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| 2. |
- Bloom, F. L., et al.
(author)
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Correspondence of the sign change in organic magnetoresistance with the onset of bipolar charge transport
- 2008
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In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 93:26
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Journal article (peer-reviewed)abstract
- In this work we examine the transition between positive and negative organic magnetoresistance in poly[2-methoxy-5-(3(), 7()-dimethyloctyloxy)-p-phenylenevinylene] in order to understand how different regimes of charge transport affect the organic magnetoresistance effect. To characterize the charge transport in these devices we measured the current, low frequency differential capacitance, and electroluminescence efficiency as a function of voltage. These measurements show that the sign change of the magnetoresistance corresponds with a change from a unipolar diffusive transport below the built in voltage (V(bi)) to a regime of bipolar drift transport above V(bi).
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| 3. |
- Bloom, F. L., et al.
(author)
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Separating positive and negative magnetoresistance in organic semiconductor devices
- 2007
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 99:25
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Journal article (peer-reviewed)abstract
- We study the transition between positive and negative organic magnetoresistance (OMAR) in tris-(8 hydroxyquinoline) aluminium (Alq(3)), in order to identify the elementary mechanisms governing this phenomenon. We show how the sign of OMAR changes as function of the applied voltage and temperature. The transition from negative to positive magnetoresistance (MR) is found to be accompanied by an increase in slope of log(I) versus log(V). ac admittance measurements show this transition coincides with the onset of minority charge (hole) injection in the device. All these observations are consistent with two simultaneous contributions with opposite sign of MR, which may be assigned to holes and electrons having different magnetic field responses.
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| 4. |
- Bloom, F. L., et al.
(author)
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Sign Inversion of Magnetoresistance in Space-Charge Limited Organic Devices
- 2009
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 103:6
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Journal article (peer-reviewed)abstract
- In this Letter, we explain the puzzling sign change of organic magnetoresistance in space-charge limited devices by device physics. We prove analytically and numerically that in the case of bipolar conduction with an Ohmic majority carrier and an injection limited minority carrier contact, a decrease in minority carrier mobility may give rise to an increase in the device current. It is shown that when the magnetic field acts to decrease the mobility of both carriers, a sign change in the magnetoconductivity as a function of applied bias may result. This behavior is in agreement with experimental observations.
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| 5. |
- Boulle, Olivier, et al.
(author)
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Non-adiabatic spin transfer torque in high anisotropic magnetic nanowires with narrow domain walls
- 2008
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:21, s. 1-4
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Journal article (peer-reviewed)abstract
- Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized (Pt/Co)3/Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism.
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| 8. |
- Van Kampen, M., et al.
(author)
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On the realization of artificial XY spin chains
- 2005
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In: Journal of Physics. - 0953-8984 .- 1361-648X. ; 17:2, s. L27-L33
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Journal article (peer-reviewed)abstract
- Spin chains are the most elementary entities in the study of magnetic ordering behavior. The authors describe a route toward the realization of artificial XY spin chains. Using thin-film deposition and e-beam lithog., 300 and 550 nm diam. pillars consisting of alternating disks of permalloy and Al2O3 were made. Shape anisotropy forces the magnetization in plane, creating a chain of two-dimensional magnetic moments →i. The disks couple to each other by their dipolar stray fields, resulting in an interaction Jij→i·→j, with Jij the coupling between disks i and j. This form closely resembles a chain of xy spins, coupled by effective interactions Jij. The authors present a magnetic characterization of the pillars, and compare the results with model calcns. Also, spin dynamics and ordering phenomena are addressed.
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