New method of spin injection into organic semiconductors using spin filtering tunnel barriers

In an organic light emitting diode, injection of spin-polarized current can be expected to influence the light emission. For the emission to occur, the bias voltage must exceed the device turn-on voltage. However in magnetic junctions with conventional ferromagnetic electrodes, the magnetoresistance decreases as bias increases. This response limits the use of such ferromagnets for spin injection in organic light emitting diodes where high bias is needed. A way out of this limitation is shown here, by utilizing the spin-filter phenomenon to generate current spin polarization, and inject into an organic semiconductor. Europium sulfide was used as the spin-filter layer with rubrene as the barrier to form a quasi-magnetic junction. The junctions showed magnetoresistance which increased as bias voltage was increased, with a high value of 6% at 1.8 V. These results show the potential to use spin-filter systems for investigating electroluminescence in organic light emitting diodes with spin-polarized electrons. Ferrite compound spin-filters with Curie temperature much above room temperature are a potential class of materials to realize room temperature spintronics devices.

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► A new method to inject spins in organic semiconductor using the spin filter phenomenon is demonstrated.
► The spin-filter, EuS, acts as a tunnel barrier with spin-split conduction band to form quasi magnetic junction devices.
► Magnetoresistance (MR) of 6% is reported at high voltage bias ∼ 1.8 V.
► The devices exhibit an unconventional bias dependence of MR: MR increased with applied voltage.