Experimental Tests of Possible Mechanisms for the Organic Magnetoresistive Effect

2007 ◽  
Vol 1032 ◽  
Author(s):  
Tho Duc Nguyen ◽  
James Rybicki ◽  
Yugang Sheng ◽  
Markus Wohlgenannt
Keyword(s):  
Magnetic Field ◽  
Organic Semiconductors ◽  
Electrode Materials ◽  
Spin Dynamics ◽  
Experimental Tests ◽  
Triplet Exciton ◽  
Side Chain ◽  
Singlet Exciton ◽  
Organic Magnetoresistance ◽  
Magnetoresistive Effect

AbstractWe 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.

scholarly journals Ядерная спиновая динамика и флуктуации в анизотропной модели большого ящика

2022 ◽  
Vol 64 (2) ◽  
pp. 206
Author(s):  
А.В. Шумилин ◽  
Д.С. Смирнов
Keyword(s):  
Magnetic Field ◽  
Organic Semiconductors ◽  
Nuclear Spin ◽  
Spin Dynamics ◽  
Spin Model ◽  
Zero Magnetic Field ◽  
Current Fluctuations ◽  
Nuclear Spins ◽  
Spin Noise ◽  
Analytical Expressions

We consider the central spin model in the box approximation taking into account an external magnetic field and the anisotropy of the hyperfine interaction. From the exact Hamiltonian diagonalization we obtain analytical expressions for the nuclear spin dynamics in the limit of many nuclear spins. We predict the nuclear spin precession in zero magnetic field for the case of the anisotropic interaction between electron and nuclear spins. We calculate and describe the nuclear spin noise spectra in the thermodynamic equilibrium. The obtained results can be used for the analysis of the nuclear spin induced current fluctuations in organic semiconductors.

Large Magnetoresistance at Room Temperature in Organic Semiconductor Sandwich Devices

2005 ◽  
Vol 871 ◽  
Author(s):  
Govindarajan Veeraraghavan ◽  
Omer Mermer ◽  
Thomas Lee Francis ◽  
Yugang Sheng ◽  
Tho Duc Nguyen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Film Thickness ◽  
Organic Semiconductors ◽  
Applied Magnetic Field ◽  
Room Temperature ◽  
Electrode Materials ◽  
Bulk Material ◽  
Temperature Dependent ◽  
Semiconducting Polymer ◽  
Mr Effect

AbstractWe describe a recently discovered magnetoresistance (MR) effect in semiconducting polymer and small molecule sandwich devices. The MR effect reaches up to 10% in a magnetic field of 10mT at room temperature. This MR effect is therefore amongst the largest of any bulk material. We characterize this effect and discuss its dependence on voltage, film thickness, temperature, electrode materials and (unintentional) impurity concentration in three different organic semiconductors. We found that the MR effect is only weakly temperature dependent and does not depend on sign and direction of the applied magnetic field. To the best of our knowledge, the discovered MR effect is not adequately described by any of the mechanisms known to date.

The rise of organic magnetoresistance: materials and challenges

2017 ◽  
Vol 5 (23) ◽  
pp. 5572-5580 ◽  
Author(s):  
Marco Gobbi ◽  
Emanuele Orgiu
Keyword(s):  
Organic Semiconductors ◽  
Recent Progress ◽  
Organic Magnetoresistance ◽  
Magnetoresistive Effect

This paper provides a brief review of recent progress regarding the magnetoresistive effect observed in organic semiconductors.

Role of Perfluorophenyl Group in the Side Chain of Small-Molecule n-Type Organic Semiconductors in Stress Stability of Single-Crystal Transistors

2021 ◽  
pp. 2095-2101
Author(s):  
Shohei Kumagai ◽  
Craig P. Yu ◽  
Shunsuke Nakano ◽  
Tatsuro Annaka ◽  
Masato Mitani ◽  
...  
Keyword(s):  
Single Crystal ◽  
Organic Semiconductors ◽  
Small Molecule ◽  
Side Chain

MAGNETOSTATIC MODES IN NANOMETER-SIZED FERROMAGNETIC AND ANTIFERROMAGNETIC TUBES

2007 ◽  
Vol 14 (03) ◽  
pp. 471-480 ◽  
Author(s):  
T. K. DAS ◽  
M. G. COTTAM
Keyword(s):  
Magnetic Field ◽  
Spin Dynamics ◽  
Continuum Theory ◽  
Inelastic Light Scattering ◽  
Dipole Interactions ◽  
Large Length ◽  
Magnetostatic Modes ◽  
Magnetostatic Spin Waves ◽  
Macroscopic Continuum ◽  
Cylindrical Axis

A theory is presented for the magnetostatic modes in ferromagnetic and antiferromagnetic nanotubes, which have a large length-to-radius aspect ratio and an external magnetic field parallel to the cylindrical axis. The surface and bulk magnetic excitations (or magnetostatic spin waves) are studied for cases where the dipole–dipole interactions are dominant in the spin dynamics. This situation can be realized at sufficiently small wavevectors by inelastic light scattering or magnetic resonance techniques. A macroscopic continuum theory is developed, using the magnetostatic form of Maxwell's equations and the electromagnetic boundary conditions, and the characteristic equations (or dispersion relations) are deduced for the magnetostatic modes. Numerical calculations are presented for ferromagnetic and antiferromagnetic nanostructures, taking Ni 80 Fe 20 and MnF 2, respectively. The spatial variations of the mode amplitudes are also investigated.

Magnetic ground state of low-doped manganites probed by spin dynamics under magnetic field

2004 ◽  
Vol 272-276 ◽  
pp. 1784-1786 ◽  
Author(s):  
P. Kober ◽  
M. Hennion ◽  
F. Moussa ◽  
A. Ivanov ◽  
L.-P. Regnault ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Ground State ◽  
Spin Dynamics ◽  
Magnetic Ground State ◽  
Doped Manganites

scholarly journals Spin transport and spin dynamics in antiferromagnets

2021 ◽  
Author(s):  
◽  
Geert Hoogeboom
Keyword(s):  
Magnetic Field ◽  
Heavy Metal ◽  
Spin Transport ◽  
Spin Dynamics ◽  
Magnetic Moments ◽  
Spin Current ◽  
Active Role ◽  
Metal Films ◽  
Alternating Direction ◽  
High Processing

Ferromagnets (FMs) have been a key ingredient in information technology because it is easy to manipulate and read out the magnetization. Antiferromagnets (AFMs) have magnetic moments with alternating direction resulting in negligible magnetization. This gives them high processing and device downscaling features, but this also makes it challenging to manipulate and interact with the AFM order. This thesis studies this interaction with antiferromagnets. NiO AFM order has been read out by electrically injecting spin current via the spin Hall effect in thin heavy metal films. In DyFeO3, both Dy and Fe magnetic moments, their excitation and interaction have been probed. A magnetic field lifts the degeneracy of magnetic excitations with opposite magnon spin, allowing a spin current to be detected nonlocally. The AFM order and the generation of spin current can easily be controlled by an adjacent FM. Thereby, we show that AFMs have the potential to play an active role in spintronics.

scholarly journals Tribological Evolution of the Superficial Layer and the Effects of the Magnetic Field to a Non- conventional Treated Steel, During Wear Tests

2018 ◽  
Vol 55 (3) ◽  
pp. 442-446
Author(s):  
Carmen Penelopi Papadatu ◽  
Andrei Victor Sandu ◽  
Marian Bordei ◽  
Ioan Gabriel Sandu ◽  
Sorin Ciortan
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Dry Friction ◽  
Experimental Tests ◽  
Superficial Layer ◽  
Alloyed Steel ◽  
Wear Process ◽  
The Magnetic Field ◽  
Wear Tests ◽  
Made In

The article focuses on the behavior of the non-conventional treated alloyed steel in magnetic field, during the dry wear tests. It is a review of the experimental tests from last years. The thermo-magnetic treatments have been applied before the application of a thermo-chemical treatment in plasma based on diffusion process. The study was made in order to improve the mechanical properties of the alloyed steel during the friction wear. Thermo-magnetic treatment applied before the plasma nitro-carburizing treatment improves the mechanical properties of the material especially in this case, for a steel that has a considerable content of Chromium (1.02%). The behavior was studied using X-Ray diffractometry of the superficial layers during the dry friction of wear process. The wear tests used an Amsler machine, during three hours of wear tests. After each hour of the wear tests the samples have been analyzed. The diffractometric characteristics of the superficial layers obtained after a complex array of thermo-magnetic and thermo-chemical in plasma treatments, the phases distribution, the content of the superficial layers and the behavior of the steel during the wear through dry friction tests, have been considered as criteria.

scholarly journals Exploration of the close chemical space of tryptophan and tyrosine reveals importance of hydrophobicity in CW-photo-CIDNP performances

2021 ◽  
Vol 2 (1) ◽  
pp. 321-329
Author(s):  
Felix Torres ◽  
Alois Renn ◽  
Roland Riek
Keyword(s):  
Magnetic Field ◽  
Nuclear Polarization ◽  
Continuous Wave ◽  
Radical Pair ◽  
Chemical Space ◽  
Spin Dynamics ◽  
Basic Mechanism ◽  
Chemical Library ◽  
Chemically Induced ◽  
Small Chemical

Abstract. Sensitivity being one of the main hurdles of nuclear magnetic resonance (NMR) can be gained by polarization techniques including chemically induced dynamic nuclear polarization (CIDNP). Kaptein demonstrated that the basic mechanism of the CIDNP arises from spin sorting based on coherent electron–electron nuclear spin dynamics during the formation and the recombination of a radical pair in a magnetic field. In photo-CIDNP of interest here the radical pair is between a dye and the molecule to be polarized. Here, we explore continuous-wave (CW) photo-CIDNP (denoted CW-photo-CIDNP) with a set of 10 tryptophan and tyrosine analogues, many of them newly identified to be photo-CIDNP active, and we observe not only signal enhancement of 2 orders of magnitude for 1H at 600 MHz (corresponding to 10 000 times in measurement time) but also reveal that polarization enhancement correlates with the hydrophobicity of the molecules. Furthermore, the small chemical library established indicates the existence of many photo-CIDNP-active molecules.

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