Nearly Perfect Spin Filter, Spin Valve and Negative Differential Resistance Effects in a Fe4-based Single-molecule Junction

Abstract

The spin-polarized transport in a single-molecule magnet Fe 4 sandwiched between two gold electrodes is studied, using nonequilibrium Green's functions in combination with the density-functional theory. We predict that the device possesses spin filter effect (SFE), spin valve effect (SVE), and negative differential resistance (NDR) behavior. Moreover, we also find that the appropriate chemical ligand, coupling the single molecule to leads, is a key factor for manipulating spin-dependent transport. The device containing the methyl ligand behaves as a nearly perfect spin filter with efficiency approaching 100%, and the transport is dominated by transmission through the Fe 4 metal center. However, in the case of phenyl ligand, the spin filter effect seems to be reduced, but the spin valve effect is significantly enhanced with a large magnetoresistance ratio, reaching 1800%. This may be attributed to the blocking effect of the phenyl ligands in mediating transport. Our findings suggest that such a multifunctional molecular device, possessing SVE, NDR and high SFE simultaneously, would be an excellent candidate for spintronics of molecular devices.M olecular spintronics using molecules as spin transport elements has attracted intensive interest due to obtained various functionality, and molecular devices such as spin valve, single-molecule transistors, switch and diode, etc [1][2][3][4][5] . Conventionally, the magnetic molecule junction (MMJ) can be achieved by placing a nonmagnetic molecular bridge between two ferromagnetic electrodes 6,7 . In the rather newer field, MMJ can also be achieved by coupling a magnetic molecule to two nonmagnetic probes [8][9][10] . In this approach, singlemolecule magnets (SMMs) are ideal building blocks to construct MMJ because of their independent magnetically functional units [11][12][13] , where the inner magnetic core in SMMs is surrounded by organic ligands and the interaction between magnetic cores of neighbor molecule is very weak, leading to a large-spin ground state. Unlike above mentioned conventional MMJ depending on reasonable magnetic configuration of two ferromagnetic leads 7,14 , the origin of magnetic behavior in this MMJ consisting of a single-molecule magnet and two nonmagnetic electrodes is the intrinsic spin of the center magnetic molecule, therefore avoiding the great difficulty of the spin injection from ferromagnetic electrodes into a nonmagnetic center in real applications. And so the unique feature of MMJ containing SMM would offer much greater potential for high-density information storage devices 15 .Although there have been some successful efforts to organize SMMs on various substrates, the observation of magnetic hysteresis on individual molecules organized on surfaces 16,17 , that is a necessary step to develop molecular memory arrays, had not been reported for monolayers of SMMs when wired to metallic surfaces until Matteo Mannini and co-workers found that tailor-made tetranuclear Fe 4 complexes retain their magnetic properties at gold surfaces 15 . This...

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