Study Of Doping And Hysteresis Of Nd_0.7Ca_0.3-xSr_xMnO₃

Electrical transport and magnetic properties of La_0.7Ca_0.3-xSr_xMnO₃ and Nd_0.7Ca_0.3-ySr_yMnO₃ systerm have been investigated. Experimental results show that the two manganites with different A-site ion have obviously different electrical transport properties, which can not be interpreted only on the consideration of the average ionic radius . Together with the different magnetic moments of the two A-site ions, the different electrical transport between the La³⁺ and Nd³⁺ based manganites are discussed , in which the inhomogeneity related to magnetic sublattices of A-site ion has an important effect on the electrical transport properties of manganites. In this thesis, the main investigation including:1. Introduced the research history and the fact application of the magnetoresistance materials. We have summarized the crystal structure, electron structure, magnetic structure, electrical transport and magnetic properties of perovskite manganites, and then described some theoretical work about these materials.2. We introduced the mainly preparation procedures for perovskite manganites, and produced the La_0.7Ca_0.3-xSr_xMnO₃ and Nd_0.7Ca_0.3-ySr_yMnO₃ systerm materials by the solid-state reaction and the sol-gel method .The electrical transport and magnetic properties were measured in liquid nitrogen measurement system and commercial Physical Property Measurement System (Quantum Design PPMS).3. Prepared the La_0.7Ca_0.3-xSr_xMnO₃ systerm materials by the solid-state reaction ,and measured the electrical and magnetic transport properties .4.In the Nd_0.7Ca_0.3-ySr_yMnO₃ systerm ,experimental results showed that the occupation of A sites with ions of significantly different radii was expected to enhance the microstructure inhomogeneity that would play an important role in some processes, such as the spin-lattice and charge-lattice couplings , which was argued to be of special importance in the magnetoresistance effect. 5. In order to compare the electrical properties of the La_0.7Ca_0.3-xSr_xMnO₃ system with the Nd_0.7Ca_0.3-ySr_yMnO₃ systerm , two samples with x,y=0.1 for further investigation was chosen. Some obviously hysteresises were observed in the Nd_0.7Ca_0.3-ySr_yMnO₃ system , and we assumed that the Nd-based manganites f-d exchange coupling seemed to be related to the hysteresises and the enhanced magnetoresistance.