The synthesis and properties of the phases obtained by solid-solid reactions

The presented work encompasses the subject of the studies and the results obtained over the last years by the research workers of the Department of Inorganic Chemistry. They include mainly the studies on the reactivity of metal oxides, searching for new phases in binary and ternary systems of metal oxides as well as describing phase relations establishing in such systems. They also encompass works on the extensive characteristics of physico-chemical properties of the newly obtained compounds

Competing magnetic interactions in Zn3Fe4V6O24 studied by electron paramagnetic resonance

A multicomponent vanadate M3Fe4V6O24 sample with non-magnetic M = Zn(II) ions was synthesized by the solid state reaction method using stoichiometric mixtures of the 80mol% FeVO4 and 20mol% Zn-3(VO4)(2). The temperature dependence of the EPR spectra was performed in the 90-280 K temperature range. The resonance field and the integrated intensity of the EPR line showed minimum value of both parameters at approximate to 200 K. It is suggested that a part of the sample is displaying tendency to form an antiferromagnetic ordered state (or the magnetic clusters) above this temperature while below the ferromagnetic interaction of the main part of material is dominating. This behaviour is attributed to the inherent magnetic inhomogeneity of the system due to the presence of the ferromagnetic or antiferromagnetic spin clusters

Magnetic resonance study of phases in FeVO4Co3V 2O8 system

Multicomponent vanadates Co3xFe4-xV6O 24 have been synthesized using the solid state reaction method from Co3V2O8 and FeVO4.oxides. The electron paramagnetic resonance/ferromagnetic resonance (EPR/FMR) spectra of 20 samples containing solid state phases formed in the FeVO4Co 3V2O8 system have been recorded at room temperature. The howardevansite structure (H-type phase) is produced, which corresponds to the Co2.616Fe4.256V6O 24 formula while a homogeneity range of lyonsite (L-type phase) type structure could be described by the Co31.5xFe4-xV 6O24 formula (0.476<x<1.667). Considering the values of g-factor and linewidth of each registered spectrum the existence of three types of magnetic centers was inferred and correlated with phases detected by XRD method. © 2011 Elsevier B.V. All rights reserved

Competing Magnetic Interactions in Zn3\text{}_{3}Fe4\text{}_{4}V6\text{}_{6}O24\text{}_{24} Studied by Electron Paramagnetic Resonance

A multicomponent vanadate M$\text{}_{3}$Fe$\text{}_{4}$V$\text{}_{6}$O$\text{}_{24}$ sample with non-magnetic M = Zn(II) ions was synthesized by the solid state reaction method using stoichiometric mixtures of the 80mol% FeVO$\text{}_{4}$ and 20mol% Zn$\text{}_{3}$(VO$\text{}_{4}$)$\text{}_{2}$. The temperature dependence of the EPR spectra was performed in the 90-280 K temperature range. The resonance field and the integrated intensity of the EPR line showed minimum value of both parameters at≈200 K. It is suggested that a part of the sample is displaying tendency to form an antiferromagnetic ordered state (or the magnetic clusters) above this temperature while below the ferromagnetic interaction of the main part of material is dominating. This behaviour is attributed to the inherent magnetic inhomogeneity of the system due to the presence of the ferromagnetic or antiferromagnetic spin clusters

Magnetic properties of a new vanadate Cu13Fe4V10O44

A new double vanadate, Cu13Fe4V10O44, obtained by standard solid-state reaction method, has been studied by magnetic susceptibility and electron paramagnetic resonance (EPR) techniques. Measurements of dc susceptibility in ZFC and FC modes in 2-300 K temperature range as well as magnetization in magnetic fields up to 70 kOe have revealed complex magnetic behavior and transition to the antiferromagnetic phase below 2.7 K. The value of the effective magnetic moment calculated from static magnetization measurements was significantly smaller than expected from nominal valences of iron and copper ions indicating strong antiferromagnetic correlations and interactions in clusters or chains of magnetic ions even at high temperature. Although the paramagnetic phase covers a broad temperature range (3-300 K) it differs in many aspects at low and high temperatures. Temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) obtained by fitting the experimental spectrum with Lorentzian lineshape point to the presence of antiferromagnetic dimers in the high-temperature range, strong antiferromagnetic correlations in the paramagnetic phase and critical slowing down of the spin fluctuations on approaching Neel temperature as well as the appearance of magnetically isolated iron ions in the antiferromagnetic phase. © 2015 Published by Elsevier B.V

Study of magnetic inhomogeneity in β-Cu 3Fe 4V 6O 24

The temperature dependence of dc magnetization and electron paramagnetic resonance (EPR) spectra of the β-Cu 3Fe 4V 6O 24 multicomponent vanadate were investigated. Dc magnetic measurements showed the presence of strong antiferromagnetic interactions (Curie-Weiss temperature, Θ ∼ 80 K) at high temperatures, while zero-field-cooled (ZFC) magnetization revealed a cusp-like maximum in low fields at T f1 = 4.4 K, which coincides with the splitting of the ZFC and FC curves. Another maximum was registered at T f2 = 3.0 K. These two temperatures (T f1 and T f2) could be regarded as freezing temperatures in the spin glass state of two magnetic sublattices of Fe1 and Fe2 ions. The EPR spectrum of β-Cu 3Fe 4V 6O 24 is dominated by a nearly symmetrical, very intense and broad resonance line centered at g eff ∼ 2.0 that could be attributed to iron ions. Below 10 K, an additional EPR spectrum with g 1 = 2.018(1) and g 2 = 2.175(1) appears, as well as a very weak line at g eff = 1.99(1). The former spectrum is probably is due to divalent copper ions, and the latter line due to vanadium V 4+ complexes. The temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) was determined in the range of 3-300 K. Two low-temperature maxima in the temperature dependence of the integrated intensity (at 40 and 6 K) were fitted with a function suitable for pairs of exchange-coupled Fe 3+ ions. A comparison of dc magnetic susceptibility and EPR integrated intensity indicates the presence of spin clusters, which play an important role in determining the low-temperature magnetic response of β-Cu 3Fe 4V 6O 24. © Wroclaw University of Technology