Articles written in Proceedings – Section A

• Electron paramagnetic resonance of Mn2+ in NaF single crystals

The electron paramagnetic resonance of Mn2+ in NaF single crystals is investigated at different temperatures from 573° K to 93° K. Four different spectra designated as I, II, III2 and III4 are observed. Spectrum I consists of a single broad resonance corresponding to precipitated Mn2+ ions. Spectrum II is isotropic and centred nearg = 2.00. This spectrum corresponds to substitutional Mn2+ ions with remote charge compensating sites and therefore with local cubic symmetry. Spectrum III2 withg = 2.014 and spectrum III4 withg = 1.995 are also due to substitutional Mn2+ ions but subjected to tetragonal crystalline fields and are the same as those reported by earlier workers. Superhyperfine structure has been observed in spectra II, III2 and III4. The analysis of that structure in spectra II and III2 has been carried out for the first time and the constants As, and Aσ are given. The spectra are analysed by the usual spin-Hamiltonian method.

• Electron paramagnetic resonance studies of VO2+ in single crystals of NaCl, KCl and RbCl

Electron paramagnetic resonance (EPR) of VO2+ radicals incorporated in face-centred single crystals of NaCl, KC1 and RbCl has been studied in the temperature range of 77° K to 330° K. At liquid nitrogen temperature, anisotropic spectra have been recorded in each case while spectra recorded at room and higher temperatures are isotropic suggesting the existence of a fast readjustment of VO2+ molecular ions in the crystals at higher temperature while this motion gets hindered at liquid nitrogen temperatures. Spin-Hamiltonian constants are calculated from the recorded isotropic and anisotropic spectra. The line widths in each case are found to obey a parabolic law originally proposed by Kivelson. The constants which give a close fit have been evaluated. The random orientation and readjustment of V-0 bond in these alkali chloride crystals is explained on the assumption that the medium exhibits a “liquid-like” nature for VO2+ molecular ion as far as the electron paramagnetic resonance absorption is concerned.

• Electron paramagnetic resonance of mn2+ in single crystals of Cesium Sulphate

Electron paramagnetic resonance (EPR) of divalent manganese ion has been studied at 9.5 KMc/sec. These studies reveal that Mn2+ ion substitutes at a β-Cs+ site and gets associated with a vacancy at a neighbouring β-Cs+ site in the aft-plane. Thez-axis of this ββ complex makes an angle of 25° with the crystallographicb-axis. The spectra observed have been described by the spin-Hamiltonian for Mn2+ in rhombic crystalline field. The temperature dependence of the parameters D and E has been studied in the range 293°–77° K. The spectra for the observed complex along its three-principal axes have been analysed using second order perturbation equations. The spin-Hamiltonian parameters obtained from the spectra taken at room temperature are:$$\begin{gathered} g_z = 2 \cdot 000 \pm 0 \cdot 003, g_x = 2 \cdot 015 \pm 0 \cdot 003, g_y = 2 \cdot 000 \pm 0 \cdot 003; \hfill \\ A_z = - 93 \pm 1, A_x = - 91 \pm 1, and A_y = - 91 \pm 1 G; \hfill \\ D = - 941 \pm 3 and E = - 14 \pm 4 G; \hfill \\ b^\circ _4 = \left( {0 \cdot 0} \right), b_4 ^2 = \left( {13} \right), and b_4 ^4 = - 77 \pm 5 G \hfill \\ \end{gathered}$$

•