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1、Rare Metal Materials and Engineering Volume 41, Issue 8, August 2012 Online English edition of the Chinese language journal Cite this article as: Rare Metal Materials and Engineering, 2012, 41(8): 1341-1345. Received date: August 09, 2011 Foundation item: the National Natural Science Foundation of C
2、hina (50588201, 50872116); the National High-Tech Research Program of China (2007AA03Z203); the PCSIRT of the Ministry of Education of China (IRT0751); the Innovation Fund for Ph. D. Students of Southwest Jiaotong University (2009); Fundamental Re- search Funds for the Central Universities (SWJTU09B
3、R154, SWJTU09ZT24); the SRFDP (200806130023, 200806130034); and the Australian Research Council (DP0559872, DP0881739) Corresponding author: Pan Min, Candidate for Ph. D., Superconductivity R Zhao Yong, Professor, Tel: 0086-28-87600786, E-mail: Copyright 2012, Northwest Institute for Nonferrous Met
4、al Research. Published by Elsevier BV. All rights reserved. ARTICLEFirst-principles Study of Lattice, Magnetism and Elec- tronic Structure for Fe-Based Superconductors: LaOFeAs, AFeFirst-principles Study of Lattice, Magnetism and Elec- tronic Structure for Fe-Based Superconductors: LaOFeAs, AFe2 2As
5、As2 2 (A=Sr, Ca), MFeAs (M=Li, Na) and FeSe (A=Sr, Ca), MFeAs (M=Li, Na) and FeSe Pan Min1, Feng Yong2, Cheng Cuihua3, Zhao Yong1,3 1 Key Laboratory of Advanced Technology of Materials (Ministry of Education), Southwest Jiaotong University, Chengdu 610031, China; 2 Northwest Institute for Nonferrous
6、 Metal Research, Xian 710016, China; 3 University of New South Wales, Sydney 2052, Australia Abstract: Using density functional theory (DFT) within the scheme of the linearized augmented plane wave and the improved local orbital (APW+lo), we investigated the newly discovered FeAs layered compounds L
7、aOFeAs, SrFe2As2, CaFe2As2, LiFeAs, NaFeAs and FeSe. We report the crystal structures, magnetism, and electronic properties of these Fe-based materials. The results reveal a close correlation of the superconductivity of these FeAs superconductors with the lattice geometry formation and magnetism of
8、their parent compounds. The maximal critical temperatures Tc could simultaneously increase with the decrease of distortion of the FeAs4 tetrahedrons and the increase of interlayer distance L between two FeAs layers. We have further found that the magnetism is mainly attributed to Fe moment, and As 4
9、p and Fe 3d hybrid states affect the physical natures, which are the common feature in these Fe-pnictide superconductors. Key words: Fe-based superconductor; structure; electronic property; magnetism Since Hosonos group started searching for superconduc- tivity in quaternary rare-earth transition me
10、tal oxypnictides a few years ago, the superconductivity has been found in ROTPn, where R= La, T= Ni, and Fe, Pn= P and As. After the report of transition temperatures (Tc) up to 26 K in F-substituted LaOFeAs (called an “1111” type)1, the Tc was quickly elevated up to 5556 K in other doped GdOFeAs sa
11、mples2. Most remarkably, the superconductiv- ity was found to be in the vicinity of a spin-density wave (SDW)3. Afterwards, superconductors based on the parent AFe2As2 system (abbreviated as “122”, A=Ca, Sr, Ba) with Tc up to 38 K were synthesized4, and LiFeAs5 with the PbFCl structure type and cont
12、aining anit-PbO-type FeAs layers were found as a superconductor below 18 K which was defined as a “111” system. Recently, superconductivity has also been discovered with Tc as 8 K in FeSe6, which has a tetragonal Pb-O type structure (space group P4/nmm) at room temperature and planar FeSe alike slab
13、s, which can be defined as a “011” system. The common feature in these Fe-pnictide superconductors is the presence of FeAs plane or Fe(Te/Se). Basically, Fe atoms are from a regular square lattice just like CuO2 plane in cuprates7. However, the dis- tinct As ions are not located between two Fe ions
14、but rather above or below the center of Fe-square. This arrangement of As ions brings notable consequences in the electronic and magnetic properties of these systems. The Fe-Fe dis- tance is not large, allowing direct interaction of Fe atoms that plays an important role in the electronic structure f
15、or- mation near the Fermi level. The Fe-As-Fe angles for the FeAs4 tetrahedrons are also the significant factors which influence the spin and charge interactions between Fe atoms, most likely leading to a change in their Tc8. In addition, Pan Min et al. / Rare Metal Materials and Engineering, 2012,
16、41(8): 1341-1345 researchers have proposed an empirical correlation between maximal Tc and spacing between neighbouring FeAs-FeAs layers 9, and the maximal critical tempera- tures Tc simultaneously increase with the increasing of FeAs-FeAs interlayer distances, L. In this work, we focus on the structural, electronic and magnetism properties of LaOFeAs, AFe2As2 (A=Sr, Ca), MFeAs (M=Li, Na) and Fe
