Madhusudan K. Bhide

E.p.r. studies on dichloromono(1-phenylamidino-o-alkylurea)copper(II) complexes. Evidence for field induced partial ordering in the solid state and some unusual features in solution

E.p.r. and optical absorption studies have been conducted on dichloromono(1-phenylamidino-o-alkylurea)copper(II) complexes (Alkyl = Me, Et, Pr, Bu or Pe). The e.p.r. spectra of solids, recorded at 300 K, confirmed the square-planar geometry with the unpaired electron in the dx2−y2 orbital of copper. Magnetic field-induced partial molecular alignment has been observed in some of the polycrystalline samples when cooled in a magnetic field of 1 T at 77 K. E.p.r. spectra at 77 K in pyridine and DMF has shown axial ligation of solvent molecules (pyridine and DMF), whereas in MeOH and DMSO at least three structurally different CuII species have been identified. These features are consistent with differences in electronic absorption spectra in the powder and in solution.

EPR studies on (NBu4)2Co2[Cu(opba)]3·S, where opba=ortho-phenylenebis(oxamato) and S=Solvent: unusual case of long-range magnetic order in weakly interacting systems

Abstract Electron paramagnetic resonance (EPR) investigations were carried out on two bimetallic molecular magnets (NBu 4 ) 2 Co 2 [Cu(opba)] 3 ·S, where S=3DMSO·3H 2 O and 2H 2 O, known to exhibit long-range magnetic order below 32 and 34 K, respectively, in the temperature range 300–15 K. Temperature dependence of the intensity of the EPR signal arising from Cu 2+ in these compounds showed a rapid decrease in intensity upon cooling below 65 K, which was accompanied by a disappearance of the super-hyperfine structures, observed on the Cu 2+ signal at higher temperatures, pointing to a Co 2+ Cu 2+ spin–spin interaction following the slowing down of Co 2+ spin–lattice relaxation. The appearance of a new signal at zero field (ZFS) below 40 K is attributed to the onset of long-range magnetic ordering in both the compounds.

Magnetic field dependent microwave absorption studies on a MgB2 superconductor

Polycrystalline MgB2, synthesized using a conventional solid-state reaction route, has been investigated for its magnetic field dependent microwave absorption using a standard X-band EPR spectrometer. The changes in microwave absorption as a function of temperature and/or magnetic field were recorded by following the microwave reflectivity of a sample-loaded cavity. The modulated low-field microwave absorption signal was found to be similar to that observed in high-temperature superconducting materials. The field dependent direct microwave absorption in the 0-10 kG range was used to determine Hc1 values at different temperatures, and the value of Hc1(0) was found to be 250 G. The absorbed microwave power has been found to obey a (H)1/2 dependence with a change of slope indicating a transition from a strongly pinned flux lattice to the flux flow regime.

Nanorods of white light emitting Sr2SiO4:Eu2+: microemulsion-based synthesis, EPR, photoluminescence, and thermoluminescence studies

White light emitting Sr2SiO4:Eu2+ nanoparticles were prepared using reverse micellar route using Tergitol as a surfactant. The systems were characterised by X-ray diffraction, scanning electron microscopy (SEM), photoluminescence, thermoluminescence (TL), and electron paramagnetic resonance (EPR) spectroscopy. SEM shows the formation of silicate nanorods. Two emission bands of bluish-green at 490 nm (S(I)) and of orange-red at 605 nm (S(II)) were observed. The two emission bands are assigned to the 4f–5d transition of Eu2+ ions in two different cation sites in α′-Sr2SiO4 orthorhombic lattices. Gamma-irradiated Sr2SiO4:Eu showed the presence of three TL glow peaks at 437, 487 K and weak peak at 540 K; however, no glow was observed in the undoped sample. Reduction of Eu3+ to Eu2+ is confirmed by EPR spectroscopy.

EPR and ENDOR studies of self(α)-irradiation effects in Pu(VI) oxalate: evidence for participation of 5f electrons of 239Pu in chemical bonding with CO2−

Abstract EPR and ENDOR investigations have been carried out on polycrystalline samples of self( α )-irradiated PuO 2 C 2 O 4 ·3H 2 O (cumulative dose = 1 MGy). The 239 Pu ( I =1/2) hyperfine structure on the EPR signal of the CO 2 − radical ion has given clear evidence for participation of 5f electrons of 239 Pu in chemical bonding. The ENDOR spectra were used to identify unambiguously the hyperfine interaction between the unpaired electron on the CO 2 − radical ion and the nuclear spin of 239 Pu. In addition to the CO 2 − radical ion, EPR evidence was also obtained for the formation of O 2 − during the autoradiolysis of PuO 2 C 2 O 4 ·3H 2 O.