Reshi Hilal Ahmad, Pillai Shreeja, Bhuwal Deepika, Shelke Vilas
Novel Materials Research Laboratory, Department of Physics, Barkatullah University, Bhopal 462026, Madhya Pradesh, India.
J Nanosci Nanotechnol. 2013 Jul;13(7):4608-15. doi: 10.1166/jnn.2013.7136.
We investigated implications of nanostructure formation on structural and magnetotransport properties of La0.7Sr0.3MnO3 compound. The polycrystalline nanomaterials of variable grain sizes were synthesized by using sol-gel method. The structural parameters obtained by Rietveld refinement of the X-ray diffraction data indicated that the samples possess perovskite structure with orthorhombic Pnma symmetry. The X-ray Photoemission Spectra showed chemical shift in the lowest particle size sample due to oxygen deficiency. The average particle size observed through transmission electron microscopy varied from 22 nm to 34 nm. The particle size induced metal-insulator transition and substantial increase in electrical resistivity observed in these nanomaterials are in contrast with the bulk material phase diagram. We also observed temperature and magnetic field dependent colossal magnetoresistance. The low-field magnetoresistance is substantially enhanced in nanomaterials samples, making it more promising for device applications. A divergence in field cooled and zero field cooled magnetization indicated possibility of magnetic spin-glass behavior.
我们研究了纳米结构形成对La0.7Sr0.3MnO3化合物的结构和磁输运性质的影响。采用溶胶-凝胶法合成了具有可变晶粒尺寸的多晶纳米材料。通过对X射线衍射数据进行Rietveld精修得到的结构参数表明，样品具有正交Pnma对称性的钙钛矿结构。X射线光电子能谱显示，由于氧缺陷，在最小粒径样品中出现了化学位移。通过透射电子显微镜观察到的平均粒径在22纳米至34纳米之间变化。这些纳米材料中观察到的粒径诱导金属-绝缘体转变以及电阻率的大幅增加与块状材料相图形成对比。我们还观察到了温度和磁场依赖的巨磁电阻。纳米材料样品中的低场磁电阻显著增强，使其在器件应用方面更具前景。场冷和零场冷磁化强度的差异表明存在磁自旋玻璃行为的可能性。
