Ag掺杂对La_(0.67)Sr_(0.33)MnO_3磁性和导电性的影响机制研究

Study on conductive and magnetic properties of Ag-doped La_(0.67)Sr_(0.33)MnO_3

稀土掺杂锰氧化物材料La_(0.67)Sr_(0.33)MnO_3(LSMO)的顺磁-铁磁转变温度(Tc)高于室温,在自旋电子学等领域有广泛的应用前景.近年来的研究表明,Ag掺杂能有效改善LSMO的晶粒尺寸和导电性能.本文中采用溶胶-凝胶法制备了La_(0.67)Sr_(0.33)MnO_3:Agx(x=0,0.5%)多晶粉体.采用X线衍射(XRD)、扫描电子显微镜(SEM)、振动样品磁强计(VSM)和X线光电子能谱(XPS)多种技术,测试了Ag掺杂前后LSMO的微观形貌、晶相结构、电阻率、磁滞回线、Ag和Mn元素价态变化.分析表明:一部分Ag以单质形式存在于LSMO晶粒边界,增强了导电性;另一部分Ag进入晶格,替代了钙钛矿结构ABO3的A位La离子,使LSMO中出现少量La2O3杂相,并使Mn3+/Mn4+比例降低,削弱了双交换作用,因此LSMO的磁性减弱.Ag替代La还使LSMO的少数自旋子带带隙略减小,对提高导电性有次要的负作用.

Rare-earth doped manganese oxide La0.67Sr0.33MnO3（LSMO） has broad application prospects in the field of spin electronics,which has the paramagnetic-ferromagnetic transition temperature（ Tc） above room temperature. Recent research shows that Ag-doping has effective improvements of grain size and conductivity of LSMO for improving the colossal magnetoresistance effect（ CMR）. In this paper,sol-gel method was used to prepare La0.67Sr0.33MnO3：Agx（x = 0,0. 5%） polycrystalline powder. By X-ray diffraction（ XRD）,scanning electron microscopy（ SEM）,vibrating sample magnetometer（ VSM） and X-ray photoelectron spectroscopy（XPS） technologies,the microstructure,crystalline phase structure,resistivity,magnetic properties,Ag and Mn valence states of LSMO were tested before and after Ag doping,respectively. The analysis shows that some Ag atoms exist at the grain boundary of LSMO in the form of element to enhance the conductivity,and other Ag atoms go into the crystal lattice replacing A site La^3＋ in the perovskite structure ABO3,which obtains a small amount of La2O3 hybrid phase in LSMO and decreases the ratio of Mn^3＋/Mn^4＋. Ag doping weakens the double exchange effect and the magnetic property of LSMO. The substitution of La with Ag also makes minority spinon band of LSMO slightly reduced,which can weakly decrease the conductivity of LSMO.