Simultaneous enhancement of magnetocaloric and magnetodielectric effects in MnCo2O4 spinels by varying the Co/Mn ratio

Abstract

Polycrystalline MnCo₂O₄ and Mn_1.25Co_1.75O₄ ceramics are successfully synthesized by a solid-state reaction method, and their structure, chemical states, magnetic properties, magnetocaloric effect and magnetodielectric properties are investigated systematically. It is found that both ceramics undergo a ferrimagnetic to paramagnetic phase transition, corresponding to the second-order magnetic phase transition, confirmed by the Belov–Arrott plot measurement and the normalized magnetic entropy as a function of rescaled temperature. Furthermore, the observed spin glass behavior can be proved by the ac-magnetic susceptibility, magnetization versus temperature measured at various magnetic fields under the zero-field-cooling process, isothermal remnant magnetization and the memory effect. It is worth noting that enhanced ferrimagnetism is observed in Mn_1.25Co_1.75O₄ ceramics with a higher Curie temperature of 187 K and a larger remnant magnetization (2M_r) of about 33.20 emu g⁻¹ at 10 K. Its large magnetocaloric effect is obtained with a maximum magnetic entropy change of 2.04 J kg⁻¹ K⁻¹ and a relative cooling power value of 71.14 J kg⁻¹ under 5 T. The critical exponents have been derived from the modified Arrott plots and the Kouvel–Fisher method, indicating that both ceramics follow the mean-field model. Particularly, a significant dielectric anomaly appears in the vicinity of the ferrimagnetic Curie temperature, exhibiting an intrinsic magnetodielectric coupling behavior. The underlying physical mechanism could be attributed to the strong magnetic properties owing to the competition among J_AA, J_BB and J_AB interactions, which is influenced by the increase of the Mn³⁺ ion proportion. The present work highlights the potential of MnCo₂O₄-based spinels as promising candidates for intermediate temperature magnetic refrigerants.