to be as the channel materials of FETs. [9] Recently, the HfSe 2 has been predicted to possess much higher carrier mobility above 3000 cm 2 (V s) −1 surpassing that of Si more than double so that scientists are attracted to fall in this field. [9] The backgated FETs of exfoliated multilayer HfSe 2 with a high on/off current ratio of >7.5 × 10 6 on SiO 2 /Si substrate were initially fabricated; nevertheless, the extraced carrier mobilities are lower than 1 cm 2 (V s) −1 . [10] Then the top-gated multilayer HfSe 2 FETs with high κ dielectrics grown by atomic layer deposition were demonstrated this year, but the multilayer HfSe 2 was still obtained by mechanical exfoliation and the carrier mobilities of devices were only enhanced to ≈4 cm 2 (V s) −1 . [11] Moreover, the phototransistors
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.
We employ the first-principles calculation with nonequilibrium Green's function method to comprehensively investigate the crucial role of interfacial geometry in spin transport properties of Co/1,4-benzenediamine (BDA)/Co single-molecule magnetic junctions (SMMJs). Two bonding mechanisms are proposed for the hard−hard Co−N coupling: (1) the covalent bonding between the H-dissociated amine linker and spinpolarized Co apex atoms and (2) the dative interaction between the H-non-dissociated (denoted by +H) amine linker and Co apex atoms. The former covalent contact dominates the π-resonance interfacial spin selection that can be well preserved in Hdissociated cases regardless of the choice of top, bridge, and hollow contact sites. From our detailed analyses of spin-polarized transmission spectra, local density of states, and molecular density of states, the underlying mechanism is that the strong hybridization between Co-d, N-p y , and the π-orbital of the phenyl ring in dissociated cases renders the 2-fold HOMO (4-fold LUMO) of the central molecule closer to the Fermi energy. In contrast, the enlarged Co−N bond length of the latter dative contact in the H-non-dissociated case not only destroys the spinterface coupling but also blocks the spin injection. This theoretical work may provide vital and practical insights to illustrate the spin transport property in real amine-ended SMMJs since the contact geometries and interfacial bond mechanisms remain unclear during the breaking junction technique.
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