Organic magnetoresistance (OMAR) is a universal magnetic field effect in organic semiconductor based devices with non-magnetic electrode where the device show a substantial change in electrical current under low magnetic field of few milliTeslas.¹ At room temperature, the maximum change in current observed is of the order of 15 - 20% for most organic small molecules and polymers having hydrogen molecules in their side chains and this effect is the highest reported so far for any non-magnetic material. This universality of OMAR, apart from being very intriguing from the physical point of view, gives rise to tremendous prospect for application of these devices in magnetic sensors and also magnetically controlled opto-electronic devices.

            We have made inkjet printed organic diodes on flexible plastic substrates (PET-505) and thoroughly investigated their magnetoresistance (MR) properties. The bottom electrode was evaporated or sputtered and the semiconductor and the top electrodes were inkjetted from a Dimatix^TM printer. Preliminary results show that depending on the materials and operating conditions of the device both increase or decrease in electrical current (i.e. negative or positive MR) can be achieved from these diode devices under a magnetic field which can be used for magnetic field sensing purposes. A detailed discussion of different physical aspects of OMAR will be presented and a comparison will be made between results from the spin-coated and ink-jet printed devices to understand the role of different fabrication techniques on the device properties and also the prospect of roll to roll fabricated magnetic sensors in near future.

References:

¹       Ö. Mermer, G. Veeraraghavan, T. L. Francis, Y. Sheng, D. T. Nyugen, M. Wohlgenannt, A. Köhler, M. K. Al-Suti, and M. S. Khan, Phys. Rev. B 72, 205202 (2005).

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