Hard-hard coupling assisted anomalous magnetoresistance effect in amine-ended single-molecule magnetic junction

Abstract

We proposed a single-molecule magnetic junction (SMMJ), composed of a dissociated amine-ended benzene sandwiched between two Co tip-like nanowires. To better simulate the break junction technique for real SMMJs, the first-principles calculation associated with the hard-hard coupling between a amine-linker and Co tip-atom is carried out for SMMJs with mechanical strain and under an external bias. We predict an anomalous magnetoresistance (MR) effect, including strain-induced sign reversal and bias-induced enhancement of the MR value, which is in sharp contrast to the normal MR effect in conventional magnetic tunnel junctions. The underlying mechanism is the interplay between four spin-polarized currents in parallel and anti-parallel magnetic configurations, originated from the pronounced spin-up transmission feature in the parallel case and spiky transmission peaks in other three spin-polarized channels. These intriguing findings may open a new arena in which magnetotransport and hard-hard coupling are closely coupled in SMMJs and can be dually controlled either via mechanical strain or by an external bias.

Manipulation of Giant Field-Like Spin Torque in Amine-Ended Single-Molecule Magnetic Junctions

“…Surprisingly, their magnitudes are in the same order but 2 orders smaller than that of T ⊥ (0) . Thus, we can conclude the striking discovery in T ⊥ ∼ T ⊥ (0) ≫ T ∥ for Co/BDA/Co SMMJ, where the amine linker plays an important role of the ISF effect to create the spin-polarized transmission channels near the Fermi energy, as shown in Figure 3 of ref , and hence further assists the strong IEC via quantum interferences due to the spin-dependent reflections at the Co/N contacts.…”

“…When a BDA molecule is sandwiched between two Co NWs, T ⊥ ( V ) has an even parity with respect to external bias, i.e., T ⊥ V ( V ) ∼ T ⊥ V (− V ), due to the nearly symmetric geometry of Co/BDA/Co SMMJ. Moreover, the amine linker assisted spin-polarized transmission channels near the Fermi energy, as shown in Figure 3 of ref , strengthen the spin selective resonance tunneling processes to cause the failure in the general expression of T ∥ , resulting from the breakdown of sinusoidal angular dependence in T ∥ , as shown in Figure b. This in turns renders the anomalous bias behavior of T ∥ with sign reversal without a corresponding sign reversal of bias.…”

“…Because the strong hard–hard coupling between the amine linker and Co tip atom provides highly spin-polarized transmission channels near the Fermi energy via the hybridization between Co- d and N-p y orbitals, the amine linker plays a significant role in the interfacial spin filter (ISF) layer and hence dominates the spin transport properties between Co NWs (FM) and the central molecule (I). Except for the anomalous bias-induced enhancement of the MR value and the strain-enhanced spin injection, the ISF-induced spin-dependent reflections at the Co/N contacts may enhance the IEC and hence strengthen the FLST effect, which still remains unexplored thus far.…”

Large Magnetoresistance in Fe3O4/4,4′-Bipyridine/Fe3O4 Organic Magnetic Tunnel Junctions

“…However, the left and right electrodes in present OMTJs are obtained by means of mirrors, which exactly have the same left and right spinterfaces. Until now, other results on negative TMR in symmetric OMTJs were related to the inversion of hybrid interfacial states, or the presence of applied bias or strain, ,,,− whereas the anomalous negative TMR in present OMTJs is at equilibrium condition, and it also cannot be ascribed to the inversion of interfacial states since the interfacial Fe A and Fe B keep the original sign of spin polarization. Nevertheless, the hybrid states between organic BP molecule and Fe 3 O 4 cannot be ignored.…”

“…A large amount of effort has been made to improve the TMR value in OMTJs. − A TMR of up to 80% has been observed in single C 60 molecule transistors with ferromagnetic Ni electrodes . In a Ni/hydrogen phthalocyanine (Pc)/Ni magnetic junction, a TMR of ∼60% was measured by the spin-polarized scanning tunneling microscopy .…”