Magnetoresistance of polymer diodes in presence of oscillating magnetic fields at radio frequency

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Title Magnetoresistance of polymer diodes in presence of oscillating magnetic fields at radio frequency
Publication Type dissertation
School or College College of Science
Department Physics & Astronomy
Author Waters, David P.
Date 2014-12
Description This work focuses on the study of low-magnetic field (<10mT) magnetoresistance effects of organic polymer diodes based on the n-conjugated polymer MEH-PPV in presence of oscillating magnetic fields in the radio frequency range. In these conditions, the combination of static and ac fields can magnetic resonantly influence the electronspin degree of freedom of localized charge-carrier states. As long as bipolar injection conditions influence the net current of the polymer diode, magnetic-resonance changes of the charge carrier spin state can affect spin-dependent charge carrier recombination rates and therefore the material's conductivity. Since the observed spin-dependent recombination currents are governed by the charge carrier pair's spin-permutation symmetry, magnetoresistance measurements under ac drive allow for the electrical detection of magnetic resonance under very low magnetic field conditions where inductive magnetic resonance detection schemes fail due to a lack of spin polarization. In this thesis, this effect was utilized for two effects. Firstly, for the exploration of a magnetic resonance regime where the driving field B 1 approaches the same magnitude as the static magnetic field B0. When Bi approaches B0, a regime where magnetic resonance effects become nonlinear emerges and interesting collective spin-phenomena occur. This includes spin-cooperativity, where the resonantlydriven spin ensemble assumes a macroscopically collective state. Experiments are presented that tested and confirmed previous theoretical predictions. When B}~B0, the emerging spin-cooperativity of recombining polaron pairs in organic semiconductors can be observed through magnetoresistance measurements. The experiments confirmed the theory in all aspects and demonstrated the emergence of the spin-Dicke effect. Secondly, for the exploration of whether magnetic resonantly-controlled spindependent currents can be used for magnetometry of inhomogeneous magnetic fields. This work is a continuation of the previously introduced idea to utilize spin-dependent charge carrier recombination in organic semiconductors for an absolute low-magnetic field magnetometry that is robust against fluctuating environmental conditions. The work focuses on the measurement of magnetic field distributions in gradient magnetic fields. It is shown that organic semiconductor-based magnetic resonance magnetometers can reveal magnetic field distributions. However, this measurement approach can be compromised by inductive resonance artifacts introduced by the large-bandwidth RF stripline resonators needed to operate the magnetometer.
Type Text
Publisher University of Utah
Subject EDMR; ESR; Magnetoresistance; OLED; Organic; Spin
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © David P. Waters 2014
Format application/pdf
Format Medium application/pdf
Format Extent 2,018,492 bytes
Identifier etd3/id/3292
ARK ark:/87278/s6ck1nqf
Setname ir_etd
ID 196857
Reference URL https://collections.lib.utah.edu/ark:/87278/s6ck1nqf
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