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Separating positive and negative magnetoresistance in organic semiconductor devices
F L Bloom1, W Wagemans, M Kemerink
1Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. f.l.bloom@tue.nl
Physical Review Letters
|February 1, 2008
Summary
Researchers investigated the sign change in organic magnetoresistance (OMAR) in tris-(8 hydroxyquinoline) aluminium (Alq3) devices. The study reveals this transition is linked to minority charge injection and differing magnetic responses of electrons and holes.
Area of Science:
- Organic electronics
- Condensed matter physics
- Materials science
Background:
- Organic magnetoresistance (OMAR) is a phenomenon where the resistance of an organic material changes in response to a magnetic field.
- Understanding the mechanisms behind OMAR is crucial for developing novel spintronic devices.
Purpose of the Study:
- To investigate the transition between positive and negative OMAR in tris-(8 hydroxyquinoline) aluminium (Alq3).
- To identify the fundamental mechanisms governing the sign change of OMAR.
- To correlate OMAR behavior with charge injection properties and device characteristics.
Main Methods:
- Studied the effect of applied voltage and temperature on OMAR in Alq3 devices.
- Analyzed the current-voltage (I-V) characteristics, specifically the slope of log(I) versus log(V).
- Performed AC admittance measurements to probe charge injection dynamics.
Main Results:
- Observed a clear transition in the sign of OMAR as a function of applied voltage and temperature.
- The transition from negative to positive magnetoresistance correlated with an increased slope in log(I) vs. log(V) plots.
- AC admittance measurements indicated the onset of minority charge (hole) injection at the transition point.
Conclusions:
- The observed OMAR sign transition is explained by the coexistence of two contributions with opposite magnetoresistance signs.
- These contributions are attributed to electrons and holes, which exhibit distinct responses to magnetic fields.
- Minority charge injection plays a critical role in modulating the OMAR behavior in Alq3 devices.
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