Critical slowing down of longitudinal spin relaxation in La1-xCaxMnO3 - art. no. 092405

Using original modulation technique, the longitudinal electron spin-relaxat ion time T-1 has been measured directly in the paramagnetic state of three La1-xCaxMnO3 samples (x = 0.2, 0.25, and 0.33). Well above the phase-transi tion temperature T-c, the longitudinal relaxation times are found to be equ al to the transversal ones (T-2) as determined from the electron-paramagnet ic-resonance (EPR) linewidth. whereas a steep slowing down of T-1 with a cr itical exponent alpha similar or equal to 0.5 was observed as T-c was appro ached in all the materials. Various models are discussed, including extreme ly slow internal dynamics, formation of magnetic clusters, and inhomogeneou s EPR broadening near T-c.