Ferromagnetic contamination of Ultra-Low-Field-NMR sample containers. Quantification of the problem and possible solutions

TL;DR

This paper investigates ferromagnetic contamination in Ultra-Low-Field NMR sample containers, quantifies its impact on measurements, and explores methods to reduce such contamination to improve experimental accuracy.

Contribution

It provides a detailed analysis of ferromagnetic contamination sources and proposes effective strategies for contamination reduction in ULF-NMR experiments.

Findings

Ferromagnetic contaminants produce measurable static fields affecting ULF-NMR.

Surface chemical analyses identify contamination sources.

Proposed cleaning and material selection methods reduce ferromagnetic presence.

Abstract

The presence of a weak remanence in Ultra-Low-Field (ULF) NMR sample containers is investigated on the basis of proton precession. The high-sensitivity magnetometer used for the NMR detection, enables simultaneously the measurement of the static field produced in the sample proximity by ferromagnetic contaminants. The presence of the latter is studied by high resolution chemical analyses of the surface, based on X-ray fluorescence spectroscopy and secondary ions mass spectroscopy. Methodologies to reduce the contamination are explored and characterized. This study is of relevance in any ULF-NMR experiment, as in the ULF regime spurious ferromagnetism becomes easily a dominant cause of artefacts.