We have studied the magnetic behavior of a single crystal of the underdoped manganite La0.9Ca0.1MnO3, by ac susceptibility measurements and emission Mössbauer 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 0.93Tc. This behavior 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 temperature as 0.7Tc. It seems that the local distortions introduced by aliovalent substitutions lead to enhanced anharmonicity of Mn-O-Mn vibrations and torsional oscillations between Mn-O octahedra, which in turn induce anomalous breakdown of long-range order even below Tc. However, we observe strong short range order in magnetic polarons above Tc.
Physical Review B
- Pub Date:
- June 2001
- Electronic and magnetic properties of clusters;
- Solubility segregation and mixing;
- phase separation;
- Hyperfine interactions and isotope effects Jahn-Teller effect