La1-xCaxMnO3的电子结构与磁有序研究

Electronic Structure and Magnetic Order of Perovskite Material La_(1-x)Ca_xMnO_3

采用DV-Xa分子轨道法计算了不同掺杂浓度的立方结构钙钛矿La_(1-x)Ca_xMnO_3体系的电子结构,分析了体系磁电特性随钙浓度变化的特征.结果表明:自旋相关的锰3d—氧2p轨道杂化出现在整个体系中.未掺杂体系具有金属型导电性,费米能级处多数自旋子带的态密度高于少数子带.随着掺杂浓度的提高,体系发生金属-半金属相变.与此同时,锰离子磁矩单调降低,与3d带自旋交换劈裂的变化规律一致.掺杂的钙提高了锰3d和氧2p电子波函数的交迭,加强了Mn-O-Mn超交换作用,使CaMnO3呈现G型反铁磁态.LaMnO_3中锰3d和氧2p波函数的交迭最弱,呈铁磁有序.

DV-Xa molecular orbital method was employed to study the electronic structure of perovskite La1-x CaxMnO3 cubic system where the dopant concentrations are different. The dependence of magnetic and electrical properties on the dopant calcium concentration have been investigated. It was found that the spin-dependent Mn3d--O2p hybridization occurs in the whole perovskite La1-xCaxMnO3 system. The conductivity of the undoped system is metallic and the DOS （density of state） at Fermi level in major bands is higher than that in minor bands. With the increase in dopant concentration x, the conductivity of the manganite changes from metallic to half-metallic and the magnetic moment of Mn decreases monotonously in conformity with the changing regularity of the exchange splitting of Mn3d bands. The doped Ca increases the overlap of Mn3d and O2p orbits to intensify the Mn--O--Mn superexchange and cause the magnetic ordering of CaMnO3 to present G-type antiferromagnetism. Meanwhile, LaMnO3 presents orderly ferromagnetism due to the weak overlap of Mn3d and O2p.