The EPR spectrum of (Formula presented) ions in (Formula presented) 0.5) is studied as a function of temperature. In the oxygen-deficient superconducting phase, the (Formula presented) EPR spectrum comprises a broad EPR line described by a rhombic g tensor and anisotropic linewidths along the principal axes. Analysis of the EPR linewidth provides an estimate for the effective isotropic exchange interaction, (Formula presented) between (Formula presented) ions, indicating that the magnetic ordering of the (Formula presented) sublattice is determined by the interplay between the short-range exchange interactions and the long-range dipole-dipole interactions. © 1998 The American Physical Society.

The temperature dependence of the EPR spectrum for the α-phase of iron tungstate has been investigated in the temperature range of 40-260 K. At temperatures between T1 ≈ 250 K and T2 ≈ 205 K where the antiferromagnetic phase transition occurs, a relatively narrow EPR line arising from the dominant iron(III) species has emerged, gaining intensity with the temperature increase. Its linewidth temperature evolution could be described by Huber equation, with TN = 200 K, which is consistent with the peak seen in magnetic susceptibility measurements, while the corresponding g-factor shifts to higher fields reflecting the build-up of internal field emerging from increasing short-range order in the spin system. At temperatures lower than T2, a very broad and distorted EPR line with temperature dependent g-factor and linewidth has been observed reflecting the corresponding rise of the magnetic susceptibility below the antiferromagnetic phase transition, presumably arising from magnetic clusters embedded in the antiferromagnetic background. © Springer-Verlag 1998.

{The temperature dependence of the EPR spectra of the recently discovered Ag6S3O4 phase in the Ag-O-S system prepared by two methods, the known method of co-precipitation from aqueous solution and a new method depending on the interaction of Ag2S and Ag2SO4 solid reagents, has been investigated. No EPR spectra were observed at room temperature, while at liquid helium temperature a number of EPR spectra have been recorded, which disappeared upon increasing temperature up to liquid nitrogen temperature. The sample obtained by the co-precipitation method revealed an intense, rich EPR spectrum that has been tentatively interpreted assuming the presence of at least two different Ag2+ ion complexes, one monomer resulting in an intense anisotropic, rhombic EPR powder pattern with g1 = 1.93(1)

The temperature dependence of the magnetic, electrical conductivity, and electron paramagnetic resonance (EPR) properties of Fe8V10W16O85has been investigated. The magnetic susceptibility measurements revealed an almost Curie-Weiss law behavior above room temperature and an additional magnetic interaction at low temperature, causing a steep rise of magnetization as the liquid helium temperature was approached. The value of the magnetic moment at high temperature,μeff=1.80μB, suggests a predominance of trivalent iron ions in a low-spin state. In the 300-4.2 K temperature range a difference between the zero field cooling (ZFC) and the field cooling (FC) modes was recorded. This irreversible behavior might be related to the presence of weakly coupled clusters. The EPR measurements revealed a broad, temperature-dependent resonance line at high temperature and two weaker lines at low temperature. The two low-temperature lines were attributed to antiferromagnetically coupled high-spin Fe3+ion clusters and to high-spin iron ions placed at sites with low symmetry of the crystal field. The broad line at high temperature was separated into two Lorentzian lines. These component lines were attributed to the two paramagnetic centers connected with the Fe3+ions involved in the magnetic structure of Fe8V10W16O85: dominant low-spin centers and a small admixture (<15%) of the high-spin centers. The line broadening and shift of the resonance field of the two component lines with decreasing temperature were studied and analyzed using a model of the EPR lines of antiferromagnets. The temperature dependence of the electrical conductivity showed a typical semiconducting-type behavior with an activation energy of 0.40 eV. The hopping mechanism of small polarons was proposed to explain the transport properties of the sample. © 1998 Academic Press.

The electron paramagnetic resonance (EPR) linewidth of (Formula presented) in (Formula presented) is studied as a function of Er concentration. The EPR spectrum complies with the crystal-field ground doublet, while linewidth analysis shows the presence of exchange narrowing. Comparison of the theoretical EPR linewidth with the experimental data provide evidence for the presence of nearest-neighbor exchange interactions of the order of 1 K, most probably anisotropic along the a and b crystallographic axes. © 1998 The American Physical Society.