Electron spin resonance and longitudinal relaxation around phase transition in La0.9Ca0.1 MnO3

With original modulation technique, the longitudinal electron spin-relaxation timeT1 has been measured in the La1-xCaxMnO3 manganite (x = 0.1) both in the paramagnetic state and around the temperature (Tc) of the ferromagnetic ordering. The data are compared with the evolution of the transverse relaxation time T2 as determined from the electron spin resonance (ESR) linewidth. Well above Tc, theT1 =T2 equality was confirmed, whereas a steep slowing down ofT2 was observed asTc was approached (theT1/T2 ratio increased by two orders of magnitude). The temperature dependence ofT1 within the whole temperature range was found to be consistent with that ofT · χ(T), where χ(T) is the electron-spin susceptibility obtained from the ESR absorption area. The interpretation suggests that both the longitudinal and transverse electron-spin relaxation rates are governed by strong exchange interaction between the Mn ions, the ESR linewidth being inhomogeneously broadened in the vicinity of the phase transition.