Jahn–Taller distortion on exchange interactions between cations in Mn x Cu1−x Co2O4 system

Abstract

Pure-phase Mn x Cu1−x Co2O4 (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 (AFM) 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 e g 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 AFM 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.