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

Abstract (A)[B] 2 O 4 spinel ferrite samples with the composition Cu x 1 Cr x 2 Fe 3− x 1− x 2 O 4 (0.0≤ x 1 ≤0.284 and 1.04≥ x 2 ≥0.656) were prepared by a chemical co-precipitation method. X-ray diffraction patterns indicated that the samples had a single-phase cubic spinel structure. It is interesting that the saturation magnetization of the samples increased when Cu 2+ or Cu 3+ (with 1 or 2μ B of magnetic moment) substituted for Cr 2+ or Cr 3+ (with 4 or 3μ B ), which cannot be obviously explained if the magnetic moments of Cr 2+ and Cr 3+ cations are assumed to be parallel to those of the Fe and Cu cations. However, with the assumption that the magnetic moments of Cr 2+ and Cr 3+ cations are antiparallel to the Fe and Cu cation moments in spinel 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 Cr 2+ and Cr 3+ cations are antiparallel to those of the Fe and Cu cations in spinel ferrites.