Magnetodielectric effect in CoCr_2-XFe_XO₄

Conventional multiferroics show the multiferroic behaviors below two successive transitions (a ferroelectric transition and a ferromagnetic transition). In the present study, we report the magneto-dielectric (MD) effect (both in-plane and out-of-plane) in CoCr_2-XFe_XO ₄ which undergoes only a ferromagnetic transition. We found the MD effect in the pure ferromagnetic phase (T_S<T<T_C) of CoCr₂O₄. And such MD effect is temperature dependent. The magnitude of the MD effect gradually decreases with approaching Curie temperature (T_C) and finally becomes zero at T_C. With doping Fe into CoCr₂O₄, we found the magnitude of MD effect increases and the MD effect exists in a wider temperature region because T_C increases and T_S decrease with doping Fe. Our results show the coupling between the ferromagnetic and ferroelectric orders. It suggests that both the ferromagnetic and ferroelectric properties originate from the same transition.