EPR studies on single crystals of $Pr_{1-x}Pb_xMnO_3$

Electron paramagnetic resonance (EPR) studies are carried out on single crystals of $Pr_{1-x}Pb_xMnO_3$, for x=0.23 and 0.30. The crystal with x=0.23 undergoes a transition from paramagnetic insulator to ferromagnetic insulator with Curie temperature View the MathML source. The crystal with x=0.30 undergoes a transition from paramagnetic insulator to ferromagnetic metal with Tc\sim200K. The EPR analysis is carried out in the paramagnetic region for both the crystals. The EPR signals are fitted to the Dysonian equation. Linewidth, intensity and asymmetry parameters are plotted as a function of temperature down to Tc. The intensity shows a simple Curie-Weiss behaviour. The spin relaxation takes place through a bottleneck mechanism according to which linewidth depends only on strong exchange interaction between $Mn^{3+}$ and $Mn^{4+}$ ions. Around 240 K a secondary low field EPR signal is observed for both compositions which persists till around 200 K indicating a possible phase separation