Emission Mِssbauer studies of the magnetoresistive compound, La0.7Sr0.3MnO3

The magnetic behavior of the Sr0.3 manganite is studied using a local microprobe, 57Co. In contrast with Ca substituted manganites, a much larger fraction of the material exhibits short-range order with superparamagnetic-like behavior even at 80 K. The differences in behavior are attributed to the large mismatch between the ionic radii of La+3 and the divalent substituent Sr+2, which introduces anharmonicity in local vibrations. In common with all other compounds exhibiting negative bulk magnetoresistivity, the Sr0.3 compound also exhibits very marked softening of lattice as one approaches Tc from below. Application of an external magnetic field results in coalescing of nanosized magnetic clusters to form larger ones with better alignment of spins.