Co 0.8 Mn x Fe 2.2 − x O 4 (x=0.2, 0.4, 0.6, and 0.8) powders were prepared by a sol-gel process and annealed at different temperatures (Ta=600, 800, 1000, and 1200 °C). X-ray diffractometer results reveal that all the samples are inverse-type spinel with cubic structure. The magnetic properties were measured by vibrating sample magnetometer and the results indicate that the saturated magnetization (Ms) and coercivity (Hc) decrease with increasing Mn content x. The decrease in Ms is related to the magnetic moment of Mn3+ is lower than that of Fe3+. The decrease in Hc is ascribed to the content decrease in Co2+ on B sites. Increasing grain sizes at higher annealing temperature (Ta) also have an intensive influence on Hc.

On the basis of the perturbation formulas for a d 1 configuration ion in a tetragonal crystal field, the three optical absorption bands and electron paramagnetic resonance (EPR) parameters (g factors g i and hyperfine structure constants A i for i = and ⊥, respectively) of VO 2+ in Na 3 C 6 H 5 O 7 · 2H 2 O single crystals were studied using the perturbation theory method. By simulating the calculated optical and EPR spectra to the observed values, local structure parameters and negative signs of the hyperfine structure constants A i of the octahedral (VO 6 ) 8− cluster in trisodium citrate dehydrate single crystal can be obtained.