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

We report the first electron paramagnetic resonance studies of single crystals and powders of Pr0.6Ca0.4MnO3 in the 300-4.2 K range, covering the charge-ordering transition (T-CO) at similar to 240 K and antiferromagnetic transition (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 orbital ordering. The linewidth undergoes a sudden increase at T-CO and continues to increase down to T-N. The intensity increases as the temperature is decreased until T-CO is reached, due to the renormalization of the magnetic susceptibility arising from the build-up of ferromagnetic correlations.