Chongyang Yin

Investigation of A-site La substituted BaTi0.96Mn0.04O3 ceramics: Searching for ferromagnetic origin

Ba1-xLaxTi0.96Mn0.04O3 ceramics (x = 0, 3%, 7%) were prepared by a modified Pechini method and the structure, morphology, magnetic and electric properties have been investigated. X-ray diffraction analysis reveals La3+ ions could suppress the formation of hexagonal phase effectively. The cell parameter c decreases firstly and then increases with the increase of La content, which indicates that La ions have been incorporated into the lattice of BaTi0.96Mn0.04O3, and that Mn ions transform from high valence to low valence. The magnetization, polarization and leakage currents are also influenced by La doping greatly. Detailed analysis of magnetic variation with structural change attributes the room temperature ferromagnetism to double exchange interactions between Mn3+ and Mn4+ ions.

Unusual magnetic transition near metal-insulator transition and paramagnetic anomaly in VO2

Experiments for vanadium dioxide show a magnetic transition characterized by a sharp variation in susceptibility associated with the metal-insulator transition at the temperature Tc. The sample is shown to be of Pauli paramagnetism above Tc but of anomalous paramagnetism below Tc. Considering co-contributions of Pauli paramagnetism of residual V4+ ions and Curie-like paramagnetism of V-V dimers, we propose a phenomenological expression for the temperature-dependent susceptibility below Tc, which yields an excellent agreement with the experimental data. The unusual temperature dependence of Curie-like susceptibility below Tc is explained to be due to the fact that every dimer is formed by spin paring at an angle θ close to 180° and hence has an effective spin expressed as S e f f = cos ( θ / 2 ) which decreases with lowering temperature. The observed metal-insulator and magnetic transitions are argued to be due to a transition from the high-temperature Pauli paramagnetic state of V4+ ions to the low-temper...