Magnetic imaging and statistical analysis of the metamagnetic phase transition of FeRh with electron spins in diamond

TL;DR

This study uses NV-center magnetic imaging combined with statistical analysis to investigate the temperature-driven metamagnetic phase transition in FeRh, revealing domain dynamics, transition temperature, hysteresis, and domain wall reorientation.

Contribution

It introduces a statistical analysis method for NV magnetic imaging data to characterize phase transitions and domain behavior in magnetic materials.

Findings

Identified nucleation, growth, and coalescence regimes of ferromagnetic domains.

Extracted transition temperature and hysteresis width from magnetic-field maps.

Detected domain wall reorientation across the phase transition.

Abstract

Magnetic imaging based on nitrogen-vacancy (NV) centers in diamond has emerged as a powerful tool for probing magnetic phenomena in fields ranging from biology to physics. A key strength of NV sensing is its local-probe nature, enabling high-resolution spatial images of magnetic stray fields emanating from a sample. However, this local character can also form a drawback for analysing the global properties of a system, such as a phase transition temperature. Here, we address this challenge by using statistical analyses of magnetic-field maps to characterize the first-order temperature-driven metamagnetic phase transition from the antiferromagnetic to the ferromagnetic state in FeRh. After imaging the phase transition and identifying the regimes of nucleation, growth, and coalescence of ferromagnetic domains, we statistically characterize the spatial magnetic-field maps to extract the transition temperature and thermal hysteresis width. By analysing the spatial correlations of the maps and their dependence on an external magnetic field, we investigate the magnetocrystalline anisotropy and detect a reorientation of domain walls across the phase transition. The employed statistical approach can be extended to the study of other magnetic phenomena with NV magnetometry or other sensing techniques.