Longitudinal and transverse diffusion of conduction-electron spins on stacks of fluoranthene radical cations

Abstract

The temperature dependence and anisotropy of the conduction-electron spin diffusion coefficient D͑T͒ of three single crystals of the organic conductor ͑fluoranthene͒ 2 PF 6 with defect content varying between 7 ϫ 10 −5 and 1% per formula unit have been determined. D ʈ / D Ќ varies between 2 ϫ 10 4 and 100 in the metallic phase. The defect dependences of the Peierls transition, microwave conductivity, magnetic susceptibility, and transverse relaxation rate are presented as well and their relations are discussed.

ESR Imaging of Conduction Electrons in Organic Conductors

“… T 1 map derived from a slice in a (FA) 2 PF 6 single crystal. Pixel volume ( X × Y × Z ) is (100 × 30 × 45) m̈m 3 . The graphs represent detailed T 1 values fitted for the indicated regions of the image 21 …”

“…It is thus concluded that the systematic variation of the defect content in the different growth sectors is of relevance in spite of its low absolute value (10—1000 ppm per formula unit range). The diffusion coefficient parallel to the stacking axis is reduced for increasing defect content, whereas the perpendicular component increases, but to a much smaller extent 3 . In most simple non‐magnetic metals, defect spins relax faster to the lattice than conduction electron spins, thus their mutual exchange interaction is in favor of the total conduction electron spin‐lattice relaxation.…”

“…For 3D or electric current imaging, pulsed G y and G z gradients were realized with two sets of coils inside the dielectric ring resonator, whereas a switchable G x gradient was available via a quadrupolar coil system on the outside of the metal cryostat 12b,17,18 . Figure 3 shows as an example a low‐resolution (30 × 200 × 30 m̈m 3 ) spin density image of the same (FA) 2 PF 6 crystal that is photographed in Fig. 1.…”

“… Low‐resolution spin density images of the (FA) 2 PF 6 crystal shown in Fig. 1 recorded by 3D cylindrical imaging at X‐band with one static G z,x gradient and one pulsed G y gradient, together with a 1‐mm grid (5° steps/32 k y ‐lines, 30 × 200 × 30 m̈m 3 volume elements. ) 13 …”

“…Most generally, however, diffusion is restricted with a characteristic length of the chain length distribution of about 100 m̈m 10 . The anisotropy of the diffusion coefficient can be reduced from above 10 4 :1 to below 100:1 for increasing defect content 3,10a,b . Restrictions to free diffusion can be introduced arbitrarily, e.g., by geometrically structured radiation damage 11 .…”