The temperature dependent dc resistivity of spinel Mn1.56Co0.96Ni0.48O4 (MCN) films is measured in the range of 130–304 K. The hopping exponent p of small polaron hopping conduction shows a clear variation from a value of 0.46 in the paramagnetic to 0.91 in the ferromagnetic phase. In order to explain such variation, a model is proposed where Gaussian distributed localized electron states gradually withdraw from the Hubbard band gap below the magnetic transition as a result of increased magnetic order. This correlation between hopping conduction and magnetic order in MCN films may provide a possible approach to fabricate the devices which couple magnetic and electronic properties in one unit.

The serial films of Mn2.52−xCoxNi0.48O4 (x=0, 0.32, 0.64, and 0.96) with fixed Ni content of 0.48 are prepared on amorphous Al2O3 substrate by chemical solution deposition method. The x-ray diffraction and microstructure analyses indicate that Co/Mn content ratio can modify the preferred crystalline growth direction and the microstructure morphology of different composition is different under the same growth condition. The distribution of the cations for the four compositions is estimated based on the lattice constant and cation radii. The dc resistivity measurements demonstrate our speculation of the cation distributions. The electrical and magnetic measurements show that the thermal activation energy decreases but the ferrimagnetic transition temperature increases with the increase in Co content. The magnetization loop tests indicate that Mn2.52−xCoxNi0.48O4 serial films probably possess magnetic anisotropy with ⟨111⟩ magnetically easy axis.

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