1、2023年11月Nov.2023文章编号：10 0 1-42 17(2 0 2 3)0 6-0 0 6 4-0 7汕头大学学报（自然科学版）Journal of Shantou University(Natural Science)第38 卷第4期Vol.38 No.4第一性原理研究Sr(Fei-xPtx)2AS2中的反铁磁抑制与共存李力，王红丽，王伟芳，樊丽丽，王金环，陈立宇，郝璞玉，贾东芳（唐山师范学院数学与计算科学学院，河北唐山0 6 30 0 0）摘要为了研究Sr(FeixPt)2As2（x=0,0.12 5)的电子结构和磁学性质，借助第一性原理研究了0 K时不同磁序中的体系能量和海森
2、堡模型，计算表明共线反铁磁序是母体化合物的基态.对Fe磁矩和耦合常数的变化分析表明，Pt掺杂可以抑制SrFe2As2中反铁磁序.Pt掺杂使布里渊区中心处(x=0)的空穴费米面嵌套演变成为电子费米面（x=0.125)的拓扑结构.态密度分析表明，Fe3d电子的巡游性增强.在x=0.125的超导化合物中，耦合常数分析表明共线反铁磁序仍然存在。关键词第一性原理；铁基超导体；反铁磁序；海森堡模型中图分类号0 46 9文献标识码A1 引 言继铜酸盐之后，铁基超导体的发现掀起了超导研究的新高潮.在F掺杂LaOFeAs中观察到超导现象，超导体的转变温度（T.)约为2 6 K.随后DOFeAs(D=Ce，Sm，
3、Nd，G d等)的报告显示T。超过45 K2，其中SmOixF,JFeAs的T。达到5 5 K3.随后，12 2 家族 4-6 的EFe2As2(E=Ba，Ca，Sr)迅速进人研究人员的视野，更容易制备出高质量的晶体样品l；其中，SrFe2xM,As2(M=Ru，Co，Ni，Rh，Pt 等)的掺杂也先后得到了研究 8-9 .在一些基本性质方面，实验报道单晶和多晶样本的研究得出了不同的结论 9-10，因此借助理论计算得出的结论具有特殊的意义.在铁基超导体的研究中，逐渐形成了相对统一的认识：反铁磁（AFM)序与超导态之间存在竞争关系 叫.为了抑制AFM诱导超导，通常采用碱金属或过渡金属掺杂 12
4、和施加外压113.虽然超导态与AFM之间的竞争已被广泛认识，但高温超导的机理仍在探索中.在对12 2 家族的研究中，有的掺杂实验发现了超导态和AFM序在微观水平 4的共存，收稿日期：2 0 2 3-0 1-13作者简介：李力（19 7 9），男（汉族），河北唐山人，工学博士.研究方向：功能材料.E-mail：L i L i 2 0 6 4 16 3.c o m基金项目：河北省高等学校科学技术研究项目（ZC2023016）；唐山师范学院博士基金项目（2 0 2 3B22）第4期也有发现了相分离的情形5 .从理论上讲，AFM序在超导掺杂范围内是否仍然存在已成为我们感兴趣的问题之一。在电子结构和磁机
5、理的研究中，一种观点认为电子费米面(FS)和空穴费米面的嵌套决定了低温下反铁磁条纹的排列顺序 16-17，另一种观点认为自旋构型的形成是由于原子18 的超交换相互作用.对电子结构的分析同样应用于对铁基超导塌缩相和非塌缩相的研究中 19 .本文主要研究了在0 K下，Pt掺杂SrFe2As2布里渊区中心T和Z点附近费米面嵌套的变化，这种变化反映了AFM和超导竞争在铁基超导体中的作用.同时，为了说明Pt掺杂对超交换的影响，利用了Heisenberg模型计算交换耦合常数.2模型与计算方法采用基于密度泛函理论的CASTEP程序包进行计算.SrFe2As2的低温结构为Fmmm20,SrFe2As的晶格常数
6、（A)为a=5.5783(0)，b=5.5 17 5(0)和c=12.296(5).这里使用含有20个原子的111超胞来进行计算.李力等：第一性原理研究Sr(FeixPt)2As2中的反铁磁抑制与共存65SrAsFePt6图1Pt掺杂SrFe2Asz时2 0 个原子超胞模型与Fe平面上最近邻和次最近邻交换耦合常数Ji，J基于密度泛函理论，采用平面波法进行计算.布里渊区采样由12 12 6Monkhorst-Packk点网格给出.利用广义梯度近似(GGA-WC)中Wu和Cohen提出的交换相关函数 2 ，计算出了不同磁序的体系能量.在计算中，截断能设置为45 0 eV，自洽收敛精度采用2 10-
7、5 eV/atom，对原子最大受力的收敛准则为0.0 5 eV/A.最大位移和最大应力分别为2 10 nm和0.1GPa.初步结果表明，在较高的收敛准则下，上述参数保持不变.66汕头大学学报（自然科学版）第38 卷3结果与讨论我们对SrFe2As2和Sr(Fei-xPtx)As2的结构进行了优化，优化后的晶格参数和磁矩随共线AFM的变化如表1所示.结果表明，Pt的掺杂使Fe的磁矩由1.9 2 B/Fe降低到1.82857(1）B/Fe.在优化结构后，我们计算了四种不同磁序的体系能量：棋盘反铁磁序（A F,），共线反铁磁序（AF2），铁磁序（FM)和无磁态（NM).我们发现共线AFM序的体系能量
8、最低（见表2).这意味着共线反铁磁序在低温下为基态，这与文献 2 2 相同.表1共线反铁磁序下，优化了Sr(Fer-Pt)2As,在x=0和x=0.125的晶格参数和Fe磁矩M.Expt.a(A)5.578 3(3)ab(A)5.517 5(3)ac(A)12.296 5(6)a&9090a901V(A)378.46(1)aM(up/Fe)1.69b,2.1Referencel2,bReference124,Referencel25表2 Sr(Fei-,Pt,)2As,在x=0和x=0.125时的JiJ,以及Sr(Fei-,Pt,)2As2(x=0和x=0.125)在四种不同磁序下的总能量：棋
9、盘AFM序（AF）、共线反铁磁序（AF,）、铁磁序（FM)和非磁性态（NM)。Energy(meV)AFAF2FMNMJJ2J./2J2在基态下，计算了Sr(FeixPt)2As2(x=0,0.125)的DOS和PDOS，结果如图2 所示.从图中可以看出，DOS主要来自于Fe3d和As4p轨道的贡献，而在费米能级(Er)附近，DOS主要来自于Fe3d轨道的贡献.当掺杂Pt达到x=0.125时，费米能级向导带方向移动，N(Er)由12.336 1(7)states/eV增加到12.8 0 40(8）states/eV.计算表明，Fe3d与As 4p杂化带宽度由9.318 0（8）eV（Sr Fe
10、 2 A s 2）增加到10.312 0（4）eV(Sr(Feo.875Pto.125)2As2）.同时，掺杂后各Fe的磁矩由1.9 2 B/Fe降低到1.8 2 8 5 7（1）B/Fe，这意味着Fe3d的电子局域化特性变弱，而流动性增强.X=05.556 78(7)5.475 47(3)12.154 48(4)90.000 00(0)90.000 00(0)90.000 00(0)369.812.74(7)1.920 00(0)Different concentrationsSrFe,As2-11635 589.012 6(2)-11 636 179.367 3(5)-11 635 497
11、.298 2(0)-11 635 218.887 3(7)22.928 60(5)159.052.98(5)0.072 078 51(2)X=0.1255.620 91(1)5.541 37(4)12.179 93(7)89.99957(9)90.000 37(2)90.002.76(2)379.375.44(6)1.828 57(1)Sr(Feo.87sPto.125)2As2-11490.652.810 85-11 490 892.741 02-11490 590.34263-11 490 494.241 6315.617 05(5)67.791 0(7)0.115 185 193(3)第
12、4期李力等：第一性原理研究Sr(Fei-xPt)2As2中的反铁磁抑制与共存6730(a)2010030(b)20100-7图2 共线反铁磁序下，Sr(Fei-xPt)2As2在x=0(a)和0.12 5(b)的DOS和PDOS图能带图见图3.未掺杂时，SrFe2As2自旋向上和自旋向下的能带是重合的，在T和Z点，分别有一条价带向上通过费米能级.随着Pt的掺杂，费米能级向上移动，这与分析前面的DOS图时得到的结论同样.费米能级的上移使得部分原本在T和Z点穿过费米能级的能带，此时完全位于费米能级之下，而部分导带向下弯曲并折叠通过费米能级.Pt掺杂使价带在M和A点附近向上越过了费米能级.2.5(a
13、)2.01.51.00.50.0-0.5-1.0-1.5-2.0-2.5MF图3共线反铁磁序下的能带图。（a)SrFe2Asz的能带结构.（b）Sr(Fe i-,Pt）2 A s,在x=0.125时的能带结构在图4中绘制了SrFe2As2在0 K时的费米面.SrFe2As2的费米面在T与Z点形成了嵌套关系.随着Pt的掺杂，原来与Z处的空穴型费米面消失了，并演化为电子型费米面.空穴型费米面的嵌套只形成于M点和A点附近.为了反映掺杂对超交换的影响，本文利用Ma等 2 6 提出的Heisenberg模型计算了交换耦合常数，如表2 所示.结果表明，掺杂后J和J2的交换耦合常数降低，磁矩和交换耦合常数的
14、降低表明反铁磁序被抑制.计算表明，Sr(Fei-xPt)2As2(x=0,0.125)的J/2J21,说明它们均为共线反铁磁序.同时，有研究工作 2 7 已经表明，当x=0.125时Sr(Fei-xPt.)2As2Sum.-Fe-3d.As-4p-SumFe-3dAs-4d-Pt-3d-6-5XMZQAZRAM-4W1I-3Energy/ev(b)2.52.01.51.00.50.0-0.5-1.0-1.5-2.0-2.5MF-2-10XM12QA3ZRAM68处于超导状态，此时我们的计算结果可为超导态与共线反铁磁共存提供支持.Q(a)E汕头大学学报（自然科学版）(b)M第38 卷RFX(a)
15、布里渊区4结论借助CASTEP，我们研究了SrFe2As2在OK下的电子结构和磁学性质.DOS分析表明，Pt掺杂削弱了Fe3d轨道电子的局域性，增强了电子巡游性.随着Pt的掺杂，布里渊区中心I和乙点附近的空穴费米面嵌套转变为电子费米面的拓扑结构.利用海森堡模型研究了Pt掺杂对超交换的影响，超交换耦合常数J和J2随Fe磁矩的减小而减小.掺杂Pt有助于抑制SrFe2As2中的AFM.对于SrFe2AS2，计算表明J/2J1，这表明，无论从四种不同磁序下的体系能量比较，还是从Heisenberg模型来看，共线反铁磁序均为基态.同时计算表明，在超导浓度（x=0.125)时J/2J1，这意味着共线反铁磁
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31、DRYE T,et al.Superconductivity and magnetism in platinum-substituted SrFe2As2 single crystalsJJ.Physical Review B,2010,82:144518.(下转第8 0 页）李力等：第一性原理研究Sr(Fei-xPt)2As2中的反铁磁抑制与共存6980Deformation Characteristics and Chronology ofZhengguo Ductile Shear Zone in Guangdong ProvinceXU Guanjun,YANG Weibin,HE B
32、in,LONG Gui,CHENG Liangkai(Guangdong Geological Survey Institute,Guangzhou 510080,Guangdong,China)Abstract The ductile shear zone is widely exposed in the transitional area between the Yangtze Block andthe Cathaysia Block of the South China plate.The Mesozoic tectonic movement and magmatic activity
33、of theductile shear zone were deeply influenced by the subduction of the adjacent oceanic plate since theJurassic,which is of great significance for understanding the characteristics and processes of the deep crustof the large intra-continent deformation zone under the background of plate activity.B
34、ased on thesystematic investigation of in-situ macroscopic and indoor microscopic characteristics,a prominent ductileshear zone has for the first time been determined in Zengcheng area,Guangdong Province.Moreover,the40Ar/Ar chronology data of single mica grains in the shear zone are used to constrai
35、n the deformation age ofthe zone.In this paper,the geometrical and kinematic characteristics of the shear zone show that the ductileshear zone that has the character of both thrust and sinistral strike-slip.The 40Ar/39Ar dating on single micagrains and plateau ages obtained are(160.80 0.65)Ma and(16
36、0.17 0.65)Ma,respectively,from theZhengguo ductile shear zone.It is inferred that the Zhenggou ductile shear zone was probably formed in theearly Late Jurassic.Combined with the regional geological data and the zircon U-Pb age(161.9 2.6)Ma inthis study,the formation features of granites on the weste
37、rn side of Zhengguo ductile shear zone mayindicate a strong collision between the Pacific plate and the Cathaysia Block in the early periods of LateJurassic,characterized by the horizontal contraction and oblique convergence,Thus,this study providesnew data for further understanding the Yanshan move
38、ment in South China.Keywords Zhengguo ductile shear zone;deformation characteristics;0Ar-39Ar geochronology(上接第6 9 页）Study of Antiferromagnetic Suppression andCoexistence in Sr(Fei-Pt,)2As2 by First PrincipleLI Li,WANG Hongli,WANG Weifang,FAN Lili,WANG Jinhuan,(School of Mathematics and Computationa
39、l Sciences,Tangshan Normal University,Tangshan 063000,Hebei,China)Abstract The electronic structure and magnetic properties of Sr(Fei.Pt,)As(x=0,0.125)arestudied by the first principle.At O K,the energy of different magnetic orders and Heisenberg modelcalculations show that the collinear antiferroma
40、gnetic order is the ground state of the parentcompound.The analysis of the change of the magnetic moment of Fe and the coupling constants showsthat Pt doping can suppress the AFM order in SrFe2As2.Pt doping makes the nesting of hole Fermisurface in the center of Brillouin zone(x=O)become the topolog
41、ical structure of electronic Fermisurface(x=0.125).The analysis of the density of states shows that the itinerancy of Fe 3d electrons isenhanced.In the superconducting compound of x=0.125,the analysis of the coupling constantsshows that the collinear antiferromagnetic order still exists.Key words first principle calculations;iron-based superconductor;antiferromagnetic superexchange汕头大学学报（自然科学版）CHEN Liyu,HAO Puyu,JIA Dongfang第38 卷
