Structural origin of inhomogeneous properties in (fluoranthene)2PF6 crystals

Comparison of 2-D ESR imaging techniques in two frequency ranges

“…3). In the original analysis, a color code was used to code the spin density maps [14,19]. It resolves small changes in the spin density in a much better way than does a grey code and allowed us to discern inner features of the samples that are lost in Fig.…”

“…Due to individual growth conditions, or manipulated by radiation damage, (FA)2PF 6 samples may contain between 10 -5 and 10 -2 Curie-like paramagnetic defects per formula unit [12,13]. Even in single crystals of (FA)2PF6, growth sectors with varying defect concentration and thus varying physical properties may be found [14]. These represent interesting subjects for ESR imaging.…”

Three-dimensional cylindrical X-band ESR imaging by a combined pulsed gradient Fourier and static gradient projection reconstruction method

“…We selected hollow crystals with shiny black surfaces, preventing thus problems related with the skin depth (microwave conductivity r i % 50 S cm À1 , anisotropy r i : r^> 100:1). Due to varying defect concentration in the range of about 1 Curie-like defect per 1000 formula units, the conduction electron spin relaxation times T 1 and T 2 (of about 8 ls) and the diffusion coefficient (D i % 1 cm 2 /s) are spatially non-homogeneous in these samples [4], whereas orientation of the crystal axes is uniform [3]. Thus they present valuable model systems for imaging attempts.…”

“…Thus they present valuable model systems for imaging attempts. (FA) 2 PF 6 crystals have a Peierls-like metal-non-metal transition at T p = 186 K [3,18]. The conduction electron spin resonance measurements presented below were therefore performed at T = 250 K > T p , close to the crystal growth temperature, and thus sufficiently below room temperature for improved sample stability.…”

“…However, their single crystals tend to exhibit growth sectors [3], or even holes in the center [4], and defects-statistically distributed or arbitrarily introduced by irradiation-can modify their physical properties drastically and spatially non-uniformly [4][5][6]. Thus an easy to apply ESR imaging technique, copying the advantages of NMR microscopy [7], is of particular interest.…”