Study On The Configuration Effect Of Spin-polarized Interface At The Molecular/ferromagnetic Interface

In the past decades, as a newly-developing subject, spintronics has developed quickly and attracted extensive attention. As an important part of spintronics, organic spintronics, which is based on organic materials, focuses on the study of spin injection, spin detection, spin-dependent transport and control. Compared with inorganic spintronics, organic spintronics has enormous advantage. Firstly, organic material has weak spin-orbit and hyperfine interaction, large relaxation time, which is benefit for spin storage. Secondly, organic material is soft, so taking shape with ferromagnetic material is easy without the problem of interfacial resistance matching just as inorganic material, which is beneficial for the spin injection. Besides, organic material is light-weight, low-cost, more-kinds and easily mass-produced. Therefore, organic spintronics causes more attention.At present, based on the study about organic spintronics devices on experiment and theory, researchers divide devices into two kinds: one is ferromagnet/organic molecule/ferromagnet organic spin valve, which is used for the study of resistance by changing the magnetic moment of electrode. The other is made from organic magnetic molecule, this kind of device utilizes its spin correlation to achieve spin function. For the organic spin device, the spin polarization of interface between organic molecule and ferromagnetic electrode is especially important, which is the precondition of achieving spin injection and spin transport. Organic/ferromagnetic interface is more complex than inorganic device, that is because organic matter can form chemical bonding with electrode, and spin hybridization will exist on interface, which results in the difference of spin polarization on interface or in interior. Meanwhile, the complexity of interfacial configuration will further influence interfacial orbital hybridization and spin polarization. Present study on experiment also indicate that magnetoresistance effect in same configuration devices has essential difference, where the polytrope of organic/ferromagnetic interface may play an important role. Thus, understanding the impact of organic/ferromagnetic interfacial configuration acting on interfacial spin polarization in organic devices is essential, which is the precondition of understanding the property of spin transport and magnetoresistance and so on.In this paper, we mainly study ferromagnetic electrode/organic molecule heterostructure. Based on the quantum chemical ab-initio theory, we discuss the influence of interfacial contact configuration and interfacial angle between molecule and electrode to spin polarization systematacially.Results of our paper are given as follows:1.Adopting benzene-dithiolate molecule and nickel electrode, we study the spin polarization when molecule is adsorbed vertically on the surface of electrode. By calculating interfacial spin polarization in hollow, bridge and top three different contact configurations, we find that interfacial spin polarization is influenced deeply by different contact configurations, even the sign of spin polarization may vary from positive to negative when the contact configuration is changed. By analyzing the projected density of states, an interfacial orbital hybridization between the 3d orbital of the electrode atom and the sp3 hybridized orbital of the contact site atom in molecule is observed. We also simulate the interfacial adsorption in mechanically controllable break junction experiment and calculate its interfacial spin polarization. The magnetoresistance obtained from Julliere model is consistent with experimental measurement.2.Considering the practical truth of molecule spin valves, we study the interfacial spin polarization when molecule is adsorbed on the surface of ferromagnetic electrode by different angles. We find that in the case of flat adsorption, an interfacial orbital hybridization occurs between the 3d orbital of the electrode atom and not only the pz orbital of the C atom but also the sp3 hybridized orbital of S atom, while in vertical adsorption the orbital hybridization between the 3d orbital of the electrode atom and the sp3 hybridized orbital of S atom mainly causes the interfacial spin polarization. When an angle exists between molecule and electrode, pz-d orbital hybridization caused by C and Ni atoms and sp3-d orbital hybridization provided by S and Ni atoms may exist simultaneously. With the increase of angle, pz-d orbital hybridization decreases rapidly, which results in the prompt diminution of pz orbital spin polarization of C atom with the angle increasing, while sp3-d orbital hybridization has tiny dependence on angle, thus in large angles spin polarization of terminal S atom has major contribution to the spin polarization on Fermi level. Researches show that value and sign of interfacial spin polarization can be changed by changing the angle between molecule and surface of electrode.