Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase NixMn1-xCo2O4 (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of NixMn1-xCo2O4 increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni0.5Mn0.5Co2O4 sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in NixMn1-xCo2O4 (x = 0 and 0.25), and as the concentration of Ni increases, NixMn1-xCo2O4 (x = 0.75 and 1) show a spin glass state. The structure of NixMn1-xCo2O4 (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in NixMn1-xCo2O4 and that the strength of the Ni-O bond is greater than that of the Mn-O bond.