Studies of implanted muons in organic radicals

Abstract

We have performed semi-empirical molecular dynamics calculations of the electronic and molecular structure of muonium incorporated into the organic radicals 3-quinolyl nitronyl nitroxide (3-QNNN), para-pyridyl nitronyl nitroxide (p-PYNN), phenyl nitronyl nitroxide (PNN) and para-nitrophenyl nitronyl nitroxide (p-NPNN). These materials are of interest because they show ferromagnetic order at very low temperatures and can be effectively studied using implanted positive muons. Our calculations give evidence for a wide variety of possible muonium binding sites in the conjugated ring systems of the materials as well as in the nitronyl nitroxide group and suggest the formation of local spin triplet as well as singlet states near the muon, a result which is supported by recent experiments.

Muon-spin-rotation studies of organic magnets

“…In a real material, the ensemble of muons would not, of course, occupy every position in the unit cell, but would select a small subset of points, chosen roughly 'at random' from the p(B) probability distribution. (The choice is, of course, governed by electrostatic considerations (Valladares et al . 1998), but is, in general, uncorrelated with the magnetic-field distribution.)…”