Paramagnetic-ferromagnetic and insulator-metal phase transitions in La^sub 0.88^MnO^sub 2.95^

Abstract

We present the results a study of structure by neutron diffraction and data on the magnetic properties (linear and nonlinear (second and third order) susceptibilities) of polycrystalline La_0.88MnO_2.95. This compound exhibits an insulator-metal (IM) phase transition at T _IM [asymp] 253 K (above the Curie temperature, T _C [asymp] 244 K) and reveals colossal magnetoresistance. The crystal structure is found to be rhombohedral, and the space group is R3c. Analysis of magnetic properties shows that at T* [asymp] 258 K > T _C, isolated paramagnetic clusters occur in the paramagnetic matrix; their concentration increases upon cooling. We observed no noticeable differences between the temperature evolution of the clustered state of this manganite with its insulator-metal transition and in the insulator La_0.88MnO_2.91. Possible scenarios of the paramagnet-ferromagnet and I-M transitions in a self-organized clustered structure are discussed.