Electrical and Magnetic switching in Alq3 and Pentacene Organic Spin Valves

Valentin A. Dediu 1Mirko Prezioso 1Alberto Riminucci 1Patrizio Graziosi 1David Brunel 1Ilaria Bergenti 1Carol Newby 

1. Istituto per lo Studio dei Materiali Nanostrutturati (ISMN-CNR), Gobetti 101, Bologna 40129, Italy

In this work we show the magnetoresisitve and electrical properties of Alq3 based (La0.7Sr0.3MnO3(LSMO)/Alq3/AlOx/Co) and Pentacene based (La0.7Sr0.3MnO3/Alq3/Pentacene/AlOx/Co) organic spin valves (OSV).

Alq3 is one of the most studied organic semiconductors (OS), both for organic LEDs (OLED) applications and, more recently, for organic spintronic devices. Pentacene instead is the main OS for organic FETs (OFETs) because of its high mobility. Therefore, these two organic materials are very important for spintronic devices too.

When measuring the Alq3 based OSV with a -100 mV applied bias, we observed the existence of two resistive states, one high resistance state (about 4.2 MΩ) that showed no spin valve effect, and a low resistance state (about 560 kΩ) which showed a spin valve effect of up to 22% at 100 K. The high resistance state was induced by the application of a -1.5 V bias to the LSMO electrode prior to the measurement, whereas we applied a positive bias greater than 2 V to drive the device in the low resistance state. The figures show the magnetoresistance of a OSV in its low resistance (top) and high resistance (bottom) state. Above a positive bias threshold, the spin valve effect increased as the voltage applied before the measurement was increased.

sp68_2MR_100K_onstate.gif - 8.11 Kb sp68_2MR_100K_offstate.gif - 12.17 Kb

Very interesting results were also obtained with the Pentacene based spin valves. In this case the IVs of the devices showed a switching in the differential resistance at threshold voltage, which increased with temperature. They showed a spin valve MR when the absolute value of the applied voltage was below the threshold. When the absolute value of the applied voltage was greater than the threshold, the spin valve MR was replaced by a negative magnetoresistance.

These results show joint electrical and magnetic effects, which is very interesting both from a fundamental and from an applicative point of view.

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Presentation: Poster at E-MRS Fall Meeting 2009, Symposium E, by Alberto Riminucci
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-22 20:49
Revised:   2009-09-04 13:50
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