Istituto dei materiali per l'elettronica ed il magnetismo     
Bergenti I., Dediu V., Borgatti F., Riminucci A., Hueso L. H., Casoli F., Zhan Y., Pernechele C., Solzi M. Spin polarised electrodes and interfaces in organic spintronic devices. In: Intermag 2008 (Madrid, Spain, 4-8 maggio 2008).
Applications of organic semiconductors into spintronic domain, motivated by unquestionable advantage of weak spin-orbit coupling and hyperfine interaction, have been recently successfully demonstrated[1]. Magnetoresistive spin valves and magnetic tunnel junction based on archetypal organic materials Alq3 have been experimentally obtained [2,3]. In spite of the different mecha- nism, injection/transport for Spin Valves and tunnelling for magnetic tunnel junction, their per- formances are affected not just by the properties of their constituents but also by their metal/organ- ic interfaces. Investigations on ferromagnet/organic interfaces are crucial in vertical devices, which typically include the deposition of a ferromagnetic contact on top of organic materials. Such dep- osition is by its nature critical: penetration of atoms, formations of complexes and cluster can be expected. Morphology and disorder of ferromagnetic thin films, possible intermixing or interdiffusion at the interface may change the magnetic properties of the FM films and affect the intensity of spin valve effect. For this reason a detailed characterization of ferromagnetic metal/organic semiconductor heterostructures is necessary in order to understand and predict the device behaviour. Hybrid spin valves with highly spin polarized manganite La2/3Sr1/3MnO3 and Cobalt as ferro- magnetic electrodes and Alq3 as organic transport layer have been investigated (for experimental details see [4]). Room temperature operation have been obtained trough the control of interfacial properties and interface engineering. We present a full magnetic and morphological characterization of ferromagnetic films used as elec- trodes in spin valves devices and we correlate the results with the Spin valve device performance. 20 nm thick LSMO epitaxial films present a XMCD signal at room temperature indicating a good surface magnetisation. AFM investigations on 100 nm thick Alq3 films grown on epitaxial LSMO indicate a very smooth surface (rms 1 nm). A template growth of Co layers on top of organic semi- conductor is observed. Magnetic characterization by MOKE and SQUID indicates the presence of a uniaxial anisotropy. X ray magnetic reflectivity indicates that sharp Co/Alq3 interfaces are obtained in presence of a thin AlOx tunnel barrier(fig.1). An intermixing region of 2 nm has been measured. The tunnel bar- rier prevents the degradation of the interface and improves the quality of the SV effect reaching the room temperature operation. [1]Sanvito S. J. Mat. Chem. 17, 4455 (2007) and references therein [2]Xiong, Z.H., Wu, D., Vardeny, Z.V. & Shi, J. Nature 427, 821-824 (2004) [3]Santos, T.S., Lee, J.S., Migdal, P., Lekshmi, I.C., Satpati, B. & Moodera, J.S. Phys. Rev. Lett. 98, 016601 (2007) [4]Hueso, L.E., Riminucci, A., Bergenti, I., Zhan, Y. & Dediu, V. Adv. Mater. 19, 2639-2642 (2007).
Subject Organic Spintronics
Spin-valve effect

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