Study on cation distribution and magnetic moment of Ti ions in spinel ferrites Ni1-xTixFe2O4

Abstract

Spinel ferrite samples TixNi1-xFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4) were prepared using conventional solid reaction method. The sample exhibit a single-phase cubic spinel structure with a space group obtained Fd3m. The lattice parameter a increases with the increase of Ti doping level x. But the specific saturation magnetizations, σs, gradually decrease with increasing Ti doping level x at 10 K and 300 K. It is interesting that when the doping level x≥0.2, two transition temperatures, TL and TN, are found: when the temperature is lower than TN, the magnetization is obviously decreased, while at the temperature TL, dσ/d T reaches a maximum value. This phenomenon indicates that an additional antiferromagnetic structure arises in the traditional spinel phase of ferrites which results from Ti doping, that Ti ions will show the form of Ti3+ and Ti2+ cations which have magnetic moments, and that the magnetic moments of the Ti cations are opposite to those of the Fe and Ni cations. The dependence of the magnetic moments of the samples on the Ti doping level x at 10 K was fitted successfully using the quantum-mechanical potential barrier model proposed earlier by our group. In the fitting process, the distributions of Ti, Ni and Fe cations in the samples are obtained. It is found that 80% of the Ti cations will occupy the [B] sites in Ti2+ form.