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 at ∼ 240 K and antiferromagnetic transition (TN ) at ∼ 170 K. The asymmetry parameter for the Dysonian single crystal spectra shows anomalous increase at Tco. Below Tco the g-value increases continuously, suggesting a gradual strengthening of orbital ordering. The linewidth undergoes a sudden increase at Tco and continues to increase down to TN . The intensity increases as the temperature is decreased till Tco due to the renormalization of magnetic susceptibility arising from the build up of ferromagnetic correlations. The value of the exchange constant, J , is estimated to