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Experimental Tests of Possible Mechanisms for the Organic Magnetoresistive Effect

Published online by Cambridge University Press:  26 February 2011

Tho Duc Nguyen ,
James Rybicki ,
Yugang Sheng  and
Markus Wohlgenannt
Tho Duc Nguyen
Affiliation:
emailtho01@yahoo.com, The University of Iowa, Physics and Astronomy, 203 Van Allen Hall, Iowa city, IA, 52242, United States, 319 353 4480
James Rybicki
Affiliation:
jamesrybicki@gmail.com, The University of Iowa, Physics and Astronomy, 188 IATL, Iowa city, IA, 52242, United States
Yugang Sheng
Affiliation:
yugang.sheng@gmail.com, The University of Iowa, Physics and Astronomy, 188 IATL, Iowa city, IA, 52242, United States
Markus Wohlgenannt
Affiliation:
markus-wohlgenannt@uiowa.edu, The University of Iowa, Physics and Astronomy, 188 IATL, Iowa city, IA, 52242, United States
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Abstract

We experimentally test three existing models of organic magnetoresistance (OMAR) which are all based on carrier spin dynamics. We first prove that hyperfine field originating from the hydrogen nuclei in organic materials is necessary for observing OMAR by studying C60 sandwich devices using several different electrode materials. We show that C60, unlike many other organic semiconductors, does not exhibit any intrinsic OMAR effect. However, we find that as soon as the carriers in C60 are brought in proximity with hydrogen-containing compounds, either in the form of a polymeric electrode, or side-chain substituents, a weak OMAR effect is observed. Next, we perform charge-induced absorption and electroluminescence spectroscopy in a polyfluorene organic magnetoresistive device. Our experiments allow us to measure the singlet exciton, triplet exciton and polaron densities in a live device under an applied magnetic field, and to distinguish between three models of OMAR. These models are based on different spin-dependent interactions, namely exciton formation, triplet exciton-polaron quenching and bipolaron formation. We show that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. Our data are inconsistent with the exciton formation and triplet-exciton polaron quenching models.

Keywords

magnetoresistance (transport)organicthin film
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1032: Symposium I – Nanoscale Magnetic Materials and Applications , 2007 , 1032-I10-20
Copyright
Copyright © Materials Research Society 2008

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