Room-Temperature Spin Transport in C60-Based Spin Valves

M. GOBBI; F. GOLMAR; R. LLOPIS; F. CASANOVA; L. HUESO

ADVANCED MATERIALS

WILEY-V C H VERLAG GMBH

Año: 2011 vol. 23 p. 1609 - 1613

0935-9648

Spintronics, or the possibility of performing electronics with the spin of the electron, has been fundamental for the exponential growth of digital data storage which has occurred in the last decades. Indeed, hard-disk drives read-heads are the maximum exponent of what is currently being called first- generation spintronic devices. Current read-heads, although technologically very complex, are scientifically based simply on the tunnel magnetoresistance effect (TMR; magnetoresistance being the change in electrical resistance of a device under the application of an external magnetic field). A tunnel magneto- resistive vertical spin valve is composed of two ferromagnetic layers separated by a thin (around 1 nm) insulating layer, and the resistance of the structure can be switched between two different values upon the application of a magnetic field capable of rotating the magnetization vector of the ferromagnetic layers from parallel to antiparallel.[1] For the eventual success of a second-generation of spintronic devices, more complex mechanisms than the nanometre-distance spin transport in metallic or insulating materials have to be obtained. In particular, coherent spin transport at distances above a few nm and spin manipulation are unavoidable requirements for the production of sophisticated prototypes of, for example, spin transistors or spin light-emitting diodes.[2,3] Organic semiconductors (OS) have emerged as promising materials for advanced spintronics applications. Their spin relaxation mechanisms, mainly represented by spin orbit interaction and hyperfine interaction with protons,[4] are very small, and long spin lifetimes have been consistently detected.[5] Moreover, in spite of the relatively low carrier mobility of these materials, organic vertical spin valves with semiconducting channels thicker than 100 nm have been demonstrated.[6–11] In parallel, OS ultrathin layers perform successfully as spin tunnel junctions, and extremely high (>300%) magnetoresistance (MR) values have been obtained at low temperatures.[12] Regarding possible applications of spin transport in OS, a basic operational requirement is the room temperature (RT) operation of the devices. So far, only organic spin tunnel junctions have shown any significant MR effect at RT.[13–17] By contrast, most devices employing thicker organic layer (>15 nm) show a clear decay of the MR well below RT.[6–11,18]