THE TEMPERATURE-DEPENDENCE OF THE SPIN-HAMILTONIAN PARAMETERS FOR MN2+ IMPURITY IONS IN CALCITE AND COAL

The temperature dependences of the spin-Hamiltonian parameters have be en determined in the temperature interval from 286 to 673 K for Mn2+ i mpurity ions in polycrystalline calcite samples from the EPR spectral perpendicular and parallel components using a computer-simulation best -fit procedure. The temperature dependences of the spin-Hamiltonian pe rpendicular-component parameters for Mn2+ impurity ions in a coal have also been determined. In calcite, the temperature dependences of the spin-Hamiltonian parameters (c(0)(2))(parallel to), (c(0)(2))(perpendi cular to), and A(perpendicular to) agree with those obtained in a prev ious study on a monocrystalline sample when the external magnetic fiel d was parallel to the [1 1 1] direction. The values of (c(0)(4))(perpe ndicular to) obtained in this study differ from those reported previou sly by similar to 10% although both have a similar temperature depende nce. However, both \(c(0)(4))(perpendicular to)\ and \(c(0)(4))(parall el to)\ increase unexpectedly at temperatures above 630 and 570 K, res pectively. A small and linear increase in g(perpendicular to) by simil ar to 0.00009 (2) was observed. The temperature dependences of the spi n-Hamiltonian parameters obtained from the parallel components differs from that obtained from the perpendicular components. The values of ( c(0)(2))(parallel to) and (c(0)(2))(perpendicular to) are in much bett er agreement than those for the other spin-Hamiltonian parameters; g(T )(parallel to), A(T)(parallel to), and (c(0)(4))(parallel to) have tem perature dependences which cannot be explained by existing theory. The temperature dependences of c(0)(2) and A for the coal sample, agree w ith those for calcite within 0.5 and 0.05%, respectively. However, the Delta g temperature dependences in calcite and coal differ significan tly, because of errors caused by the greater lineshape broadening obse rved in coal. The agreement of the temperature dependences of Mn2+ spi n-Hamiltonian-parameter values in calcite and the coal sample confirms the conclusion that the Mn2+ spectrum in coal originates from its cal cite mineral component. (C) 1994 Academic Press, Inc.