Magnetism evolution in Ni-doped Co3O4

Pure phase Ni-doped Co 3 O 4 nanoparticles (Ni x Co 3-x O 4 , 0≤x ≤ 1) were prepared using a hydrothermal method . At low doping concentrations, Ni preferentially enters the octahedral sites to replace the non-magnetic Co 3+ , and a new superexchange interaction is created between tetrahedral Co 2+ and octahedral Ni 3+ . A spin glass state was observed. The magnetic transition temperature of the Ni x Co 3-x O 4 powders significantly increases from 36 K to 236 K, and the saturation magnetization increases to 2.239 μ B /f.u. As the Ni content continues to increase, and Ni ions unexpectedly enter tetrahedral sites and new superexchange interactions are emerged. However, the superexchange interaction between tetrahedral Ni 2+ and octahedral Ni 3+ is weaker than that between tetrahedral Co 2+ and octahedral Ni 3+ . Meanwhile, tetrahedral Ni 2+ makes octahedral Co 3+ transform from low spin to high spin, resulting in a decrease in the total magnetization of the sample.