Solid State Communications 151 (2011) 1877–1880 Contents lists available at SciVerse ScienceDirect Solid State Communications journal homepage: www.elsevier.com/locate/ssc Spin transport in bimetallic pentalene complexes Yukihito Matsuura ∗ Department of Chemical Engineering, Nara National College of Technology, 22 Yatacho, Yamato-Koriyama, Nara 639-1080, Japan article info Article history: Received 28 July 2011 Received in revised form 2 October 2011 Accepted 3 October 2011 by G. E. W. Bauer Available online 8 October 2011 Keywords: A. Bimetallic pentalene complex D. Spin transport E. DFT abstract Spin transport in bimetallic pentalene complexes (CpM(pentalene)M ′ Cp; M, M ′ = Fe, Co, Ni) between two gold electrodes was investigated, using a Green’s function formalism under density functional theory. Variation of the metal atom species in the complexes gives a considerable change in their spin properties, with hetero-bimetallic complexes containing an odd number of electrons exhibiting spin filter behaviour. In contrast, alternation in the contact condition, whether Cp-anchoring or adducting by sulphur–gold bonds, had almost no effect on spin filter behaviour, but did lead to variation in electrical conduction. We examined suitable bimetallic pentalene complexes in order to enhance their spin filter efficiency. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Molecular electronics has attracted considerable attention in experimental and theoretical fields [1]. Recent theoretical stud- ies have developed a first-principles Green’s function formalism with density functional theory (DFT), and have focused on the electrical conduction of molecules connected to metal electrodes [2,3]. Molecular spintronic devices, which control the electron cur- rent via the spin-up and spin-down states in organometallic com- pounds, have been studied in both theoretical and experimental fields [4]. In particular, cyclopentadienyl (Cp) ring-transition metal atom multi-decker complexes, such as Cp–Fe, Cp–Ni, and Cp–V multi- decker sandwich complexes, were predicted to exhibit half- metallic properties with spin filter behaviour [5,6]. Organometallic π -complexes, prepared from the pentalene di- anion (Cp ∗ M(pentalene)M ′ Cp ∗ ;M, M ′ = Fe, Co, Ni, Ru; Cp ∗ = pentamethylcyclopentadiene), have been studied extensively be- cause the bridging ligand provides considerable interaction be- tween the two transition metal centres [7]. One of the remarkable properties of these bimetallic pentalene complexes was the charge localization–delocalization transition that was observed us- ing Mössbauer spectroscopy [8]. The hetero-bimetallic pentalene complex (M, M ′ = Fe, Co) had a magnetic moment at room tem- perature with an unpaired electron of the Co atom, while inter- molecular exchange was weak and antiferromagnetically coupled with no cooperative magnetic behaviour [8]. It could be assumed ∗ Tel.: +81 743 55 6158; fax: +81 743 55 6169. E-mail addresses: matsuura@chem.nara-k.ac.jp, parryslane@yahoo.co.jp. that such a bimetallic complex would provide spin filter properties when sandwiched between two metal electrodes. In this study, we investigated the spin transport in bimetallic pentalene complexes between two gold electrodes by using a Green’s function formalism under the DFT. In general, it is well known that a Cp ring energetically prefers to be adsorbed on a Pt(111) surface [9]. Previously, we studied the electronic structure of a Cp–indium multi-decker sandwich complex adsorbed on a Pt or Au surface, and clarified that the complex was energetically stabilized [10]. Therefore, we also designed a Cp-anchoring system for CpM(pentalene) M ′ Cp between the two gold electrodes and examined the spin transport. In contrast, experimentally prepared bimetallic pentalene complexes have a Cp* ring at the end, whose methyl groups may stunt adhesion to the gold surface. As the sulphur atom has a good affinity with the gold surface [11], we also constructed a model of sulphur-substituted bimetallic pentalene complexes (SCpM(pentalene) M ′ CpS) and examined their spin transport properties. 2. Computational method We obtained the relaxed atomic positions of bimetallic pen- talene complexes from the DFT calculation, using the Atomistix Toolkit [12], which is based on the SIESTA code, as the DFT plat- form [13,14]. In the DFT calculation, we employed the local spin density approximation (LSDA) pseudo-potential for exchange cor- relation. A single-ζ plus polarization basis set was adopted for all of the atoms, and the mesh cut-off in the calculation was set at 75 Ry. The geometry optimization was carried out using conjugate gradient relaxation until the forces were smaller than 0.03 eV Å −1 . The scattering region was constructed by the complex (molecular 0038-1098/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2011.10.001