Effect on magnetic properties of germanium ...

Effect on magnetic properties of germanium encapsulated C60 fullerene Nibras Mossa Umran and Ranjan Kumar Citation: AIP Conf. Proc. 1512, 264 (2013); doi: 10.1063/1.4791012 View online: http://dx.doi.org/10.1063/1.4791012 View Table of Contents: http://proceedings.aip.org/dbt/dbt.jsp?KEY=APCPCS&Volume=1512&Issue=1 Published by the AIP Publishing LLC.

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Effect on Magnetic Properties of Germanium Encapsulated C60 Fullerene Nibras Mossa Umran, Ranjan Kumar Department of Physics, Panjab University, Chandigarh, India Corresponding author email: [email protected], [email protected] Abstract: Structural and electronic properties of Gen (n=1-4) doped C60 fullerene are investigated with ab initio density functional theory calculations by using an efficient computer code, known as SIESTA. The pseudopotentials are constructed using a Trouiller–Martins scheme, to describe the interaction of valence electrons with the atomic cores. In endohedral doped embedding of more germanium atoms complexes we have seen that complexes are stable and thereafter cage break down. We have also investigated that binding energy, electronic affinity increases and magnetic moment oscillating behavior as the number of semiconductor atoms in C60 fullerene goes on increasing. Keywords: Endohedral doping; magnetic; germanium; Fullerene; C60; Gen@C60. PACS: 61.48.-c, 71.20.Tx, 72.80.Rj, 75.50.Xx.

electron affinity and the magnetic momentum of germanium doped C60 fullerene by optimizing the atomic geometries.

INTRODUCTION Fullerenes are characterized with their capability of forming different types of doping derivatives such as C60, to obtain a conducting molecule from C60, some sort of doping is necessary to provide the charge transfer to move the Fermi level into a band of conducting states. In endohedral doping, atomic orbitals of the dopant interacts with ʌ-orbitals of the shell. It is well known that the icosahedral C60 molecule may have unusual magnetic properties [1]. The magnetic susceptibility of C60 as well as the magnetic field ʌ -electrons ring currents in the carbon spheroid, are also of interest, both Ge and C belong to the same group of elements in the periodic table, but their chemistry is very different and the understanding on interactions between the fullerene and silicon or germanium atoms is of importance to develop new fullerenebased materials, because the doping of Si/Ge atoms to modify the fullerene electronically and geometrically with moderate deformation in bonding [2]. The large empty space in fullerene molecule may be used as storage materials with high capacity and stability. Therefore it becomes pertinent to study the properties of endohedral fullerenes doped with different number of atoms. In the present work we have studied the stability, geometries, binding energies per atom and

COMPUTATIONAL DETAIL We performed ab initio calculations by using an computer code, known as SIESTA [3, 4] which is based on the standard Kohn–Sham selfconsistent density functional theory (DFT). The pseudopotentials are constructed using a Trouiller–Martins scheme [5] to describe the interaction of valence electrons with the atomic cores. The exchange-correlation potential of Perdew–Burkle–Ernzerhof (PBE) for generalized gradient approximation (GGA) corrections are adopted [6]. The atomic orbital set employed throughout was a double-zeta polarization DZP function. For the calculations of cohesive energies, we considered that the ground states of an isolated carbon atom and germanium atom are in the triplet states. Having described the structure of pure C60 we proceed to our calculation on carbon and Ge based system. The binding energy of the endohedral complex is calculated from energy difference between reactants (carbon atom and the relevant number of silicon atoms) and the complex product species. The binding energy is calculated using

SOLID STATE PHYSICS: Proceedings of the 57th DAE Solid State Physics Symposium 2012 AIP Conf. Proc. 1512, 264-265 (2013); doi: 10.1063/1.4791012 © 2013 American Institute of Physics 978-0-7354-1133-3/$30.00

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formula given below.

U Ge= [ EGe n @ C 60 − nE Ge ] n

where as with even number of Ge atoms the magetic moment approchs to zero. The presence of magnetic in Gen@C60 is quite fascinating and a new result indeed. However there have been few reports of magnetic moment in Ge substituted C60 molecule[7]. We conclude that One can accommodate atmost 4 Ge atoms inside C60 without distorting its symmetry and structure. With Ge atoms 1 and 3 we have observed magnetic moment.

(1)

Where UGe is the binding energy per Ge atom encapsulated inside C60. EC60 is the total energy of pure C60 and EGe is the total energy of one Ge atom. EGen@C60 is the total energy of endohedral complex. And EGe is the energy of one isolated Ge atom. The optimized C60 cage structure was used for germanium interaction. We assign initial coordinates to Ge atom and carbon atoms of C60 molecule and allow the system to relax with respect to all degrees of freedom without additional constraints. The structures investigated include Ge atoms varying from 1 to 4. The lowest energy structures of Gen@C60 ( n =1-4) are shown in fig.1.

Gen

Electron Affinity (eV)

     

RESULTS AND DISCUSSION









Number of atoms FIGURE2. Variation of E.A. per atom with n.

In the present work we calculated binding energy per Ge atom, electron affinity and magnetic moment for encapsulation Ge atoms in C60. we put inside fullerene the number of germanium atoms up to n=4, because when n>4 the binding energy became positive. The optimized structures are presented in fig.1. The results are presented in figs 2and 3. We find that when a single Ge atom placed inside C60 the resulting structure is more stable as compared to pure C60.The trend is same with more number of doped Ge atoms. Electron affinity of endohedral complex varies from 2.2 -2.7 eV and is almost same as that of C60.

Gen

Magnetic Moment (μB)

2.0 1.6 1.2 0.8 0.4 0.0 1

2

3

4

Number of atoms

FIGURE 3.Variation of magnetic moment per atom with n.

REFERENCES

Ge1@C60

Ge3@C60

1. H.W. Kroto, J.R. Heath, S.C. O’Brien and R.F. Smalley, Nature 318, 162 (1985). 2. M. Miao Wu, X. Zhou, J. Zhou, Q. Sun, Q. Wang and P. Jena, J. Phys.:Condens. Matter 22, 275303 (2010). 3. P. Ordejón, E. Artacho and J. M. Soler, Phys. Rev. B 53, R10441 (1996). 4. J. M. Soler, E. Artacho, J. D. Gale, A. Garcia, J. Junquera, P. Ordejon, and D. Sanchez-Portal, J. Phys.: Condens. Matter 14, 2745 (2002). 5. N. Troullier and J. L. Martins , Phys. Rev. B.43, 1993 (1991). 6. J.P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996). 7. N. Misra, A. Dwivedi, and A. Pandey, Chin. J. Phys. 50, 64 (2012).

Ge2@C60

Ge4@C60

FIGURE 1. Optimized structure of Gen@C60 (n=1-4)

The clusters having odd number of Ge atoms show a magnetic moment of the order of 2

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