Annealing effect on the structural and magnetic properties of the CuAl 0.6 Cr 0.2 Fe 1.2 O 4 nano-ferrites

Abstract Amounts of the as-synthesized CuAl0.6Cr0.2Fe1.2O4 nanoparticles by the chemical co-precipitation method were annealed for 4 h at one of the temperatures TA = 300, 500, 600, 800 and 1000 °C for each. The techniques used for characterizing the samples were X-ray diffractions, infrared (IR) and Mossbauer spectroscopy and vibrating sample magnetometer. This study proved single-phase cubic structure of the samples annealed at TA ≤ 800 °C and tetragonal structure of the sample annealed at 1000 °C. The cubic-to-tetragonal structure transformation was attributed to the tetragonal distortion by Jahn–Teller effect (JTE) of Cu2+ ions. This study revealed that all deduced parameters were affected by JTE, whereas the crystallite size, lattice parameters, strain, threshold frequency, force constants, Debye temperature and stiffness constant were dependent on TA. IR absorption band positions and intensities were dependent on TA and proved the existence of Fe2+, Fe4+ and Cr4+ ions in the crystal sublattices. The spontaneous and saturation magnetization and hyperfine magnetic field of the tetrahedral and octahedral sites were deduced and discussed as functions of TA.