Magnetic properties of colossal magnetoresistive manganese oxides

Abstract

The effects of isovalent substitution into the lanthanide sites in La1−xYxCa0.30MnO3−δ 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 smaller lanthanide Y is introduced into the lattice. We will provide evidence that a key signature of the magnetic properties of these oxides is the presence of an unusual long tail in the magnetization versus temperature curves M(T), extending up to 3TM 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 Mössbauer 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.