Covalent Spin Research Articles

ENDOR measurements of spin transfer in (VF6)4-

EPR and ENDOR measurements have been made to investigate the covalent spin transfer for substitutional V2+ in KMgF3. The hyperfine parameters for the F- ligands are A=-20.99+or-0.02 MHz and B=-5.70+or-0.04 MHz. Hence, the unpaired spin densities in fluorine 2ppi , 2psigma and 2s orbits which arise from covalent transfer to, and overlap with, the V2+3d and 4s orbits are estimated to be fpi =(2.6+or-0.3)%, f'sigma =-(0.3+or-0.2)% and f's=-(0.1+or-0.01) respectively. The covalency model used in interpreting the hyperfine parameters leads to a g factor consistent with the experimental value of 1.972.

Exchange interactions between V2+ions in magnesium oxide

The exchange interaction between pairs of V2+ ions occupying substitutional cation sites in magnesium oxide has been studied by electron paramagnetic resonance. For next nearest neighbour pairs coupled via an intervening oxygen ion, transitions within the total spin state S=2 only are observed. Transitions within the S=1 and S=3 levels are broadened by interactions which leave the S=2 level unaffected. The exchange-induced fine structure splitting, De, is almost a factor of two larger than the dipolar term Dd. Although lattice distortion, covalent spin transfer to the ligands and anisotropic exchange interactions may contribute to this discrepancy a significant part must come from so far undetermined mechanisms. The nearest neighbour pairs, which are at right angles with respect to an intervening anion, have been studied in less detail. The interaction is found to be ferromagnetic with J=-7.5+or-3 cm-1.

A spin label study of the recombined lipid and apoprotein of human ertthrocyte membranes

Covalent spin labels and spin probes have been used to study the binding between sialic-acid free (s.a.f.) apoprotein and total lipid of human erythrocyte membranes during the formation of a lipoprotein complex. The data confirm that both electrostatic and apolar interactions are involved in the recombination.

Covalency, Spin Densities, and Neutron Magnetic Scattering

Effects of covalent spin densities on the neutron magnetic scattering are described using results of UHF-MO-SCF calculations for the (MnF6)4− cluster and for a model three-atom system (Sc2+–F−–Sc2+) in a linear configuration. Full variational freedom was given to all the electrons and all multicenter integrals were included. From the computed spin densities magnetic form factors were calculated including nonspherical terms and core polarization effects. Both ferromagnetic and antiferromagnetic states of the three-atom system were studied in order to investigate possible differences in covalent behavior and the contribution of covalency to measurements of zero-point spin deviation.

Configurational entropy of electrons in semiconductors

Abstract All intrinsic semi-conducting elements at absolute zero of temperature have their valence electrons occupying completely the valence band, the electrons being localized as co-valent spin pairs. At non-zero temperature, a fraction of these pairs gets broken, with the corresponding electrons thermally excited into the conduction band. The conduction electrons can be considered ‘non-localized’ and the process of spin decoupling, one of configurational entropy gain for the whole system. On considering the electronic wave function as mixed in character due to electrons ‘localized’ and ‘non-localized’, one can write it as a superposition of a metallic and a cevalent wave function. The resultant Hamiltonian permits one to calculate the configurational entropy of electrons in semiconducting elements and some semiconducting compounds. It is this contribution which is shown to be the reason of excess entropy of fusion of all semiconductor elements. The analysis elucidates some of the anomalous electronic b...

Measurement of the Covalent Spin Distribution in Manganous Fluoride Using Polarized Neutrons

The spatial distribution of the covalent spin density in MnF2 has been obtained from a measurement of the ``forbidden'' magnetic scattering in the nuclear reflections using polarized neutrons. A partial Fourier map of the projected covalent spin on the basal plane was prepared. A model representing the covalent spin by isolated spherical charges that is consistent with the experimental data indicates that the covalent spin density for a single bond undergoes a change in sign as we proceed from the Mn2+ to the F− ion. That part closest to the 3d unpaired electrons carries the same sign as the magnetic ion. The results are discussed in terms of the existing theory.