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Spin-Polarized Light-Emitting Diode Based on an Organic Bipolar Spin Valve

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Science  13 Jul 2012:
Vol. 337, Issue 6091, pp. 204-209
DOI: 10.1126/science.1223444

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  1. Fig. 1

    (A) Spin-OLED device operation under the condition of unbalanced electron-hole space charge limited current (SCLC): (1) OLED with non-FM electrodes; the “recombination” current δI is inversely related to the efficiency of PP formation via the bimolecular recombination coefficient b; also, EL ∝ δI. (2 and 3) OLED with FM electrodes: b becomes magnetic field–dependent via the spin injection of the FM electrodes, giving rise to spin-dependent current and EL. (B) The spin-OLED device structure, where the D-DOO-PPV organic layer thickness is ~25 nm and LiF buffer layer thickness is ~1.5 nm. Here the in-plane magnetic field (black arrow) causes the FM magnetizations (red arrows) to align parallel to each other. The EL emission (wavy red line) is collected through the Co/Al thin electrode. (C) The device I-V and EL-V characteristics; the EL onset is at Vo ≈ 3.5 V. Inset: D-DOO-PPV polymer chemical structure.

  2. Fig. 2

    Magneto-electroluminescence (MEL) response of a spin-OLED device. (A) Obtained MELEX(B) response for up (red) and down (blue) B-sweeps, measured at Vb = 4.5 V and T = 10 K, for device A (d = 25 nm, d′ = 1.5 nm). The black dashed line describes the nonhysteretic, intrinsic MEL background response for an up-sweep. The horizontal arrows mark the relative electrode magnetization directions. (B) The net MELSV(B) response after subtraction of the background MEL from the measured MEL response shown in (A). (C) The bias voltage dependence of the maximum MELSV value. (D) Magneto-optic Kerr effect (MOKE) measurements of the LSMO and Co/LiF electrodes at 10 K that show coercive fields Bc(FM1) ≈ 5 mT and Bc(FM2) ≈ 35 mT, respectively.

  3. Fig. 3

    (A) The maximum MELSV response of spin-OLED devices at various polymer thicknesses d and LiF buffer layer thicknesses d′ of 0.8 nm (red squares) and 1.5 nm (blue squares), measured at T = 10 K and Vb = 4.5 V. (B) The optimum MELSV(B) response of ~1.1% measured for a device with d = 18 nm and d′ = 0.8 nm. (C) The maximum MELSV(T) response at Vb = 5 V (red squares) for a spin-OLED device with d = 25 nm and d′ = 1.5 nm; the LSMO bulk magnetization versus T measured by superconducting quantum interference device (SQUID) (blue stars); and its fit using the Brillouin function BJ(T/Tc) with J = 5/2 and Tc = 307 K (blue line). (D to G) MEL(B) response at selected temperatures.

  4. Fig. 4

    Magnetoconductance (MC) response of bipolar and homopolar OSV devices based on D-DOO-PPV and measured at 10 K (d = 25 nm, d′ = 1.5 nm). (A and B) MC(B) response of bipolar OSV device measured at Vb = 0.6 V and 5 V, respectively, at positive (red) and negative (blue) B-sweeps. (C) Maximum MCSV value versus Vb for the bipolar device. (D and E) MC(B) response of homopolar OSV device measured at Vb = 1 V and 3.5 V, respectively, at positive (red) and negative (blue) B-sweeps. (F) Maximum MCSV value versus Vb for the homopolar device.

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