Computational Modeling of Spin Couplings in Self-Assembled Fe-PTCDA Molecular Nanowires
Date Issued
2014
Date
2014
Author(s)
Hsu, Shih-Hao
Abstract
Self-assembled Fe-PTCDA complexes on Au(111) surface can form very long nanowires which have promising properties for molecular spintronics. In this work, we explore the geometries, electronic structures and magnetic properties of Fe-PTCDA nanowires, with and without the Au substrate, using density functional theory calculations. Based on the geometries of Fe-PTCDA nanowires, there are 4 types of spin configurations, and the electronic structures are strongly dependent on the spin configurations, i.e. the magnetism. On the geometry, the free-standing Fe-PTCDA nanowires are planar and the Fe-PTCDA nanowires on Au(111) become bent after adsorption. Moreover, because the Fe orbitals involved in the hybridization in the bent nanowires are different from the ones in the planar free-standing nanowires, the ground state spin configuration is changed after adsorption. As a conclusion, the geometry is critical for the magnetism of the Fe-PTCDA nanowires. In addition, the strength of spin couplings between Fe atoms, through delocalized molecular orbitals or substrate RKKY coupling, is estimated by using the Heisenberg model. In the planar free-standing nanowires, the couplings through the molecular orbitals align the spins parallel, while in the bent nanowires, the spins are aligned antiparallel. The changes of the spin couplings can be attributed to the change of hybridizations. Finally, by estimating the RKKY interaction on Au(111) surface, the couplings through the molecular orbitals are found to be dominant in the adsorbed Fe-PTCDA nanowires.
Subjects
密度泛函理論
分子自旋電子學
金屬－有機介面
奈米線
苝四甲酸二酐
自旋耦合
海森堡模型
RKKY效應
Type
thesis
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