Experimental evidence for the magnetic moment directions of Cr2+ and Cr3+ cations in the spinel ferrites Cux1Crx2Fe3-x1-x2O4

(A)[B](2)O-4 spinet ferrite samples with the composition Cux1Crx2Fe3-x1-x2O4 (0.0 <= x(1) <= 0.284) were prepared by a chemical co-precipitation method. X-ray diffraction patterns indicated that the samples had a single-phase cubic spinet structure. It is interesting that the saturation magnetization of the samples increased when Cu2+ or Cu3+ (with 1 or 2(mu B) of magnetic moment) substituted for Cr2+ or Cr3+ (with 4 or 3(mu B)), which cannot be obviously explained if the magnetic moments of Cr2+ and Cr3+ cations are assumed to be parallel to those of the Fe and Cu cations. However, with the assumption that the magnetic moments of Cr2+ and Cr3+ cations are antiparallel to the Fe and Cu cation moments in spinet ferrites, the dependence on the Cu doping level of the sample magnetic moments at 10 K was fitted successfully, using the quantum-mechanical potential barrier model earlier proposed by our group. Using the cation distributions obtained in the fitting process, the experimental observation that the magnetic moment of the samples increased with increasing Cu doping level was explained. This work therefore provides experimental evidence that the magnetic moments of the Cr2+ and Cr3+ cations are antiparallel to those of the Fe and Cu cations in spinet ferrites. (C) 2014 Elsevier B.V. All rights reserved.