Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators

Abstract

Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies.We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators we cover almost five octaves in resonance frequency within a single setup. The measurements with a common π-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency. a)

Morphology effects on spin-dependent transport and recombination in polyfluorene thin films

“…Inhomogeneous broadening of a magnetic resonance line of an amorphous material can result from local hyperfine interactions or a distribution in g-factors which can arise from spin-orbit interactions. In order to determine how much of the resonance width is due to hyperfine coupling, arising from the abundance of hydrogen atoms in PFO, and what contribution results from spin-orbit coupling, multiple resonances were measured using coplanar waveguide resonators operating at different frequencies [46]. This approach is chosen because the two contributions to resonance line widths have different magnetic field dependencies: hyperfine broadening occurs independently of the external magnetic field strength, whereas spin-orbit coupling is manifested by a distribution of g-factors and therefore gains more influence on the spectrum for higher static magnetic field strengths.…”

“…[46] for a different polymer material, the multiple resonance spectra obtained through such a procedure can be analyzed by fitting all spectra simultaneously using a global fit with two field-dependent line widths ΔB 1 and ΔB 2 given by ∆ , and highest (lower curve) frequencies recorded. The curves are shifted along the abscissa by the magnitude of the magnetic field on resonance, / , with γ being the gyromagnetic ratio.…”

Quantitative inverse spin Hall effect detection via precise control of the driving-field amplitude

“…By independently and accurately measuring both the ISHE voltage V i and the driving field amplitude B 1 , we can establish ξ i for any given interface. In experiments that involve inhomogeneous distributions of B 1 , e. g. when the MW is delivered by planar waveguide structures [14,15] is fitted with a superposition of a symmetric (ISHE) and antisymmetric (anomalous Hall effect) contribution [3]. For the random distribution shown in the inset of Fig.…”

Angular-Dependent EDMR Linewidth for Spin-Dependent Space-Charge-Limited Conduction in a Polycrystalline Pentacene

“…Separate information about HFI and SOC on a π-conjugated polymer can be obtained from multiple-frequency EDMR (mf-EDMR) measurements (Joshi et al, 2016). However, the limitations of the methodology used in previous work have precluded determination of the orientational distributions of HFI and SOC, and there have not been any reports of the orientational and resonance frequency dependences of HFI and SOC in organic semiconductors.…”

“…Second, they are not suitable for simultaneous ESR/EDMR measurements, the ESR part of which is needed for calibration of the external resonance magnetic field strength. With EDMR, it is difficult to make anisotropy measurements, even using mf-EDMR with a stripline (Baker et al, 2012) or a coplanar waveguide resonator (Joshi et al, 2016), and cylindrical cavity with a short plunger (Seck and Wyder, 1998), partly because the angle between the device element and the applied microwave direction has to be fixed.…”