Abstract
Organic materials are attractive for building spintronics devices owing to their expected long spin lifetimes. Moreover, the ability to control their properties by changing their composition and molecular structure makes them easier to tailor to given tasks than inorganic materials. However, most studies of candidate organic spintronics materials focus on their bulk spin transport characteristics. Here we investigate the equally important process of spin injection and how it is influenced by interface coupling in the prototype organic semiconductor, Alq3. We fabricate nanometre-scale (La,Sr)MnO3/Alq3/Co magnetic tunnel junctions that exhibit a magnetoresistive response of up to 300%. Furthermore, we develop a spin transport model that describes the role of interfacial spin-dependent metal/molecule hybridization on the effective polarization allowing enhancement and even sign reversal of injected spins. We expect such insights to lead towards the molecular-level engineering of metal/organic interfaces to tailor spin injection and bring new electrical functionalities to spintronics devices.
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References
Fert, A. Nobel lecture: Origin, development, and future of spintronics. Rev. Mod. Phys. 80, 1517–1530 (2008).
Cuniberti, G., Richter, K. & Fagas, G. (eds) in Introducing Molecular Electronics Vol. 680 (Springer, 2005).
Dediu, V., Hueso, L., Bergenti, I. & Taliani, C. Spin routes in organic semiconductors. Nature Mater. 8, 707–716 (2009).
Sanvito, S. & Rocha, A. R. Molecular spintronics: The art of driving spin through molecules. J. Comput. Theor. Nanosci. 3, 624–642 (2006).
Drew, A. J. et al. Direct measurement of the electronic spin diffusion length in a fully functional organic spin value by low-energy muon spin rotation. Nature Mater. 8, 109–114 (2009).
Cinchetti, M. et al. Determination of spin injection and transport in a ferromagnet/organic semiconductor heterojunction by two-photon photoemission. Nature Mater. 8, 115–119 (2009).
Dediu, V., Murgia, M., Matacotta, F. C., Taliani, C. & Barbanera, S. Room temperature spin polarized injection in organic semiconductor. Solid State Commun. 122, 181–184 (2002).
Xiong, Z. H., Wu, D. & Vardeny, Z. V. Giant magnetoresistance in organic spin-valves. Nature 427, 821–824 (2004).
Majumdar, S., Majumdar, H. S., Laiho, R. & Osterbacka, R. Comparing small molecules and polymer for future organic spin-valves. J. Alloys Compounds 423, 169–171 (2006).
Wang, F. J., Yang, C. G., Vardeny, Z. V. & Li, X. Spin response in organic spin valves based on La2/3Sr1/3MnO3 electrodes. Phys. Rev. B 75, 245324 (2007).
Xu, W. et al. Tunneling magnetoresistance observed in La2/3Sr1/3MnO3/organic molecule/Co junctions. Appl. Phys. Lett. 90, 072506 (2007).
Hueso, L. E., Bergenti, I., Riminucci, A., Zhan, Y. Q. & Dediu, V. Multipurpose magnetic organic hybrid devices. Adv. Mater. 19, 2639–2642 (2007).
Dediu, V. et al. Room-temperature spintronic effects in Alq3-based hybrid devices. Phys. Rev. B 78, 115203 (2008).
Vinzelberg, H. et al. Low temperature tunneling magnetoresistance on (La,Sr)MnO3/Co junctions with organic spacer layers. J. Appl. Phys. 103, 093720 (2008).
Santos, T. S. et al. Room-temperature tunnel magnetoresistance and spin-polarized tunneling through an organic semiconductor barrier. Phys. Rev. Lett. 98, 016601 (2007).
Why going organic is good Nature Mater. 8, 691 (2009). 10.1038/nmat2517
Sakaguchi, H. et al. Determination of performance on tunnel conduction through molecular wire using a conductive atomic force microscope. Appl. Phys. Lett. 79, 3708–3710 (2001).
Matsumoto, R. et al. Oscillation of giant tunneling magnetoresistance with respect to tunneling barrier thickness in fully epitaxial Fe/MgO/Fe magnetic tunnel junctions. Appl. Phys. Lett. 90, 252506 (2007).
Zhan, Y. Q. et al. Alignment of energy levels at the Alq3/La0.7Sr0.3MnO3 interface for organic spintronic devices. Phys. Rev. B 76, 045406 (2007).
Akkerman, H. B. et al. Electron tunneling through alkanedithiol self-assembled monolayers in large-area molecular junctions. Proc. Natl Acad. Sci. USA 104, 11161–11166 (2007).
Vàzquez, H., Flores, F. & Kahn, A. Induced density of states model for weakly interacting organic semiconductor interfaces. Org. Electron. 8, 241–248 (2007).
Bratkovsky, A. M. Assisted tunneling in ferromagnetic junctions and half-metallic oxides. Appl. Phys. Lett. 72, 2334–2336 (1998).
Bernand-Mantel, A. et al. Evidence for spin injection in a single metallic nanoparticle: A step towards nanospintronics. Appl. Phys. Lett. 89, 062502 (2006).
Bowen, M. et al. Observation of Fowler–Nordheim hole regime across an electron tunnel junction due to total symmetry filtering. Phys. Rev. B 73, 140408(R) (2006).
Mattana, R. et al. Chemical profile and magnetoresistance of Ga1−xMnxAs/GaAs/AlAs/GaAs/Ga1−xMnxAs tunnel junctions. Phys. Rev. B 71, 075206 (2005).
Wang, W. & Richter, C. A. Spin-polarized inelastic electron tunneling spectroscopy of a molecular magnetic tunnel junction. Appl. Phys. Lett. 89, 153105 (2006).
Tautz, F. S. et al. Strong electron–phonon coupling at a metal/organic interface: PTCDA/Ag(111). Phys. Rev. B 65, 125405 (2002).
DeTeresa, J. M. et al. Role of the metal–oxide interface in determining the spin polarization of magnetic tunnel junction. Science 286, 507–509 (1999).
Meservey, R. & Tedrow, P. M. Spin-polarized electron-tunneling. Phys. Rep. 238, 173–243 (1994).
Velev, J. P., Dowben, P. A., Tsymbal, E. Y., Jenkins, S. J. & Caruso, A. N. Interface effects in spin-polarized metal/insulator layered structures. Surf. Sci. Rep. 63, 400–425 (2008).
Caruso, A. N., Schulz, D. L. & Dowben, P. A. Metal hybridization and electronic structure of tris(8-hydroxyquinolato) aluminum (Alq(3)). Chem. Phys. Lett. 413, 321–325 (2005).
Baldo, M. A. & Forrest, S. R. Interface-limited injection in amorphous organic semiconductors. Phys. Rev. B 64, 085201 (2001).
Bässler, H. Charge transport in disordered organic photoconductors. Phys. Status Solidi B 175, 15–56 (1993).
Nitzan, A. & Ratner, M. Electron transport in molecular wire junctions. Science 300, 1384–1389 (2003).
Mujica, V., Kemp, M. & Ratner, M. Electron conduction in molecular wires I A scattering formalism. J. Chem. Phys. 101, 6849–6855 (1994).
Vàzquez, H. et al. Dipole formation at metal/PTCDA interfaces: Role of the charge neutrality level. Europhys. Lett. 65, 802–808 (2004).
Tsymbal, E. Y., Sokolov, A., Sabirianov, I. F. & Doudin, B. Resonant inversion of tunneling magnetoresistance. Phys. Rev. Lett. 90, 186602 (2003).
Garcia, V. et al. Resonant tunneling magnetoresistance in MnAs/III–V/MnAs junctions. Phys. Rev. B 72, 081303 (2005).
Reily Rocha, A. & Sanvito, S. Resonant magnetoresistance in organic spin valves. J. Appl. Phys. 101, 09B102 (2007).
Bouzehouane, K. et al. Nanolithography based on real-time electrically controlled indentation with an atomic force microscope for nanocontact elaboration. Nano Lett. 3, 1599–1602 (2003).
Acknowledgements
We thank C. Carretero and R. Guillemet for technical assistance. We also thank S. Tatay-Aguilar, A. Riminucci, M. Prezioso, A-A. Drillien and E. Girard for fruitful discussions. We acknowledge the financial support from EU-FP6-STRP under Grant No. 033370 OFSPIN, French ANR-PNANO under grant SPINORGA and ALICANTE, RTRA Triangle de la Physique and C’Nano Ile de France.
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C.B., R.M. and P.S. carried out the project, including experimental work, data analysis, model conception and development and writing of the paper. P.G., L.H., I.B. and V.D. grew, characterized and provided the LSMO/Alq3 bilayers. K.B., S.F. and C.D. contributed to the nanolithography and final electrode growth for the samples. K.B., F.P. and A.F. participated in general discussions and writing of the paper.
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Barraud, C., Seneor, P., Mattana, R. et al. Unravelling the role of the interface for spin injection into organic semiconductors. Nature Phys 6, 615–620 (2010). https://doi.org/10.1038/nphys1688
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DOI: https://doi.org/10.1038/nphys1688
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