Multifrequency electron spin resonance study of the charge-ordered manganite Nd0.5Ca0.5MnO3

We performed multifrequency electron spin resonance (ESR) on the antiferromagnetic (T-N = 160 K) and charge-ordered (T-CO = 250 K) insulating manganite Nd0.5Ca0.5MnO3. Temperature (4-300 K) and frequency (9.4-285 GHz) dependence of the linewidth, intensity and position of the ESR line were studied. In the paramagnetic state we observe a single Lorentzian absorption line. For a given frequency, the ESR line position is temperature independent (close to g = 1.99). A strong linewidth broadening is observed below T-CO. This indicates that there is no magnetic order in the temperature range T-CO > T > T-N but strong antiferromagnetic fluctuations are present. Below T-N, due to high-frequency and high-field ESR (up to 12 T) measurements, we were able to observe unexpected lines within the antiferromagnetic gap revealing the presence of a phase separation.