Theory Study On Structure And Magnetic Properties Of CoSn And CoAl Alloy Clusters

The bimetallic transition metal(TM)clusters by applying a controlled chemical composition and size,which can become heterogeneous nanomaterials with potentially special function.Therefore,the study of the electronic structure and magnetic properties of bimetallic TM clusters have become a hot research topic in the field of cluster physics.However,how to choose the type of doping elements,composition,arrangement of atoms and the size to further obtain the new electromagnetic properties of bimetallic TM clusters have become a key issue of its application research.In addition,bimetallic TM clusters are suitable for candidates for potential application in chemical catalysis,optic,solid state and magnetic non-material by enriching its physical and chemical properties.Co based transition metal clusters have attracted more attention from researchers due to their unique magnetic properties.In theory,the equilibrium geometries,relative stabilities,electronic stabilities,and magnetic properties of MSn12(M=Ti?V?Cr?Mn?Fe?Co?Ni)clusters have been systematically investigated.Results show that the magnetic moments of MSn12 vary from 2?B to 5?B.It is indicated that the MSn12 cluster is a new kind of potential nano magnetic materials.In addition,Deshpande studies on the doping of ferromagnetic Ni clusters by the non-magnetic Sn atoms will lead to the increase of the binding energy and the decrease of the magnetic properties.There is little relevant research about Co-Sn alloy clusters.Therefore,based on the first principles density functional theory,we selected the tin atom as an impurity atom to study the most stable structures,electronic properties as well as the magnetic moments of ConSn(n=1-12)clusters.We attempt to study how the doped Sn atom impacts upon the magnetic behavior of Con clusters.The Stern-Gerlach magnetic deflection molecular beam experiment of CoAl alloy clusters shown that each one of the Al atoms doped for CoNAlM(N?60,M?N/3)clusters,the magnetic moment decreased 3.9?B.Results shown that the magnetic reduction does not depend on the composition and size of CoNAlM clusters.However,the Stern-Gerlach magnetic deflection experiment provides weak information on the other properties of the clusters,such as geometry and electronic structure.In our knowledge system,the theoretical study on the magnetic properties of CoAl alloy clusters with larger proportions has not been reported.In order to gain a comprehensive understanding of the structure and magnetic properties of CoAl clusters,we study the structural evolution and magnetic properties of Co13-nAln(n=0-13)transition metal clusters with large size and proportion.The structure and magnetic properties of Co13-nAln alloy clusters were obtained to explain the experimental phenomena and to understand the physical mechanism of the magnetic changes.The main contents and results are as follows:(1)Equilibrium geometries,relative stabilities,electronic stabilities,and magnetic properties of Con Sn(n=1-12)clusters have been systematically investigated by using relativistic all-electron density functional theory with generalized gradient approximation.The results indicated that the lowest-energy structures of ConSn(n=1–5,7,9,10)clusters are similar to those of corresponding Con+1 clusters.As for Co6 Sn,Co8Sn,Co11 Sn and Co12 Sn clusters,the most stable structures give rise to a geometry reconstruction.In the low-lying structures of ConSn(n=1–12)clusters,tin impurity prefers to occupy the external position.The second-order difference energy ofthe ground-state ConSn(n=1–12)clusters show a pronounced odd-even oscillation with the number of Co atoms,and the clusters exhibit higher stability at n=5.Compared with corresponding pure Con+1 clusters,the total magnetic moment of the ConSn clusters reduce with 1?B,3?B and 5?B,respectively.For ConSn(n=1-3,5-7)clusters,the total magnetic moment decrease 3?B,while for Co4 Sn reduces 5?B.The magnetic moment of Con Sn(n=8-12)clusters only change 1?B.The average bond length and average coordination number of Con Sn and Con+1(n=1-12)clusters present a similar trend with the variation of size,which is owing to their similar structures.Results show that the average bong length dominates the change of magnetic moment of Con Sn clusters.In addition,the density of States and Muliken analysis results show that the orbital hybridization as well as the charge transfer may be another major reason for the changes of magnetic moment of Con Sn clusters.(2)Based on the first principle,we use the Vienna Abinitio Simulation Package(VASP)software and combine with the generalized gradient approximation(GGA)and pseudopotential plane wave basis set to study the structures,electronic and magnetic properties of Co13-nAln(n=0-13)clusters.All the most stable structures of Co13-nAln(n=0-13)clusters are performed through the CALYPSO package.Results show that the most stable structure for Co13 cluster is a hexagonal close packed(hcp)structure,in good agreement with the recent theoretical calculations.The Co12 Al cluster is an hcp structure with Al occupied the vertex position.The icosahedra structure is more stable for Co13-nAln(n=2-6)clusters.When n=7-10,the system still tends to the growth pattern of the icosahedra structure,however,the most stable structure of Co2Al11 and CoAl12 clusters give rise to a geometry reconstruction.It is more inclined to form an hcp structure.In our work,the Al13 cluster is a classical icosahedron configuration agreement with previous theoretical calculations.Results show that the Al atoms trend to be in the surface of alloys while the Co atoms trend to be in the center.And the stability of Co13-nAln clusters decreases with increasing aluminum atoms.The magnetic moment of Co13-nAln clusters are reduced,and the magnitude of the magnetic reduction is consistent with the experimental results of CoNAlM(N<60,M<N/3).It is found that the magnetic order of Co13-n Aln clusters are anti-ferromagnetic coupling(expect Co11Al2).The decrease of the spin density of cobalt atoms is the main reason for the decrease of the magnetic properties for Co13-n Aln clusters.