S. Filip

EPR and magnetic susceptibility studies of iron ions in 70TeO2·25B2O3·5PbO glass matrix

Abstract Results of EPR and magnetic susceptibility measurements performed on xFe2O3·(1 − x)[70TeO2·25B2O3·5PbO] glasses with 0 1 mol.%. The spectra of the investigated glasses containing up to 3 mol.% Fe2O3 presents in addition to the line at g ≈ 4.3 also a weak resonance line at g ≈ 9.79 that denotes the rhombic character of the structural units involving the resonance centers. The paramagnetic resonance data consists with those obtained from magnetic measurements. The Curie constant values indicate that in this glass system the iron ions are in both Fe3+ and Fe2+ valence state, the last one representing about 56% from the total iron ions content. For x ≥ 1 mol.% a mictomagnetic type order was evidenced.

EPR and magnetic susceptibility studies of manganese ions in Bi2O3GeO2 glasses

Abstract EPR and magnetic susceptibility measurements performed on x MnO · (1 − x )[Bi 2 O 3 ·GeO 2 ] glasses with 0 x ≤ 50 mol.% are reported. The EPR spectra are modified with the increase of manganese ions content. In the concentration range 0 x ≤ 30 mol.% the spectra are characterized by the appearance of two resonance lines at g ≅ 4.3 having a resolved hyperfine structure for 0 x ≤ 1 mol.%, characteristic for isolated Mn 2+ ions in low-symmetric sites and g ≅ 2.0 without hyperfine structure characteristic to clustered Mn 2+ ions. The ΔB values of g ≅ 2.0 resonance lines and magnetic susceptibility data suggest the appearance of superexchange interactions for x ≥ 30 mol.%. From the Curie constant values we have established that in these glasses both Mn 2+ and Mn 3+ ions are present, determining their magnetic behaviour.

EPR and magnetic susceptibility studies of Cu2+ ions in Bi2O3·GeO2 glasses

Abstract Results of EPR and magnetic susceptibility measurements performed on x CuO·(1− x ) [Bi 2 O 3 ·GeO 2 ] glasses with 0 x ≤50 mol % are reported. EPR data suggest a hexacoordinated geometry of the tetragonal-distored octahedral symmetry for Cu 2+ ions. The modification of EPR spectra with the increasing of CuO content are explained supposing that these are the results of a superposition of two EPR absorptions: one is asymmetrical, typical for isolated Cu 2+ ions ( g ‖ ≅2.34 and g ⊥ ≅2.07) and the another a symmetrical line at g ≅2.10, characteristic for clustered ions. The dependence of the g ≅2.10 linewidth vs CuO content shows that between clustered copper ions the dipole-dipole interactions prevail. These data consist with those obtained from magnetic measurements, which indicate that the Cu 2+ ions are magnetically isolated. From the Curie constants it was established that in this glass system the copper ions are in both Cu + and Cu 2+ valence states, the latter being ≈45% of CuO content in all studied glasses.

Electron paramagnetic resonance study of Fe2O3Bi2O3GeO2 glasses

Abstract Homogeneous glasses of the system x Fe 2 O 3· (100 − x )[Bi 2 O 3· GeO 2 ] were obtained within 0 x ⩽ 20 mol%. EPR absorption spectra due to Fe 3+ (3d 5 ) ions show the g ≈ 4.3 line as the main feature. The site symmetry of Fe 3+ paramagnetic ions is predominantly rhombic. Mixed valence states of iron ions in samples with x > 5 mol% Fe 2 O 3 were detected.

EPR and magnetic susceptibility studies of Cr2O3–Bi2O3–GeO2 glasses

Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements have been performed on xCr2O3(1−x)[Bi2O3·GeO2] glasses with 0<x≤20 mol%. These data show that the chromium ions are in Cr3+ valence state and for x≤5 mol% they are isolated or experience dipole–dipole interactions. For higher Cr2O3 content the Cr3+ ions participate to the dipole–dipole and superexchange type interactions.

EPR and magnetic susceptibility studies of Cu2+ ions in TeO2B2O3PbO glasses

Abstract Results of EPR and magnetic measurements performed on x CuO(1− x )[70TeO 2 25B 2 O 3 5PbO] glasses with 0 x ≤40 mol % are reported. The modifications of EPR spectra with the increasing CuO content are explained as the result of the superposition of two EPR absorptions, one showing the hyperfine structure typical for isolated Cu 2+ ions and the other consisting of a broad line centered at g ≅ 2.2 typical for clustered Cu 2+ ions. Beside the dipole-dipole coupling between Cu 2+ ions, the EPR and magnetic data suggested that for x ≥ 20 mol %, negative superexchange interactions appear, too. The values of the EPR parameters and magnetic moments prove that the Cu 2+ ions are situated in axially distorted octahedral vicinities. From the measured Curie constants it was established that in this glass system for x ≥ 20 mol % the copper ions are in Cu 2+ and Cu + valence states. For samples with x ≥ 20 mol %, a downward curvature of the reciprocal susceptibility dependence with temperature was observed at T 2 B 2 O 3 PbO glasses are analyzed in terms of a random distribution of Cu 2+ ions in the glass matrix.

Structural and magnetic properties of MnO-B2O3–SrO glasses

The Mn2+ ion distribution in different structural units in 2B2O3·SrO glasses was revealed by means of electron paramagnetic resonance measurements. Octahedral symmetric sites, tetragonally distorted, were detected and also the progressive clustering of Mn2+ ions above a certain impurity level (x ≥ 10 mol % MnO). Magnetic measurements revealed that both Mn2+ and Mn3+ ionic species are simultaneously present in the matrix and that a transition from magnetically isolated ions to antiferromagnetically coupled pairs occurs on increasing the manganese content over 10 mol % MnO.

Magnetic properties of xMnO · (1 − x)[Bi2O3 · PbO] glasses

Abstract The magnetic susceptibility measurements have been performed on xMnO · (1 − x)[Bi2O3 · PbO] glasses with 0

The valence states and magnetic interactions between manganese ions in TeO2PbOB2O3 glasses

Abstract The temperature dependence of the magnetic susceptibility of x MnO · (1 − x )[70TeO 2 · 25B 2 O 3 · 5PbO] glasses with 0 x ≤ 40 mol% have been investigated. The valence states and the distribution of manganese ions in the glass matrix depend on the concentration of these ions. We have established that in these glasses for x > 10 mol% both, Mn 2+ and Mn 3+ ions are present, which explains their magnetic behaviour.

Magnetic properties of xCr2O3 · (1 − x)[Bi2O3 · PbO] glasses

Abstract EPR and magnetic susceptibility measurements have been performed on x Cr 2 O 3 · (1 − x )[Bi 2 O 3 · PbO] glasses with 0 x ≤ 30 mol%. These data show that the chromium ions are in the Cr 3+ valence state. For x ≤ 5 mol% most of these ions are isolated or experience dipole-dipole interactions, but for higher Cr 2 O 3 concentrations the dominant part of them are magnetically coupled by negative superexchange interactions.