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Giant magnetoresistance in organic spin-valves


A spin valve is a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance1 and tunnelling magnetoresistance2 in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics3—‘spintronics’. Intense research efforts are now devoted to extending these spin-dependent effects to semiconductor materials. But while there have been noteworthy advances in spin injection and detection using inorganic semiconductors4,5,6, spin-valve devices with semiconducting spacers have not yet been demonstrated. π-conjugated organic semiconductors may offer a promising alternative approach to semiconductor spintronics, by virtue of their relatively strong electron–phonon coupling7 and large spin coherence8. Here we report the injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.

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Figure 1: The structure and transport properties of the fabricated organic spin-valve devices.
Figure 2: The magneto-transport response of the OSE spin-valve devices.
Figure 3: Bias voltage dependence.
Figure 4: Temperature dependence.

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We thank X.G. Li at the University of Science and Technology of China for providing the LSMO films and C. Taliani, V. Dediu, V. Burtman and D. Smith for discussions. We also thank F. J. Wang, C. G. Yang, C. Z. Liu and M. DeLong for assistance with the measurements. This work was supported in part by the National Science Foundation, Petroleum Research Foundation, DARPA, and the Department of Energy.

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Correspondence to Jing Shi.

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Supplementary information

Supplementary Figure 1

GMR of LSMO/ Alq3/Co spin-valve devices of various spacer thicknesses, d, measured at 11 K. (PDF 75 kb)

Supplementary Figure 2

Room temperature external quantum efficiency of a control light-emitting ITO/Alq3/Co device with d = 160 nm. Both current-voltage, I(V), and electroluminescence intensity, EL(V), responses of this device are shown in the inset. (PDF 54 kb)

Supplementary Figure 3

The spin ½ resonance measured using the conductivity-detected magnetic resonance technique on a control ITO/Alq3/Co device. A relatively strong resonance at g ~ 2 shows that spin ½ carriers are indeed injected into the OSE spacer. (PDF 53 kb)

Supplementary Figure 4

The MR response of the bare Co electrode measured at bias voltage of 0.1 mV and 11 K. (PDF 57 kb)

Supplementary Figure 5

The MR response of the bare LSMO electrode measured at bias voltage of 5 mV and 11 K. (PDF 62 kb)

Supplementary Figure 6

The MR response of a control device ITO/Alq3/Co measured at bias voltage of 10 mV and 11 K. (PDF 58 kb)

Supplementary Figure 7

The I(V) of the ITO/parylene/ Co device measured at room temperature. (PDF 42 kb)

Supplementary Information and Figure Legends

This shows in more detail, the spin-valve giant magnetoresistance (GMR) measurements on devices with a variety of organic semiconductor (OSE) spacer thicknesses, in addition to those shown in Fig. 2a. Also shown are a number of magnetoresistance (MR) measurements on several devices that were fabricated specifically for the purpose of serving for control measurements in comparison with the real spin-valve devices. (DOC 31 kb)

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Xiong, Z., Wu, D., Valy Vardeny, Z. et al. Giant magnetoresistance in organic spin-valves. Nature 427, 821–824 (2004).

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