Photoinduced Effect Of Ltmo Film And The Rotating Magnetic Field Of Pb-sn Alloy Solidification Behavior,

The work of the thesis can be divided into two parts:The first part (section 1-3): The CMR and photo-induced effect in the La_1-xTe_xMnO₃(x = 0.01, 0.06, 0.12, 0.18) thin films was investigated .The bulks of nonmetal Te valence magnetite -La_1-xTe_xMnO₃(x = 0.01, 0.06, 0.12, 0.18) were prepared by the solid state reaction . The XRD indicated that the structure of samples is rhombohedra. Then the thin films were prepared by PLD Method.The CMR effect of the thin films was investigated . the films (x=0.06, 0.12, 0.18)show a metal-insulate transition when the temperature raise from 83k to 373K. The temperature of Maximum of resistivity Tp become higher as the increase of the valence x. The transport results show that the data satisfy ρ=ρ₀ +ρ₁T^2.5 for T<0.5T_M1;when T>T_M1 it is agree with polaron model. The samples show CMR effect near Tp.The effect of The continue wave laser (532nm, 40mW) on the film was also investigated. Below T_M1 ,the resistivity increase under photo inducing. The maximum resistivity change(Δρ/ρ₀) in the La_0.82Te_0.18MnO₃ sample can reach 51.1% in 253K which is more large than that of hole-doped manganites. Above T_M1 there is a photoconduction. The relaxation was observed in the experiment of La_0.82Te_0.18MnO₃ film in 248K when the laser turn on and off. The resistivity ρ(t) and time t meet the exponential formula ρ = ρ₀ + A exp(t / τ).The second part (section 4-5): Develop the solidification device under Rotating-magnetic field. The heating temperature can reach 600℃. The intensity of magnetic field is 0.5T. The maximum rotational speed is 1200r/min. The solidification of Pb-Sn alloy under rotating-magnetic field was studied. According to the cooling curves, The roating magnetic field tend to accelerate the cooling rate and stimulate the nucleation of the melt compared to static condition .The stirring effect of magnetic tend to provide some extra energy fluctutation to overcome the thermodynamic barrier for nucleation. It is found that ,for Pb-61.9wt%Sn eutectic alloy,magnetic field induced the forced convection of the melt which result in a microstructure of lamellas �'coarser lamellas�' anomalous eutectic"and suppression of gravity-microsegregatio-n and it was revealed that a "lamellar eutecticanomalous eutectic" .Meanwhile, for Pb-50wt%Sn eutectic alloy, a "dendrite manner spheric grain" microstructre change of the primary phase (Pb) occurs and conspicuous grain refinement effect takes place .These are explained by the forced convection inside the melt.