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

Abstract

Iron-containing ceramic materials based on BiNbO 4 of orthorhombic modification were obtained by solid-phase synthesis. Solid solutions α-BiNb 1−x Fe x O 4−δ were synthesized in the narrow concentration interval of х ≤ 0.03. The single-phase structure of the samples prepared was determined by X-ray diffraction and SEM-analyses. In the electron paramagnetic resonance (EPR) spectra of BiNb 1−x Fe x O 4−δ , a wide band with the center at g = 2.16-2.37 was observed, and a low-intensity signal with g-factor of about 4.3 was recorded on its low-field wing. Along with the broad spectrum component, a "noise-like" signal formed by a large number of narrow lines related to the integral signal of ferromagnetic resonance (FMR) and its fine structure was observed in the magnetic field range of 190-400 mT. Based upon measurements of magnetic susceptibility, the paramagnetic components and the effective magnetic moment values of iron atoms at different temperatures and for different concentrations of solid solutions were calculated. The isotherms of the paramagnetic component of the magnetic susceptibility of iron atoms in BiNb 1−x Fe x O 4−δ were typical of antiferromagnets. The value of the effective magnetic moment of iron atoms increased with the rise in temperature from 5.84 μB at 90 K to 6.43 μB at 320 K. This can be explained by the presence of exchange-bonded aggregates of Fe (III) atoms with antiferromagnetic and ferromagnetic types of exchange in the solid solutions. The magnetic behavior of BiNb 1−x Fe x O 4−δ was investigated by theoretical calculation of magnetic susceptibility within the framework of the model of diluted solid solutions taking into account the presence of possible types of clusters of iron atoms. The best agreement between the experimental and calculated data was obtained for the dimer parameters of J dim = −17 cm −1 and J dim = 45 cm −1 for the antiferromagnetic and ferromagnetic types of exchange.

Formation of Fe–Fe Antiferromagnetic Dimers in Doped TiO2:Fe Nanoparticles

“…For example, in Mn-doped GaN systems concentration-independent AFM exchange of the order −1.624 K was observed . Moreover, one can expect in the imperfect areas, the appearance of dimers with positive exchange that, perhaps, some authors observe even at as-prepared state without undesirable phases. , …”

“…63 Moreover, one can expect in the imperfect areas, the appearance of dimers with positive exchange that, perhaps, some authors observe even at asprepared state without undesirable phases. 16,64 ■ SUMMARY AND CONCLUSION In summary, a series of TiO 2 :Fe-type samples with different Fe content have been synthesized by a low-temperature sol−gel method and subsequently subjected to the etching in 2 M HCl. It has been shown that etching of the samples in hydrochloric acid completely removes impurity phases as well as their ferromagnetic contribution.…”

High-Temperature Crystal Chemistry of α-, β-, and γ-BiNbO4 Polymorphs

“…Bismuth orthoniobate (BiNbO 4 ) is still of interest after more than half a century due to its microwave dielectric and photocatalytic properties. , BiNbO 4 ceramics containing V 2 O 5 and CuO have excellent dielectric properties, as was shown for the first time in the work revealing high values of the quality factor Q r = 4260 (at 4.3 GHz), dielectric constant ε r = 43, and the coefficient of resonant frequency t f = +38 ppm/°C. In order to obtain high-density ceramics and optimize the dielectric properties of bismuth orthoniobate, sintering additives are added and bismuth or niobium atoms are substituted hetero- and isovalently. − The low temperature of the synthesis (∼1000 °C) of bismuth orthoniobate materials promotes their use as dielectrics for multilayer microwave circuits with silver (copper) inner conductors. Thus, bismuth orthoniobate materials facilitate miniaturization of the resonant devices…”

Influence of alkaline earth metal atoms on magnetic properties of Bi2MNb2−2xFe2xO9−δ (M — Ba, Sr, Ca)

“…В формуле (1) независимыми параметрами являются доли кластеров с ферро-и антиферромагнитным типом взаимодействия, а также неявно входящие в формулу параметры ферро -и антиферромагнитного обмена между атомами железа (III) в димерах и тримерах. Формулы для расчета магнитной восприимчивости димеров и тримеров по модели Гейзенберга-Дирака-Ван-Флека [24] и согласования рассчитанных и экспериментальных значений магнитной восприимчивости твердых растворов приведены в работах [18,19].…”