Robust absolute magnetometry with organic thin-film devices

Abstract

Magnetic field sensors based on organic thin-film materials have attracted considerable interest in recent years as they can be manufactured at very low cost and on flexible substrates. However, the technological relevance of such magnetoresistive sensors is limited owing to their narrow magnetic field ranges (∼30 mT) and the continuous calibration required to compensate temperature fluctuations and material degradation. Conversely, magnetic resonance (MR)-based sensors, which utilize fundamental physical relationships for extremely precise measurements of fields, are usually large and expensive. Here we demonstrate an organic magnetic resonance-based magnetometer, employing spin-dependent electronic transitions in an organic diode, which combines the low-cost thin-film fabrication and integration properties of organic electronics with the precision of a MR-based sensor. We show that the device never requires calibration, operates over large temperature and magnetic field ranges, is robust against materials degradation and allows for absolute sensitivities of <50 nT Hz−1/2.

Vertical organic spin valves in perpendicular magnetic fields

“…Although no Hanle effect as such has been observed in organic semiconductors, the demonstration of spin precession of conduction electrons in OSC by paramagnetic resonance 24 clearly shows that it the underlying physics is the same for organic and inorganic semiconductors.…”

The spin-Dicke effect in OLED magnetoresistance

“…Such fluctuations could arise from spatial variations in spin-spin couplings experienced by a migrating charge, and should be particularly strong if transport is anisotropic, as in molecular wires 29 . The ability to form collective states of radicalpair spins may find application in coherent control of chemical reactions, but also offers an alternative room-temperature route to permutation-symmetry-based concepts for electrically addressable quantum information processing 30 and fast resonance-based magnetometry 4 , because the effect of power broadening is reduced.…”

“…This parameter range is challenging to probe by electron paramagnetic resonance spectroscopy because thermal magnetic polarization is negligible. It is accessed through spin-dependent conductivity that is controlled by electron-hole pairs of singlet and triplet spin-permutation symmetry without the need of thermal spin polarization 4 Macroscopic phase coherence is a hallmark of many exotic states of matter such as superconductivity, ferromagnetism or BoseEinstein condensation. Such coherence may also emerge between two-level systems, where it is mediated by electromagnetic fields, as described by the Dicke effect in collisional narrowing 5 and superradiance 6 .…”

Hanle effect missing in a prototypical organic spintronic device

“…[10][11][12] Although much progress has been made in explaining interfacial properties, [13][14][15][16][17] progress on the understanding of spin transport in the organic medium met greater difficulties.…”