Structure And Magnetic Properties Of Perrovskite Manganite Oxide La0.7Ca0.3Mn1-xCoxO3

Perovskite manganite oxide is a kind of strongly correlated electron materi-als, which performs colossal magnetoresistance (CMR) effect. Extensive theoretical and experimental studies have been investigated for strongly correlated perovskite materials. Most of these studies, such as Mean-field (MF) theory, Double-exchange (DE) interaction, Jahn-Teller (J-T) effect, have left some problems unsolved. In this paper, La0.7Ca0.3Mn1_xCoxO3(x=0,0.1,0.2,0.3) were prepared by the conventional solid-state reaction method, with high purity La2O3(4N), CaO (4N), MnO2(4N) and CoO (4N). And we tried to find the law of crystal structure and magnetic phase transition with changing components of the samples.The X-ray diffraction analysis showed that the samples were single phase with orthorhombic(Pnma) structure. The lattice constants and the unit cell volume de-creased slightly with Co doping. This attributed that the size of Co ion was smaller than that of Mn ion, which distorted the lattice and, decreased of the lattice con-stants and the unit cell volume.The magnetic properties of the specimens were measured via vibrating sample magnetometer (VSM). Critical phenomena were analyzed by the modified Arrot-plot method and the Arrot-Noakes state equation. The calculation indicated that the magnetic entropy change-△S were4.694J·kg-1·K-1,1.403J·kg-1·K-1,1.788J·kg-1·K-1,0.91J·kg-1·K-1, respectively. The ferromagnetic-paramagnetic transi-tion temperature (the curie temperature TC) were:210±4K,155±4K,144±1K, 108±2K, respectively. And the critical exponents (β、γ、δ) were:β=0.211±0.03,0.34±0.02,0.29±0.03; γ=1.133±0.07,1.15±0.16,1.34±0.18; δ=5.917,3.448,5.405, respectively.-△S and TC decreased with the consistence x increase; the β values of x=0.2and0.3were close to3D Ising model; the γ values of x=0.1and0.2were close to3D Ising model, and the Y values of x=0.3was close to3D Heisenberg model; the δ values of x=0.1and x=0.3were close to3D Ising model, and the δ value of x=0.2was close to Mean Field model. On the whole, the critical exponents of our samples were most close to3D Ising model. It meaned that the exchang interaction of magnetic ions was a short range interaction.