Electron paramagnetic resonance study of S− and S− 3

Abstract

Two new sulphur are reported in monocristalline rubidiumchloride doped with rubidium and sulphur, and irradiated with X-rays at room temperature. By an extensive comparison with other experimental data on chalcogen centres in alkali halides an interstitial RbCl:S^? and a substitutional RbCl:S^? ₃ model is proposed for these paramagnetic defects. Theoretical calculations confirm the S^? ion model for the former.     

Electron paramagnetic resonance of Gd3+ in Nd2(SO4)3 · 8H2O single crystal

Electron paramagnetic resonance study has been carried out in Gd3+ doped single crystals of Nd₂(SO₄)₃·8H₂0 at three different temperatures. Two magnetic complexes exhibiting orthorhombic or lower symmetry are found and the results have been fitted to a suitable spin-Hamiltonian. The ten “best fit” parameters are obtained from two computer programs. Zero-field splittings of Gd3+ have been deduced from spin-Hamiltonian parameters and are compared with those observed directly by Bogle and Symmons. Fine forbidden transitions ∥ΔM_s∥ I > 1 are analyzed using numerical solution of the Hamiltonian matrix.     

Electron paramagnetic resonance of the two-dimensional system Mn(CH3COO)2·4H2O

A single crystal Electron Paramagnetic Resonance (EPR) study of manganese acetate tetrahydrate was carried out at Q-band and room temperature. The EPR spectrum always reduces to a Lorentzian singlet with g=2.008. The maximum of linewidth observed along a¹ reveals the spin diffusion effects in this two-dimensional system. The maximum of linewidth observed along b reveals the exchange narrowed dipolar interactions in the linear trimers, as well as the contribution of the fine structure terms.     

Electron paramagnetic resonance and spinlattice relaxation of Cu2+ ions in ZnSeO4·6H2O

In this paper, we present detailed studies of the EPR spectra of Cu²⁺ ions in single crystals of ZnSeO₄·6H₂O. We describe the spectrum with a rhombic spin Hamiltonian with the following parameters: g_z=2.427; g_y=2.095; g_x=2.097; A _z ⁶⁵ =138.4·10^?4 cm^?1; A _x ⁶⁵ =22.3·10^?4 cm^?1. We studied spin-lattice relaxation in the temperature range 4–300 K at the frequency v≈9.3 GHz. The measured spin-lattice relaxation rate for the orientation H∥L₄ is described well at T<5 K by a linear dependence, while at T>5 K it is described by the sum of three exponentials: $$T_1^{ - 1} = 0.27T + 3.3 \cdot 10^{\text{s}} \exp \left( {\frac{{ - 69.5}}{T}} \right) + 2.6 \cdot 10^7 \exp \left( {\frac{{ - 140}}{T}} \right) + 1.36 \cdot 10^{10} \exp \left( {\frac{{ - 735.6}}{T}} \right){\text{ sec}}^{{\text{ - 1}}} $$ .We discuss possible reasons for the exponential dependence of T ₁ ^?1 for the Raman process.     

Electron paramagnetic resonance and photoluminescence properties of α-Al2O3:Cr3+ phosphors

The red emitting Cr³⁺ activated α-Al₂O₃ powder phosphor has been prepared by easy combustion reactions from mixed metal nitrate reactants and urea with ignition temperatures of 500 °C. The as-synthesized powder was characterized by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared techniques. The X-ray diffraction pattern reveals that the phosphor crystallized in the hexagonal α-Al₂O₃ phase directly from the combustion reaction. The EPR spectrum exhibits an intense resonance signal with effective g value at g=3.33 along with a few weak resonance signals with effective g values at g=13.7, 2.34, 1.95, 1.49, and 1.26. The spin concentration (N) and its paramagnetic susceptibility (χ) have been evaluated. The excitation spectrum consists of two broad intense bands at 415 nm and 555 nm and are assigned to ⁴A_2g (F)→⁴T_1g (F) and ⁴A_2g (F)→⁴T_2g (F) transitions, respectively. The intense fluorescence peak around 691 nm is attributed to ²E _g →⁴A_2g transition of Cr³⁺ ion. By correlating EPR and optical data, the crystal field splitting parameter (Dq), Racah inter-electronic repulsion parameter (B) have been evaluated and discussed. The EPR and optical studies reveal that Cr³⁺ ions are occupying in Al³⁺ sites in octahedral coordination.     

Electron paramagnetic resonance of Gd3+ ions in Ca1 − x − y Y x Gd y F2 + x + y crystals

Electron paramagnetic resonance of Ca_{1 ? x ? y} Y _x Gd _y F_{2 + x + y} single crystals has revealed spectra that are not typical of gadolinium-doped CaF₂ crystals. These spectra have a nearly tetragonal symmetry and are most probably caused by Gd³⁺ ions localized in yttrium clusters. Weak spectra of tetragonal Gd³⁺ centers, whose parameters are close to those of a cubic gadolinium center caused by an isolated Gd³⁺ ion, have been also detected. These centers are attributed to isolated Gd³⁺ ions localized near octahedral rare-earth clusters or their associations.     

Giant magnetoresistance in pyrochlore Tl2−xInxMn2O7

We report the giant magnetoresistance (GMR) effect in the first non-perovskite compound Tl₂Mn₂O₇ forming in the pyrochlore structure. Our results, furthermore, show that the GMR is greatly enhanced in the miscibility gap region of the quasi-binary phase of Tl₂Mn₂O₇In₂Mn₂O₇. Our findings should invigorate the exploration of new GMR materials as well as possible utilization of phase mixing to enhance the GMR effect.     

High-field electron paramagnetic resonance study of the polymerization in Na2Rb1−x Cs x C60

We report on the study of the magnetic properties of the low-temperature polymer phases in N₂Rb_1?xCs_xC₆₀ at 110 GHz microwave frequency withx varying between 0 and 1. The magnetic and structural properties of the polymer phase strongly depend on the Cs content and its electronic structure progressively becomes quasi-one-dimensional asx is increased. While the electronic properties of the polymeric Na₂RbC₆₀ appear to be close to three-dimensional metal, Na₂Rb_0.3Cs_0.7C₆₀ shows characteristics of quasi-one-dimensional metal where instability in the electronic structure was found as detected by the sudden disappearance of the ESR intensity due to the opening of the gap at the Fermi surface. The observation of an additional resonance line below 15 K, which could be attributed to antiferromagnetic resonance, suggests that the low-temperature polymeric phase in Na₂Rb_0.3Cs_0.7C₆₀ has a well-defined magnetic ground state.     

Proton nuclear magnetic resonance in paramagnetic NiSO4 · 1 H2O

Parameters characterizing the magnetic interactions between the paramagnetic ions Ni²⁺ and the protons of crystalline water in powderedNiSO ₄ · 1H ₂O were derived from the field and temperature dependences of the second moment of NMR spectra. The Curie-Weiss constant, magnetic moment _i and the part of second momentM ₂O corresponding to the nuclear dipoledipole interaction were evaluated from the experimental data. The parameters characterizing the local magnetic field acting on the proton-pairs were calculated and compared with those obtained from the analysis of the shape of the NMR spectrum.The authors express their grateful acknowledgement to Prof. Dr. hab. Z. Pajak, Dr. S. GIo-winkowski, Dr. J. Kapturczak and Ing. W. Porzuckoviak from Institute of Physics, A. Mickiewicz University in Poland for their help in NMR measurements and fruitful discussions.     

Specific Heat of the Er2Ge2O7–Er2Sn2O7 Solid Solutions in the Temperature Range of 350–1000 K

Physics of the Solid State - Er2Ge2O7–Er2Sn2O7 solid solutions have been obtained using solid-state synthesis by burning the stoichiometric mixtures of the initial oxides in air in the...     

Electron paramagnetic resonance of quasi-one-dimensional crystal [Nd2(Cl3COO)6(H2O)3]n · nH2O

A quasi-one-dimensional single crystal of [Nd₂(Cl₃COO)₆(H₂O)₃]_n · nH₂O in which chains are built up of two alternating neodymium-ion dimer fragments is studied by the EPR technique. It is found that anisotropic interactions between neodymium ions in a chain are responsible for the complex shape of the EPR spectrum. Two groups of EPR signals are distinguished in the spectrum. Each group corresponds to one of the chain dimers disturbed by the interaction with neighbors in the chain. The shape of the EPR spectra is interpreted as a superposition of the spectra of chain fragments which have different lengths and are formed by the alternating magnetic triplet and nonmagnetic singlet states in the chain. Consideration is given to two cases when two alternating dimer fragments are either equivalent or nonequivalent to each other. It is shown that the spectral shape is primarily determined by the superposition of the spectra of an isolated triplet state (S=1), two interacting triplet states, and three interacting triplet states whose weighting contributions differ for the above two cases. The tensors of the anisotropic spin-spin interaction are determined, and the contribution from the isotropic component of the interaction is estimated.     

Electron paramagnetic resonance of globin proteins – a successful match between spectroscopic development and protein research

At the start of the twenty-first century, the research into the haem-containing globins got a considerable impetus with the discovery of three new mammalian globins: neuroglobin, cytoglobin and androglobin. Globins are by now found in all kingdoms of life and, in many cases, their functions are still under debate. This revival in globin research increased the demand for adequate physico-chemical research tools to determine the structure-function relationships of these proteins. From early days onwards, electron paramagnetic resonance (EPR) has been used in globin research. In recent decades, the field of EPR has been revolutionised with the introduction of many new pulsed and high-field EPR techniques. In this review, we highlight how EPR has become an essential tool in globin research, and how globins equally provide ideal model systems to push technical developments in EPR.     

Electron–Hole Dimers in the Parent Phase of Quasi–2D Cuprates

Physics of the Solid State - The key feature of parent cuprates of the La2CuO4 type, in addition to their high ionic polarizability and closeness to polarization catastrophe, is identified as their...     

Electron–Phonon Renormalization of the Electron Mass in a Metal beyond the Adiabatic Approximation

Journal of Experimental and Theoretical Physics - We analyze the renormalization of the electron mass due to the electron–phonon interaction and interaction constant λ associated with...