Jahn-Taller Distortion on Exchange Interactions between Cations in Mn_xCu_1-xCo₂O₄ System

Abstract Pure-phase MnxCu1-xCo2O4 (x=0, 0.25, 0.5, 0.75 and 1) polycrystalline powders were prepared by using a low-temperature solid-phase reaction method. With doping Mn ion into the octahedral sites, the unit cell transforms from cubic phase to tetragonal phase, and the octahedral Co3+ ions move to the tetrahedral sites and become high spin Co2+ ions. When the doped Mn concentration is low, the sample is dominated by antiferromagnetic interactions between tetrahedral Cu2+. As the Mn concentration increases, ferrimagnetic interactions between tetrahedral Co2+ and octahedral Mn3+ can be observed. When the Mn concentration is high enough, due to strong Jahn-Taller distortion, the eg energy level of Mn splits, which weakens the interactions between the tetrahedral and the octahedral cations, and enhances interactions between the octahedral cations. Ferromagnetic interactions between octahedral Mn3+ and antiferromagnetic interactions between octahedral Mn2+ become obvious. The magnetic ordering temperature has been raised from 20 K to 93 K as the Mn concentration increases, and the maximum exchange bias field is observed to be 1.063 kOe.