Embedded electron spin decoherence as indicator of the matrix material structure

TL;DR

This study demonstrates that embedded electron spin decoherence measurements can serve as a quantitative indicator of the structure and structural changes in matrix materials, combining theoretical modeling and experimental validation.

Contribution

The paper introduces a novel approach linking electron spin decoherence to matrix material structure, validated through experiments on crystalline, polycrystalline, and amorphous malonic acid.

Findings

Decoherence time scale extremums align with proton dipolar couplings in single crystals.

Orientation averaging yields decoherence profiles in polycrystalline samples.

Amorphous polymorph shows reduced decoherence time scale, confirming structure dependence.

Abstract

In this work the problem of characterizing matrix material structure from embedded electron spin decoherence is studied both theoretically and experimentally. Theoretical calculation using nuclear spin bath model and cluster correlation expansion method shows that the positions of decoherence time scale extremums among single crystal orientations of the matrix material coincide with those of the nearest neighbour proton dipolar couplings. This finding is confirmed by single crystal pulsed EPR experiment performed on $\gamma$-irradiated malonic acid (MA). Electron spin decoherence decay profile in polycrystalline matrix material is obtained from the orientation dependence as an average over sampled orientations on a Fibonacci grid. In addition, it is pointed out theoretically that a further removal of crystal ordering in the nuclear spin bath can reduce decoherence time scale from the polycrystalline value. This prediction is verified experimentally by the Hahn echo time decay scale in a new amorphous polymorph of MA, obtained for the first time by mechanical milling. Thus the embedded electron spin decoherence can be viewed as a quantitative indicator for studying structures and/or structure changes of the matrix material.