Structural and magnetic properties of CoFe1.9RE0.1O4 (RE=Y, La) prepared by a sol–gel method

Abstract Ultrafine CoFe 1.9 RE 0.1 O 4 (RE=Y, La) powders have been fabricated by a sol–gel method. Structural and magnetic properties of the powders were investigated by X-ray diffractometer, Mossbauer spectroscopy, and vibrating sample magnetometer. The CoFe 1.9 Y 0.1 O 4 powders that were fired at and above 923 K contained only a single spinel phase and behaved ferrimagnetically. Powders fired at 723–823 K had a spinel structure and were mixed paramagnetic and ferrimagnetic in nature. Mossbauer spectra of the CoFe 1.9 Y 0.1 O 4 powder fired at 923 K were taken at various temperatures ranging from 18 to 865 K. The iron ions at both A (tetrahedral) and B (octahedral) sites were found to be in ferric high-spin states. The Neel temperature T N was found to be 865±2 K. Debye temperatures for A and B sites were found to be Θ A =695±5 K and Θ B =279±5 K, respectively. The magnetic behaviors of the CoFe 1.9 Y 0.1 O 4 powders fired at and above 1123 K and CoFe 1.9 La 0.1 O 4 powders fired at and above 923 K, respectively, showed that an increase of the firing temperature yielded a decrease in the coercivity and an increase in the saturation magnetization. The maximum coercivity and the saturation magnetization were H c =1208 Oe and M s =69 emu/g in the CoFe 1.9 Y 0.1 O 4 samples and H c =703 Oe and M s =72 emu/g in the CoFe 1.9 La 0.1 O 4 samples.