【作者】 刘浩；

【导师】 高国营；

【作者基本信息】 华中科技大学 ， 凝聚态物理， 2015， 硕士

【摘要】 半金属铁磁体具有100%的自旋极化率和高的居里温度,是设计自旋电子器件的关键材料。本文采用基于密度泛函理论的第一性原理方法,一方面对二元Heusl er合金DO3-Mn3Ge及其(001)表面的电子结构、磁学性质和表面稳定性进行了研究;另一方面研究了四元霍伊斯勒合金CoR uVSb和CoRuCrSi的结构稳定性、电学、磁学性质以及CoFeMnGe的(001)表面性质。得到以下主要结果:块材DO3-Mn3Ge具有半金属亚铁磁性,其自旋向下方向有一个大约为0.52eV的能隙,总磁矩为1.00Bμ,符合半金属材料的特性。Mn终结的(001)表面由于大的交换劈裂保留了半金属性,而MnGe终结的(001)表面破坏了块状Mn3Ge的半金属性。我们比较了D03-Mn3Ge(001)表面和实验已合成的D02 2-Mn3Ge(001)表面的表面能,发现Mn3Ge的(001)表面除了有DO22相以外还可能有DO3相。DO3-Mn3Ge的表面半金属性和结构稳定性使得它有可能成为潜在的自旋电子材料。四元霍伊斯勒合金CoRuVSb和CoRuCrSi的三种结构中,均在type I结构最稳定,并且都具有半金属性。CoRuVSb的半金属性是非常活跃的,因为当它的平衡晶格常数伸长4.87%或者压缩4.87%时仍然具有半金属性。此外,CoFeMnGe在typ e I结构下的CoFe-(001)和MnGe-(001)表面均失去了块状中的半金属性,但CoFe-te rm(001)表面仍然具有很高的自旋极化率(78%)。更多还原

【Abstract】 Half-metallic ferromagnets, which have 100% spin polarization and high Curie temperatures, are the key to achieve high performance of the spintronic devices. In this thesis, using the first-principles based on the density functional theory, we firstly study the slectronic structure, magnetic property and surface stability of DO3-Mn3Ge and its (001) surface. On the other hand, we study the structural stability, electronic and magnetic properties of the quaternary Heusler alloys CoRuVSb and CoRuCrSi. We also study the surface properties of the CoFeMnGe(001) surface. We obtain the following main results:DO3-Mn3Ge shows half-metallic ferrimagnetism, and there is a band gap about 3.52eV in the spin down direction. The total magnetic moment of DO3-Mn3Ge is 1.00 μB, which is a typical characteristic of half-metallic magnets. The bulk half-metallicity is preserved at the pure Mn-term(001) surface due to the large exchange split, but the MnGe-term (001) surface destroys the bulk half-metallicity. We compare the surface energies of DO3-Mn3Ge (001) surface and experimental D022-Mn3Ge (001) surface, and reveal that the feasibility to grow the Mn3Ge (001) films with DO3 phase other than DO22 one. The surface half-metallicity and stability make DO3-Mn3Ge a promising candidate for spintronic applications.In the three different structures of quaternary Heusler alloys CoRuVSb and CoRuCrSi, both them have the most stable type I structure, and both CoRuVSb and CoRuCrSi with type I structure exhibit excellent half-metallic ferromagnetism. The half-metallicty of CoRuVSb is robust against the lattice compression (up to 4.87%) and expansion (up to 4.87%). In addition, we also find that the half-metallicity of CoFeMnGe with type I structure is lost at its CoFe-and MnGe-terminated (001) surfaces, but the spin polarization is still high at the CoFe-terminated (001) surface (78%).更多还原