Impact of Ir4+ with single-ion anisotropy on magnetic properties of Mn1−xIrxCo2O4

Abstract The Mn1−xIrxCo2O4 spinel crystallizes in the cubic structure with the space group Fd-3 m. The doped Ir4+ with strong spin-orbit coupling has a significant impact on the magnetic properties of Mn1−xIrxCo2O4. The Ir4+ ion shares the B site with the Mn3+ and Co3+ ion. A metamagnetic transition is observed in the samples with x = 0 and 0.05. One FM, which slightly varies in the range of 166 K–158 K for 0 ≤ x ≤ 0.3, and one AFM, which increases from 133 K to 147 K with 0.1 ≤ x ≤ 0.3 are observed. The sample of x = 0.3 has one more AFM and one more FM transition. The exchange coupling of the FM with the AFM induces the enhanced coercivity and the exchange bias with magnetic frustrations. The coercive field of Mn1−xIrxCo2O4 increases greatly from almost zero for x = 0 to 0.52 T with the doped Ir4+ content as low as 0.05. It suggests that the Ir4+ ion possesses a strong single-ion anisotropy. The sample of x = 0.2 has the highest coercive field of 0.82 T due to the exchange coupling of the AFM and FM interactions. The exchange bias effect is observed in x = 0.05 after FC at 0.5 T, in x = 0.1 at both the ZFC and FC state, and in x = 0.3 at the ZFC state, but not in x = 0.2. The enhanced coercivity and observed exchange bias effect are resulted from the exchange coupling between a ferromagnet (FM) and uncompensated spins or frustrated spins at the interfacial region of an antiferromagnet (AFM).