La_(0.67)Sr_(0.33-x)Ag_(x-y□y)MnO_3/Ag_y多晶材料的磁电阻

Magnetoresistance of La_(0.67)Sr_(0.33-x-y)Ag_(x-y□y)MnO_3/Agy polycrystalline

采用溶胶-凝胶(sol-gel)法制备La0.67Sr0.33-xAgx-y□yMnO3/Agy(x=0.20,0.30)多晶粉末,经压制与1 400℃/12h烧结获得相应的块体材料,借助X射线衍射仪(XRD)、扫描电镜(SEM)、透射电镜(TEM)和多功能物性测量系统(PPMS,附件VSM),对材料的相结构、微观结构和磁性能进行研究。结果表明:La0.67Sr0.33-xAgx-y□yMnO3/Agy粉末形貌为接近球形的凸多面体,平均粒度在150 nm左右,块体材料结构致密但粒度变大。另外,粉末与块体材料中都有金属Ag相和Sr空位存在。在室温下块体材料的磁电阻较小,而且为负值。在低温区,外加磁场越高,则磁电阻越大,在外加磁场为3T、温度为174和20 K条件下,La0.67Sr0.13Ag0.20-y□yMnO3/Agy的磁电阻分别为-37.5%和-43.3%,在141和20 K温度下La0.67Sr0.03Ag0.30-y□yMnO3/Agy的磁电阻分别为-45.1%和-53.9%。

Polycrystalline powders of La0.67Sr0.33-xAgx-y□yMnO3/Agy（x=0.20,0.30） were prepared by sol-gel method, then the powders were pressed and sintered at 1 400 ℃ for 12h to obtain the corresponding bulk samples. The phase composition, microstructure and magnetic properties of samples were investigated by X ray diffraction （XRD）, scanning electron microscope （SEM）, transmission electron microscope （TEM） and physical property measurement system（PPMS, Accessory VSM） techniques. The results demonstrate that morphology of La0.67Sr0.33-xAgx-y□yMnO3/Agy powders shows a convex polyhedron sphericity and the average particle size is about 150nm. The bulk samples have compact structure and their grain size become larger. In addition, the phase of Ag and Sr vacancies exist in both powder and bulk samples. At room temperature, magnetoresistance of bulk samples is small and negative. At low temperature, magnetoresistance increases with increasing the magnetic field, under 3 T magnetic field, the magnetoresistances of La0.67Sr0.13 Ag0.20-y□yMnO3/Agy are -37.5% and -43.3% at 174 K and 20 K, respectively. The magnetoresistances of La0.67Sr0.03Ag0.30-y□yMnO3/Agy are-45.1%and-53.9%at 141 K and 20 K respectively.