Electron paramagnetic resonance and magnetic properties of α-BiNb1−xFexO4−δ

Abstract

Iron-containing ceramic materials based on BiNbO4 of orthorhombic modification were obtained by solid-phase synthesis. The solid solutions α-BiNb1-xFexO4-δ were synthesized of х ≤ 0.03. The single-phase structure of these samples was established by X-ray diffraction and SEM- analyses. In the EPR spectra of BiNb1-xFexO4-δ, a wide band with a center at g = 2.16–2.37 were observed, which had a low-intensity signal with a g-factor of ~ 4.3 on the low-field wing. Along with the broad spectrum component, a "noise-like" signal was observed in the magnetic field range of 190-400 mT, which was formed by a large number of narrow lines related to the integral signal of ferromagnetic resonance and its fine structure. The isotherms of the paramagnetic component of the magnetic susceptibility of iron atoms in BiNb1-xFexO4-δ are typical for antiferromagnets. The value of the effective magnetic moment of iron atoms increases along with the increase in temperature from 5.84 MB (90 K) to 6.43 MB (320 K). This can be explained by the presence of exchange-bound aggregates of Fe (III) atoms with the antiferro- and ferromagnetic types of exchange in the solid solutions. Magnetic behavior of BiNb1-xFexO4-δ was investigated taking into account the presence of possible types of clusters of iron atoms by theoretical calculation of the magnetic susceptibility within the framework of the model of dilute solid solutions. The best agreement between the experimental and calculated data was obtained for the dimer parameters of Jdim - 17 cm-1 and Jdim 45 cm-1, for antiferro-and ferromagnetic type of exchange.