An electron paramagnetic resonance study of Pr0.6Ca0.4MnO3 across the charge-ordering transition

We report the first electron paramagnetic resonance studies of single cryst als and powders of Pr0.6Ca0.4MnO3 in the 300-4.2 K range, covering the char ge-ordering transition (T-CO) at similar to 240 K and antiferromagnetic tra nsition (T-N) at similar to 170 K The asymmetry parameter for the Dysonian single-crystal spectra shows an anomalous increase at T-CO. Below T-CO the g-value increases continuously, suggesting a gradual strengthening of the o rbital ordering. The linewidth undergoes a sudden increase at T-CO and cont inues to increase down to T-N. The intensity increases as the temperature i s decreased until T-CO is reached, due to the renormalization of the magnet ic susceptibility arising from the build-up of ferromagnetic correlations.