Spin-dependent transport in C60-based vertical transistors

A. BEDOYA-PINTO; M. GOBBI; F. GOLMAR; R. LLOPIS; F. CASANOVA; L. HUESO

Peníscola, Castelló

Encuentro; IV European School on Molecular Nanoscience; 2011

The use of the electron spin as an additional degree of freedom has been fundamental for the development of novel information processing and logic devices. The reading heads of the hard disk drives, which are our daily workhorse for data storage, are based on spin effects such as the giant- and tunnel magnetoresistance (GMRTMR) [1,2]. While there has been an extraordinary success in fabricating reliable magnetic tunnel junctions which are already irreplaceable elements in information technology, more efforts are still needed to expand these spintronic effects to other materials with different functional properties, which would then result in a more complex generation of spintronic devices. In this respect, organic semiconductors (OS) have emerged as a promising material class for spintronic applications [3], mainly due to their weak spin relaxation mechanisms which result in long spin lifetimes [4]. The sucessful injection of spin-polarized electrons in organic semiconductors might thus lead to the achievement of coherent spin transport and manipulation over longer distances than the sub-nm scale, in a material class with unique electronic, optical and mechanical properties. In this work, we report room-temperature spin transport of C60-based spin valves. Significant magnetoresistance (MR) values for different thicknesses of the C60 interlayer (up to 30 nm) have been achieved in a vertical spin valve geometry. This demonstrates coherent spin transport through the C60 molecules, where the transport of the spin-polarized electrons is found to be consistent with a multi-step tunnelling mechanism [5]. Furthermore, preliminary results of C60-based hot-electron transistor devices will be presented. A large (88%) room-temperature magnetoresistance is found in Al/Al203/Co/Cu/Py/C60/Al spin-valve vertical transistors. The MR-effect shows a strong dependence on the bias voltage at the emitter, the latter corresponding to the energy of the injected hot-electrons. The spin-dependent attenuation of hot electrons is suggested to be responsible for the observation of such a large signal. [1] M. N. Baibich, J. M. Broto, A. Fert, F. Nguyen van Dau, F. Petroff, Physical Review Letters, 1988, 61, 2472 [2] J. S. Moodera, L. R. Kinder, T. M. Wong, R. Meservey, Physical Review Letters, 1995, 74, 3273 [3] V. Dediu, L. E. Hueso, I. Bergenti, C. Taliani, Nature Materials, 2009, 8, 707 [4] D. R. McCarney, H. A. Seipel, S. Y. Paik, M. J. Walter, N. J. Borys, J. M. Lupton, C. Boehme, Nature Materials 2008, 7, 723 [5] M. Gobbi, F. Golmar, R. Llopis, F. Casanova, L. E. Hueso, Advanced Materials, 2011, 23, 1609