MAGNETIC-PROPERTIES OF COLOSSAL MAGNETORESISTIVE MANGANESE OXIDES

The effects of isovalent substitution into the lanthanide sites in La1 -xYxCa0.30MnO3-delta oxides is presented. We report on the electrical and magnetic properties of these materials for x=0-0.25. We have found that the ferromagnetic ordering temperature decreases and the cusp of the resistivity occurring at this temperature increases when the smal ler lanthanide Y is introduced into the lattice. We will provide evide nce that a key signature of the magnetic properties of these oxides is the presence of an unusual long tail in the magnetization versus temp erature curves M(T), extending up to 3 T-M and which is very sensitive to the applied magnetic field and becomes increasingly important with the concentration of Y in the lattice. These features signal a strong polarizability of the spin clouds in these materials as our Mossbauer experiments will clearly demonstrate. Finally, we will show that the magnetoresistance of these compounds can be well-described in terms of a spin-disorder scattering mechanism. (C) 1996 American Institute of Physics.