Abstract
In this study, the polycrystalline bulk samples of La1-x PbxMnO3(x=0.1、0.2、0.3、0.4), Pr1-x PbxMnO3 ( x=0.1、0.2、0.3、0.4、0.5), La1-xBaxMnO3(x=0.1、0.2、0.3、0.4) were prepared by traditional powder metallurgy solid-state reaction. Thin films of La0.7Ba0.3MnO3 were grown on SiO2/Si(100) substrate by RF magnetron sputtering to grow [00l] preferred orientation of La0.7Ba0.3MnO3 film. The La1-x PbxMnO3(x=0.1、0.2、0.3、0.4) samples were prepared by two stage calcination, and sintered at 850℃ for 52 hrs. The La1-x PbxMnO3 samples (x≦0.3) belong to rhombohedral structure that is a kind of distorted perovskite structure. The second phase Pb3 Mn6O13 segregates from x=0.4 samples. La0.7Pb0.3MnO3 has an MR value of 7% at room temperature under the applied field i1 Tesla. The Pr1-x PbxMnO3 ( x=0.1、0.2、0.3、0.4、0.5), samples were prepared similarly to La1-x PbxMnO3. Pr1-x PbxMnO3 samples ( x≦0.3) have a distorted perovskite structure. The second phase Pb3 Mn6O13 segregates from x≧0.4 samples too. The Curie temperature of Pr1-x PbxMnO3 was 159.23K, 201.6K, 232.7K, for x=0.1、0.2、0.3 respectively. When the Pb content increases, the MR% ratio increases and the temperature of maximum MR% increase, too. The La1-xBaxMnO3 .( x=0.1, 0.2, 0.3, 0.4 ) samples were prepared by one-step calcined and sintered at 1400℃ for 4 hours. The structure of La1-xBaxMnO3 .( x=0.1, 0.2, 0.3, 0.4 ) is the same as that of La1-x PbxMnO3. One of La1-xBaxMnO3, the La0.7Ba0.3MnO3 have a maximum MR% value of 7.3% at room temperature under the applied filed 1 Tesla. La0.7Ba0.3MnO3 thin films were grown preferred orientation on SiO2/Si(100) substrate at 700℃. For the as-deposited film, resistance increases with decreasing temperature, no resistance transition point is seen. The post-anneal at 900℃ for 4 hours, The resistance transition from insulating to metallic occurs at 185K. The lattice constants ( a, c ) decrease after post-annealing. Annealed films show lower electrical resistance than as-deposited ones at the same temperature. The reason is due to oxygen occupancy into the lattice, the oxygen vacancy is decreased, the valence of Mn ion is increased, the diameter of Mn ion is decreased, so the lattice becomes smaller. Because the sputter yield of Ba is different from other species and substrate temperature is high (700℃), the content of Ba is lower than that of the targer and oxygen vacancy appears. Thus MR was not detectable at room temperature. The preferred orientation structure was very important for MR%. For example, at a degree of texture 99.44%, the maximum value of MR% was 30.9%; at a the degree of texture 92.84%, the maximum value of MR% was 16.7% at the same applied field 1.5 Tesla .