An electron paramagnetic resonance study of electron-hole asymmetry in charge ordered Pr1-xCaxMnO3 (x=0.64,0.36)

We present and compare the results of temperature-dependent electron paramagnetic resonance (EPR) studies on Pr1-xCaxMnO3 for x = 0.64, which is electron-doped, with results of studies on the hole-doped, x = 0.36 composition. The temperature dependence of the various parameters obtained from the powder and single crystal spectra show significant differences between the two manganites. At room temperature the 'g' parameter for the electron-doped system is less than the free electron 'g' value 'g(e)', whereas for the hole-doped system it is more than 'g(e)'. Further, the linewidth obtained from the powder spectra as well as the single crystal spectra show different functional dependences on temperature in the two systems. Quite strikingly, the peak observed at T-co in the temperature dependence of the asymmetry parameter, alpha, of the single crystal spectra in the hole-doped system, is absent in the electron-doped system. We understand this contrasting behaviour of the EPR parameters in the two systems in terms of the very different nature of microscopic interactions in them.