Mechanism of Cu dopant in transition metal oxide Mn_1.56Co_{(0.96- x )}Ni_0.48Cu_xO_4+δ (0 ≤ x ≤ 0.2) thin films

To identify the substitution of Cu element for cations in transition metal oxide AB₂O₄ structure, we propose to investigate the structural, optical and magnetic properties of Cu-doped Mn_1.56Co_{(0.96- x )}Ni_0.48Cu_xO_4+δ films with 0 ≤ x ≤ 0.2. The X-ray diffraction of Mn_1.56Co_{(0.96- x )}Ni_0.48Cu_xO_4+δ films indicates good crystallization and cubic spinel structure. Raman spectra show two peaks of F_2g and A_1g vibration modes, and the peak position changes with Cu dopant. The transition temperatures T_P1, T_P2 shift towards lower temperature by Cu doping, and the saturation magnetization M_S decreases monotonously. The results show that the substitution of Cu ions does not vary the crystal structure but changes the ratio of Mn³⁺/Mn⁴⁺. Our proposed way overcomes the difficulties to directly observe the atoms of Mn, Co, Ni, and Cu with closed sizes in microstructure, and it is instructive to further understand the conduction mechanism of doped manganese cobalt nickel oxides in theory.