Magnetic properties of Y-, La-, Nd-, Gd-, and Bi-doped ultrafine CoFe2O4 spinel grown by using a sol-gel method

Y-, La-, Nd-, Gd-, and Bi-doped ultrafine CoFe2O4 particles are fabricated by using a sol-gel method. Magnetic and structural properties depending on annealing temperature of powders are investigated with X-ray diffractometer (XRD), Mossbauer spectroscopy, and vibrating sample magnetometer (VSM). Y-, Gd-, and Bi-doped samples fired at and above 923 K have only a single cubic spinel strcture and behave ferrimagnetically, but in La- and Nd-doped samples alpha-Fe2O3 phase was observed at and above 1123 K. Powders annealed at 823K have a typical spinel structure and have a paramagnetic and ferrimagnetic nature, simultaneously. The isomer shifts of all samples indicated that the iron ions were ferric at the tetrahedral [A] and the octahedral sites CBI, respectively. The magnetic behavior of CoFe1.9Bi0.1O4 and CoFe1.9Nd0.1O4 spinel powders fired at and above 923 a shows that an increase of the annealing temperature yields a decrease of the coercivity and an increase of the saturation magnetization. The highest coercivity of 1358 Oe and saturation magnetization of 76.2 emu/g are observed in CoFe1.9Bi0.1O4 compound. (C) 2000 Elsevier Science B.V. All rights reserved.