The Transport Properties And Martensitic-like Transitions In The Perovskite Manganites

Because of the large MR effect, the perovskite manganites exhibit potential applications in the field of magnetic random access memories, magnetic refrigeration and so on. Meanwhile, this compound is one of the typical strongly correlated electron systems. The interplay between charges, spin, phononic, and orbital degrees of freedom gives rise to several novel properties, such as metal-insulator transition, charge ordering, obital ordering, phase separation and so on. In condensed matter physics, the compound has been referred as a nature lab because of its rich physics. In this thesis, we investigate the electrical transport and magnetic properties of (La1-xBix)2/3Ca1/3MnO3 and the martensitic-like effect in the A-site and B-site doped maganites.The thesis is divided into six chapters.In chapter one, we present a brief introduction of the physical properties of the perovskite manganites, including the crystal structure, magnetic property and electronic configuration of the manganites. The electrical transport and magnetic properties of the compound in the paramagnetic and ferromagnetic state are discussed, respectively. Some physical concepts, including charge-spin-orbital ordering, phase separation, and their relations with CMR effect are interpreted. Finally, we discussed the main mechanism in the CMR effect.In chapter two, we give a general introduction of the electrical transport and magnetization measuring system in the pulsed high magnetic field. In this chapter, the priciple of the two measuring systems are presented in detail. In the electrical transpot measuring system, the digital lock-in technology is highlighted. The fabrication of the pick-up coils and the related circuit are discussed in the magnetization system.In chapter three, the electrical transport and magnetic properties of (La0.9Bi0.1)2/3Ca1/3MnO3 and (La0.75Bi0.25)2/3Ca1/3MnO3 are investigated in the pulsed high magnetic field. In order to describe the magnetotransport properties of (La0.9Bi0.1)2/3Ca1/3MnO3, a spin-dependent hopping model was employed. The results of the magnetization measurement of (La0.75Bi0.25)2/3Ca1/3MnO3 demonstrate that a magnetic field of 23T could destroy the charge ordering phase completely. In chapter four, the nonlinear behavior of (La0.73Bi0.27)2/3Ca1/3MnO3 is discussed. The I-V curves are measured under different temperatures and different magnetic fields. The results prove that the Joule-heating effect is the main reason in the nonlinear behavior of (La0.73Bi0.27)2/3Ca1/3MnO3.In chapter five, the electrical transport and magnetic properties of Pr0.5Ca0.5Mn0.97Ga0.03O3 were invesitigated. Two distinct metamagnetic transitions are observed with a slow field sweep rate. We propose that the conventionally observed magnetic steps correspond to the pseudo-CE-type AFM-FM transition. The H-T phase diagram of the sample is constructed finally.In chapter six, we investigate the electrical transport and magnetic properties of (La0.73Bi0.27)2/3Ca1/3MnO3. Our experiment demonstrate that the critical field keep constant under different field sweep rates, which demonstrate that the martensitic effect could not describe well in this sample. An antiferromagnetic cluster model was assumed to explain the sharp steps in the compound.