Magnetic behavior of a La0.9Ca0.1MnO3 crystal - art. no. 214401

We have studied the magnetic behavior of a single crystal of the underdoped manganite La0.9Ca0.1MnO3, by ac susceptibility measurements and emission M ossbauer spectroscopic studies. We do not find any evidence of the presence of antiferromagnetic species as reported by some groups. The breakdown of the long-range ferromagnetic order occurs only above 0.93T(c). This behavio r is in sharp contrast to that observed for polycrystalline La0.8Ca0.2MnO3 and La0.7Ca0.3MnO3 where the breakdown starts occurring at as low a tempera ture as 0.7T(c). It seems that the local distortions introduced by aliovale nt substitutions lead to enhanced anharmonicity of Mn-O-Mn vibrations and t orsional oscillations between Mn-O octahedra, which in turn induce anomalou s breakdown of long-range order even below T-c. However, we observe strong short range order in magnetic polarons above T-c.