Study of the magnetic structure and the cation distributions in MnCo spinel ferrites

Single-phase powder samples of the spinel ferrites MnxCo1−xFe2O4 (0.0≤x≤0.3) were prepared using a conventional co-precipitation method. Comparing with the samples CrxNi1−xFe2O4 (0.0≤x≤0.3) reported recently by our group, we found that there are two different trends in the magnetic moments (μexp) per formula of samples measured at 10 K: the value of μexp increased when Mn (Mn2+ with 3d5 electron configuration) substituted for Co (Co2+ with 3d7 electron configuration), while μexp decreased when Cr (Cr2+ with 3d4) substituted for Ni (Ni2+ with 3d8). The dependences of μexp on the doping level x for the two series of samples were fitted successfully, using the quantum-mechanical potential barrier model earlier proposed by our group. In the fitting process, the magnetic moment directions of the Cr3+, Cr2+ and Mn3+ cations were assumed to be antiparallel to those of the other cations in the same sublattices due to constraints arising from Hund's rules.