Research On The Organic Magnetoresistance Effect

ABSTRACT:Spin electronics aims to use the electron spin rather than the traditional electronic charge to research new generation technology of electronic products. It is a very important aspect of condensed matter and material physics. And as a branch of spin electronics, organic magnetoresistance effect is now attracting more and more interesting.In this paper we fabricate traditional organic sandwich devices, by using different active layer material, and inserting charge carrier transport layer, we observe the organic magnctoresistance effect(OMR) of such devices and analyse the impact of different material and charge carrier transport layers, and analyse the excitonic model and triplets—paramagnetic centers interaction as well. Specifically, it is mainly includes the following content:Firstly, we fabricated an OLED device which structure was ITO/PEDOT/MEH-PPV/Al, and found the relationship between organic magnetoresistance and the device voltage, as well as the magnetic field. The magnetic conductance(MC) of the device increased at first and decline with a larger voltage(～above 3 V) and the MC value was about 15%. When we used P3HT instead of MEH-PPV, we compare and analyse the organic magnetoresistance effect of both devices. To account for the different results of such two devices, we consider that different electron mobility of MEH-PPV and P3HT results different rates of exciton formation of the devices at low voltage.Secondly, a device ITO/PEDOT/Alq3/LiF:Al was fabricated and characterized. We got the curve of magnetoresistance and the voltage, as well as the magnetic field. By inserting a layer of BCP or C6o between active layer Alq3 and the cathode Al, we found the curve changed and attribute this to the change of exciton formation in the devices. The MC value of the device of 6 V increased from 9% to 14% at 120 mT with BCP. The curves of magnetoresistance and the voltage of both devices which used polymer or organic molecule as the active layer appeared more than one extremes.Finally, we used the non-luminous material C60 as the active layer and fabricated a device of ITO/PEDOT/C60/Al. The organic magnetoresistance effect was still observed and there was a contradiction between Desai's conclusion that OMR only occurs in OLEDs and our experimental data. We believe that the organic magnetoresistance effect is based on several mechanisms. At low voltage the bipolaron model can explain the experiments and with the increasingly voltage, excitonic model is dominant. So the mechanism of OMR is complex.