Characterization of ferrimagnetic materials using diamond Nitrogen-Vacancy centers
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2025
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Abstract
Nitrogen–vacancy (NV) centers in diamond have emerged as versatile quantum sensors capable of probing nanoscale magnetic noise with high spatial and spectral resolution. Within this framework, NV center relaxometry has been successfully employed to study ferromagnetic and antiferromagnetic systems. However, ferrimagnetic materials remain largely unexplored, despite their tunable properties arising from temperature-cdependent compensation points that allow them to emulate either ferromagnetic or antiferromagnetic behavior. In this work, we develop a theoretical framework for incorporating ferrimagnets into the NV relaxometry picture. We construct a model system for a prototypical GdFeCo alloy, represented by two interpenetrating face-centered-cubic sublattices, and recover the temperature dependence of the magnon frequencies by scaling the effective fields with the macroscopic magnetization of each sublattice. The calculated NV center relaxatioxn rates exhibit antiferromagnetic-like features in the vicinity of the angular momentum compensation temperature and show an overall monotonic increase with temperature. This behavior results from the combined effects of reduced magnon frequencies due to field scaling and the enhanced thermal magnon populations governed by Bose–Einstein statistics and effective damping. The relaxation rates exhibit antiferromagnetic-like behavior in the vicinity of the angular momentum compensation temperature, comparable to those reported for NiO and MnF2. Far from this point, they recover ferromagnetic-like characteristics similar to those observed in materials such as YIG. Deviations from this behavior arise near the magnetization compensation temperature and close to the Curie temperature, where numerical instabilities limit the reliability of the calculations.
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Tesis (Master’s degree in Physics)--Pontificia Universidad Católica de Chile, 2025