Electron transport through Ni/1,4-benzenedithiol/Ni single-molecule junctions under magnetic field

Abstract

We have studied electron transport through Ni/1,4-benzenedithiol (BDT)/Ni single molecule junctions at cryogenic temperatures under magnetic field up to 250 mT. Instead of examining magnetoresistance (MR) of individual junctions, we measured the conductance of many junctions under a constant magnetic field and investigated how a single-molecule peak in a conductance histogram shifts with the field strength. We found that the single-molecule resistance at 77 K, deduced from the conductance peak position, shows a hysteresis against the field strength and takes a maximum around 50 mT when the magnetic field increases from 0 T to 150 mT. The observed resistance change yields a MR of $ð80À90Þ% for Ni/BDT/Ni single molecule junctions. This MR is higher than experimental MR reported for non-conjugating molecules but consistent with high theoretical MR predicted for p-conjugated molecules such as BDT. We have also investigated the nonlinearity of the current-voltage (IÀV) characteristics of Ni/BDT/Ni junctions under 0 T and 150 mT and found that the nonlinearity changes its sign from negative at 0 T to positive at 150 mT. This result suggests that the junction transmission spectrum at 0 T should have a low-lying peak within 60:1 eV from the Fermi level, but the peak moves out of the bias window when the magnetic field increases to 150 mT. The observed field-induced change in the IÀV nonlinearity is qualitatively consistent with theoretical IÀV curves of Ni/BDT/Ni calculated for magnetized and non-magnetized Ni electrodes. V

Giant amplification of tunnel magnetoresistance in a molecular junction: Molecular spin-valve transistor

“…6 In a pioneering attempt, researchers have recently fabricated a Ni/1,4-benzenedithiol/Ni spin-valve junction using the break junction technique. 7,8 They reported a very high magnetoresistance as predicted from theory. [11][12][13] Until now, only two-terminal, molecular spin-valve (MSV) junctions have received major attention.…”

“…With the strong demand for downsizing the TMR device and the tremendous progress in nanotechnology in recent years, it has now been possible to demonstrate the TMR effect in a single molecular junction. [5][6][7][8][9][10] The advantages of low cost production, chemical flexibility, self-assembly process, tunable electronic structure, and long spin lifetime in organic molecules make them viable spacer candidates for a TMR device.…”

“…[11][12][13] Until now, only two-terminal, molecular spin-valve (MSV) junctions have received major attention. [5][6][7][8][9][10][11][12][13][14][15] Achieving additional control of TMR in such a molecular junction by a gate field is the prerequisite for a spin-valve transistor. 16 In this Letter, we predict giant amplification (320%) of TMR by gate field in a molecular spin valve junction, which consists of a Ru-bis-terpyridine (RBT) molecule as a spacer between two ferromagnetic nickel contacts.…”

Spin transport through a junction entirely consisting of molecules from first principles

“…22 Experimentally, the individual Ni/BDT/Ni junctions have been fabricated with MR values from 30% to 150%. 24,25 In this entire molecular junction, the improvement of the MR ratio is significant. With increasing applied voltage, the calculated MR is reduced gradually from the maximum to 153% eventually, at about 1 V. Such behavior is similar to that of a Ni-BDT-Ni junction 11 and conventional magnetic tunnel junctions.…”

Electron Transport Characteristics of the Dimeric 1,4‐Benzenedithiol Junction

“…In the present study, we utilize a molecular tip functionalized with 1,4-benzenedithiol (BDT), the most widely studied molecule with a conjugated structure, [30,[42][43][44][45][46][47][48] to construct a single molecular pair junction and to quantify its conduc-tance using the STM-based current-displacement I(s) method established by Haiss et al [34] Briefly, the BDT tip was initially set very close to, but not in contact with the gold substrate modified by BDT at low coverage. The distance between the tip and sample surface was manipulated by the STM set point current and bias voltage, which could be calibrated (see the Supporting Information).…”