c. Our results suggest that CoCr ₂O ₄ is a natural multiferroic in both noncollinear spiral and collinear magnetic ordering.