A dense layer of nitrogen-vacancy (NV) centers near the surface of a diamond can be interrogated in a widefield optical microscope to produce spatially resolved maps of local quantities such as magnetic field, electric field, and lattice strain, providing potentially valuable information about a sample or device placed in proximity. Since the first experimental realization of such a widefield NV microscope in 2010, the technology has seen rapid development and demonstration of applications in various areas across condensed matter physics, geoscience, and biology. This Perspective analyzes the strengths and shortcomings of widefield NV microscopy in order to identify the most promising applications and guide future development. We begin with a brief review of quantum sensing with ensembles of NV centers and the experimental implementation of widefield NV microscopy. We then compare this technology to alternative microscopy techniques commonly employed to probe magnetic materials and charge flow distributions. Current limitations in spatial resolution, measurement accuracy, magnetic sensitivity, operating conditions, and ease of use are discussed. Finally, we identify the technological advances that solve the aforementioned limitations and argue that their implementation would result in a practical, accessible, high-throughput widefield NV microscope.
Interest in van der Waals materials often stems from
a desire to
miniaturize existing technologies by exploiting their intrinsic layered
structures to create near-atomically thin components that do not suffer
from surface defects. One appealing property is an easily switchable
yet robust magnetic order, which is only sparsely demonstrated in
the case of in-plane anisotropy. In this work, we use widefield nitrogen-vacancy
(NV) center magnetic imaging to measure the properties of individual
flakes of CuCrP2S6, a multiferroic van der Waals
magnet known to exhibit weak easy-plane anisotropy in the bulk. We
chart the crossover between the in-plane ferromagnetism in thin flakes
down to the trilayer and the bulk behavior dominated by a low-field
spin-flop transition. Further, by exploiting the directional dependence
of NV center magnetometry, we are able to observe an instance of a
predominantly out-of-plane ferromagetic phase near zero field, in
contrast with our expectation and previous experiments on the bulk
material. We attribute this to the presence of surface anisotropies
caused by the sample preparation process or exposure to the ambient
environment, which is expected to have more general implications for
a broader class of weakly anisotropic van der Waals magnets.
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