Preparation And Physical Property Research Of La_1-xBi_xMnO₃ And It's Films

The colossal magnetoresistance(CMR) behaviors in perovskite oxides have attracted great attention due to both fundamental theory of Manganese condensed matter physics and potential applications of CMR materials in magnetic devices,e.g.,read and write heads for magnetic disk drivers,magnetic random access memories as well as magnetic field sensors. Therefore,the study on CMR effect has become a focus of recent condensed physics and material science.In this thesis,the author has investigated the physics and transport properties in bulks and thin films of Bi-doped manganese oxide LaMnO₃.In chapter 1,we detailedly introduced the research process in manganese oxides and physical properties,we discussed some probably theoretical models about CMR in manganese oxides.In chapter 2,the crystal structure,microstructure,and electromagnetic properties of polycrystalline bulk La_1-xBi_xMnO₃(x=0,0.1,0.2,0.3,0.4,0.5)are investigated.X-ray results showed that the structure of these samples has changed from orthorhombic to rhombohedral and to orthorhombic in the process that Bi-doped by a low to high doping.SEM images show when lower-doping the grain boundaries of these samples are clearly visible and the grain size gradually increase as Bi-doping increasing.The samples' infrared absorption spectra found all samples appear the absorption peak at range of 580-606cm^-1 and the peak moves from higher frequency to lower frequency along with the increasing Bi doping.The magnetic properties of these samples were measured at 300 K and 77 K separately.The measuring results show that the magnetoresistance reduced firstly,and then increased With the increasing in the content of Bi-doped.For the same samples,the magnetoresistance at 77 K are larger than at 300 K,and the sample La_1-xBi_xMnO₃(x =0.2) was observed the largest magnetoresistance effect,the magnetoresistance(MR) at 1.5T were observed at 300 K and77 K,and value of MR is 0.34%and 15.67% separately.In Chapter 3,the structure and properties of La_0.8Bi_0.2MnO₃ film are carefully investigated.By using RF magnetron sputtering method prepared thin film on Si[100]substrate and then the films treated at different temperatures,the results of XRD patterns spectra show that the structure of films are rhombohedral structure,annealing temperature increased the intensity of diffraction peaks;the results of AFM show as the annealing temperature rise,the grain size of the films gradually increase and the superficial roughness of the films decrease;the results of XPS show that Mn⁴⁺/Mn³⁺ ratio increases and this promote the double exchange.The measuring results indicate that annealing temperature have a significant impact on the magnetoresistance of the films,as the annealing temperature rise,the magnetoresistance of films increased,the magnetoresistance of the film which are annealed at 850℃were observed at 77 K,magnetic field 1.5 T,and the value reached MR = 26.98%.