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Diamonds have the reputation as flawless, sparkling gems. In scientific applications, their hardness is used to test the highest pressure levels. But researchers at the Ames Laboratory plan to exploit defects in diamond’s crystal structure, known as nitrogen vacancy centers, to build a device that will give them the ability to visualize magnetic fields produced by magnetic nanostructures.

While the technology is relatively new, the physics behind the phenomena is fairly well-established. In fact, some major contributions in this area have come from Ames Lab theorist, Viatcheslav Dobrovitski and his colleagues.

“The nitrogen-vacancy centers in diamond are quite unique, combining long quantum spin lifetimes with unusual coupling between spin state and the optical properties of the center,” Dobrovitski says. “This opens the way to using them as very sensitive and efficient detectors of classical magnetic field and surrounding quantum spins, as well as detectors for electric field, temperature, etc. Nowadays, many groups are pursuing the possible application of the NV centers for nanoscale magnetometry.”

According to Dobrovitski, researchers at several institutions, such as Harvard, Berkeley, and Delft, have this technology, but are taking different approaches. Ames Lab’s Ruslan Prozorov, an experimentalist and leader of Ames Lab’s nanoscale efforts, plans to create another group here by building a magnetic nanoscope to study magnetic materials at the nanoscale.

“The fundamental physics is the same, but there’s no single recipe for how to do it,” Prozorov says. “So it comes down to an actual task at hand and the scientific goals. Most groups are interested in pushing the technology to the limit for the sake of engineering progress.”

"Our goal is different – we need a versatile instrument to study various magnetic nano- and meso-structures produced at the Ames Lab and by our collaborators elsewhere,” Prozorov explains. “In particular, we plan to study magnetic ‘nanoislands’ that fellow Ames Lab physicist Michael Tringides has grown on graphene as well as bio-inspired magnetic nanoparticles similar to those grown in vivo by magnetotatic bacteria that are being studied and grown in vitro by Ames Lab scientist Surya Mallapragada’s research group.”

“In simple terms, if you shine a laser light on a NV-center defect, it will induce photoluminescence whose intensity depends on the magnetic field at the location of the defect,” says Prozorov. “The defects are very small – just a few angstroms across and are extremely sensitive to the magnitude of the magnetic field. It is possible to detect signals at the levels of a single electron.”

While other techniques have yielded many important results, the sensitivity of the new equipment would provide a much better look at what’s taking place. Dobrovitski’s theoretical expertise will prove very useful in designing Ames Lab’s new equipment.

“During the last few years, I have been working on controlling the dynamics of the NV centers, and harnessing them for quantum spin detection,” Dobrovitski says. “Some of my previous results, and the work planned in the future, will be useful for designing different modes of operation of the NV microscope. When the microscope is built, this theoretical work will provide guidance for Ruslan, and supply him with the tools for the planned future work.”

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Measuring the magnetic field of
nanoparticles produced by magneto-
tatic bacteria (left) and dysprosium
nanoislands (right) are just two
potential uses for new equipment
that Ames Lab physicist Ruslan
Prozorov plans to build.

Ultimately, Prozorov hopes to develop a dedicated nano- and meso-scale magnetic imaging research facility that combines existing capabilities, such as magneto-optics and magnetic-force microscopy with this new state-of-the-art nitrogen-vacancy magnetoscope and other techniques, such as magnetic-force resonant imaging.

“Ultimately, we want to be able to probe very small magnetic fields at the length scales from nanometers to millimeters,” Prozorov says. “It won’t happen overnight, but our goal is to have first data to show by the next DOE (program) review.”

“The critical element will be to find good postdocs to carry out the work,” Prozorov concludes. “Currently, we’re looking for one experimentalist and one theorist to make it happen and Ames Lab has already allocated space and resources to build the device.”

~ by Kerry Gibson

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Ames Lab physicists Ruslan Prozorov (left) and Viatcheslav Dobrovitski are involved in developing new, sensitive instrumentation that will allow the visualization of magnetic fields produced by nano-scale particles. Dobrovitski has been involved in the theoretical work behind nitrogen-vacancy centers, a defect in the crystal structure of diamond that Prozorov hopes to be able to use to measure minute magnetic fields of nanomaterials.