# Comparing low-field cryogenic nuclear relaxation of hyperpolarized diamond and silicon particles

## TL;DR

This paper compares how hyperpolarized diamond and silicon particles behave under different magnetic fields and temperatures, focusing on their nuclear relaxation properties.

## Contribution

The study reveals distinct magnetic field dependencies of nuclear relaxation in hyperpolarized diamond and silicon particles at low temperatures.

## Key findings

- 13C relaxation in diamond is nearly field-independent above 200 mT but becomes proportional to field strength below that.
- Relaxation in hyperpolarized silicon remains field-independent down to a few mT.
- Diamonds require magnetic fields above 200 mT to maintain long relaxation times.

## Abstract

We report on field cycling experiments with hyperpolarized diamond and silicon particles between 10 mT and 3.4 T at temperatures below 10 K. Diamonds with approximately 54 ppm defects, of which around 58% were P1 centers, were hyperpolarized by continuous-wave dynamic nuclear polarization (DNP) at 3.4 T. For fields above 200 mT, the 13C relaxation in diamond was measured to be nearly independent of the magnetic field. At around 200 mT, the field dependence changed and \documentclass[12pt]{minimal}
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\begin{document}$$T_1$$\end{document} was approximately proportional to the field strength. For example, the relaxation time decreased approximately threefold by reducing the main magnetic field from 200 mT to 75 mT. The 13C relaxation was measured to be independent of the DNP polarization time and nuclear hyperpolarization levels. In contrast, the relaxation of hyperpolarized silicon was found to be independent of the field strength down to a few mT, despite a relatively short time for DNP build-up. The results suggest that magnetic fields greater than approximately 200 mT are required for hyperpolarized diamonds with several ppm of (nitrogen) defects to ensure sufficiently long relaxation times.