Multiferroicity in the Presence of Exchange Bias: The Case of Spinel CoMn ₂ O ₄

Ferrimagnetic spinel materials of formula AB 2 X 4 , where A and B are transition metals and X is oxygen or sulfur, hold promise for the realization of multiferroic characteristics. Herein, synthesis of spinel CoMn 2 O 4 is reported and its magnetic, dielectric, and ferroelectric aspects and their correlations are explored. Polycrystalline CoMn 2 O 4 is synthesized by using the conventional solid‐state method. The X‐ray diffraction and Raman spectroscopy confirm the phase purity of the synthesized compound. The crystal structure is identified with tetragonal symmetry (I41/ amd space group). DC magnetization measurements indicate two magnetic transitions: one at temperature T 1 ≈ 186 K, followed by another Yafet–Kittel ferrimagnetic transition at T 2 ≈ 86 K. A frequency‐independent anomaly in the temperature‐dependent dielectric permittivity is observed near the low magnetic ordering temperature ( T 2 ). This reflects the possibility of the correlation between lattice dynamics and spin ordering in spinel CoMn 2 O 4 . A substantial exchange bias is also observed below T 2 ≈ 86 K. The change in dielectric permittivity in the presence of applied magnetic field follows the square of the magnetization dependence, which is consistent with Ginzburg–Landau theory. However, the detailed pyroelectric current measurements reveal the absence of intrinsic ferroelectric order.