B.P. Maurya

EPR observation of Cu2+Cu2+ pairs in cupric oxide powders

Abstract We report the observation of an EPR spectrum attributable to Cu2+Cu2+ pairs with resultant electronic spin S = 1, from cupric oxide annealed in the temperature range from 700 to 900°C. The spectrum consists of only a single line at g = 3.12 with seven hyperfine components. From the weight loss and oxygen content measurements, it was found that the observation of such a signal strongly depends on the oxygen content of the sample.

Copper tetramers in high-temperature superconductors

Abstract Clusters of four copper ions coupled by an exchange interaction are shown by EPR in the constituents of high- T c superconductors and in an oxygen deficient 123-superconductor. The spin-Hamiltonian parameters of the EPR spectra have been reported. Copper tetramers may be at the heart of the superconductivity mechanism.

EPR and optical studies of VO2+ ions in sodium formate single crystal

Abstract Results of EPR and optical studies of vanadyl ion (VO2+) doped in single crystals of sodium formate are reported. Impurity sites in the unit cell and the molecular structure of the vanadyl complexes are discussed. The spin Hamiltonian parameters are determined. From optical and EPR data, crystal field parameters are calculated and discussed. Two complexes at substitutional sites at two different levels of doping have been identified.

EPR and optical absorption studies of VO2+ and Cu2+ ions doped in LiHSO4 single crystals

Abstract Electron paramagnetic resonance and optical absorption studies of LiHSO 4 single crystal doped with VO 2+ and Cu 2+ have been carried out at room temperature. Two magnetically equivalent but differently oriented VO 2+ complexes are found and molecular bonding coefficients ( β 2 , ϵ 2 ), Fermi contact term ( k ) and dipolar hyperfine coupling parameter (ϱ) are reported. Some interesting but unusual results are obtained in the EPR and optical absorption studies of the Cu 2− ion doped LiHSO 4 .

EPR study of Cu2+ ion doped in potassium oxalate monoperhydrate single crystal

Abstract The EPR study of Cu 2+ doped potassium oxalate monoperhydrate is carried out at room temperature. Two magnetically inequivalent interstitial sites are found embedded in orthorhombic crystal fields. The ground state wave functions are constructed. The obtained results are compared with that of isotypic crystal Cu 2+ doped potassium oxalate monohydrate to explore the difference arising due to the presence of H 2 O 2 in the former and H 2 O in the latter crystal. The spin-Hamiltonian parameters (g- and A-values) covalency parameter (α′ 2 ), the mixing coefficients (α, β) and Fermi contact term ( k ) are calculated for both the complexes.

ESR STUDY OF CuO BULK POWDER AND THIN FILMS

A systematic Electron Spin Resonance investigation is carried out in CuO bulk powder and thin films, after calcining them to different temperatures ranging from 100°C to 1000°C. In CuO powder, two separate signals (one broad and one sharp) were observed at calcination temperature of 500°C, for the fist time. They got intensified, came closer and amalgamated on further heating upto 800°C, indicating complete destruction of antiferromagnetic ordering in this powdered compound. In thin films of CuO, the first appearance of the signal at 200°C and its intensification and shifting on further heating indicates that in thin film form, the destruction of antiferromagnetism takes place much earlier.

S = 12, S = 1 and S = 2 EPR spectra in copper doped KHSO4 single crystal

Abstract In the room temperature EPR investigation of copper doped KHSO 4 single crystals, different signals corresponding to monomer, dimer and tetramer of copper are obtained simultaneously. The spin-Hamiltonian parameters are reported.

Electron paramagnetic resonance and superposition model investigations of Mn2+ ion doped in sodium formate single crystal

Abstract Electron paramagnetic resonance and superposition model analyses of Mn 2+ ion doped in a sodium formate single crystal have been carried out at room temperture. Two types of Mn 2+ complexes were obtained. These complexes are magnetically equivalent but oriented differently. One Mn 2+ ion replaces one Na + ion and ejects one neighbouring Na + ion for charge compensation. The Z -axis of each complex is directed along the Na + Na + (vacancy) direction and the X and Y components along Na + -oxygen directions. By replacement of Na + by Mn 2+ , much local rearrangement takes place. The superposition model anlaysis supports these relaxation effects.

EPR study of Mn2+ ion doped in potassium oxalate monoperhydrate single crystal

Abstract An EPR study of Mn 2+ ion-doped potassium oxalate monoperhydrate single crystal has been carried out at room temperature. Two magnetically equivalent but differently oriented interstitial sites have been found for the Mn 2+ dopants. The spin-Hamiltonian Hamameters are found to be g x = g y = 2.0010, g z = 2.0015; b 2 0 = −440, b 2 2 = 150, b 4 0 = 0.1959; A x = A y = 97.5, A z = 98.5 × 10 −4 cm −1 and polar angles θ = 25° and φ = 30°. The results obtained are compared with those of the isotypic crystal Mn 2+ ion-doped potassium oxalate monohydrate to assess the difference arising from the presence of H 2 O 2 in the former and H 2 O in the latter. Superposition model analysis of zero field splitting for Mn 2+ ion-doped potassium oxalate monoperhydrate single crystal has been carried out.

An EPR study of manganese(II) complexes in potassium chromate single crystal

Electron paramagnetic resonance study of Mn2+-doped K2CrO4 single crystals at room temperature and liquid nitrogen temperature revealed the presence of two pairs of inequivalent Mn2+ complexes. It is concluded that Mn2+ ions are incorporated in the host substitutionally at potassium sites, and an equal number of K+ vacancies are created for charge compensation. The spin—Hamiltonian parameters are evaluated. The principal directions of the crystalline field experienced by the manganese (II) ion are determined and they are found to be consistent with the electrostatic considerations. The hyperfine parameters indicate the significant extent of covalent bonding of ligands with the metal ion.