Physicists at the University of Iowa have proposed a new technique for detecting and measuring materials that give off weak magnetic signals or have no magnetic field at all. Their solution uses a non-invasive diamond probe to induce a magnetic response in the material being studied and then detect how that response changes the probe's own magnetic field.
This technique has many potential real-world applications, including yielding more sensitive magnetic resonance imaging (MRI) machines, developing high-speed-storage memory in the semiconducting industry, and producing more efficient computer processing units (CPUs).
"This approach is designed to measure the situation where if you didn't have the probe nearby, you'd see nothing. There wouldn't be any magnetic fields at all," says Michael Flatté, physics and astronomy professor and senior author of a paper on this work in Physical Review Letters. "It's only the probe itself that's causing the presence of the magnetic fields."
The probe does this by creating ‘magnetic moments’ in materials that otherwise would emit a weak magnetic field or have no magnetic field at all. Magnetic moments occur when a group of electrons orient themselves in the same direction, much like tiny compass needles all pointing, say, north. That uniform orientation creates a tiny magnetic field. Iron, for example, produces a strong response because most of its electrons become oriented in the same direction when it encounters a magnetic force.
All it takes for the diamond probe, which is just a few nanometers in diameter, to create a magnetic moment is for two of its six electrons to snap to the same directional orientation. When that happens, the probe stimulates electrons in materials with weak or non-existent magnetic fields to re-orient themselves, creating a magnetic moment in the material that is strong enough to be detected by the probe. How the material's magnetic moment influences the probe's own magnetic field is measurable, providing researchers with the means to calculate the material's physical dimensions, such as its thickness.
"These electrons (in materials with weak or non-existent magnetic fields) have their own field that acts back on the probe and distorts the probe [in a way] that you can then measure," says Flatté, director of the University of Iowa 's Optical Science Technology Center.
This becomes important when trying to capture the dimensions of magnetic layers that are buried or sandwiched between non-magnetic layers. Such situations arise when working with semiconductors and will become more commonplace as computer processing advances. "We calculate the magnetic response, and from that we would know where the magnetic fields end and thus know the layer thickness," Flatté explains.
This concept builds upon an emerging sampling approach called nitrogen-vacancy center magnetometry, in which a defect is introduced into a diamond's crystal structure (by replacing two carbon atoms with a nitrogen atom). It is effective in part because the probe it uses is made of diamond, which creates small magnetic moments that are key to detecting magnetic fields in the studied materials.
But there is a drawback: nitrogen-vacancy center magnetometry only works with magnetized materials. That rules out using it to study superconductors, where the magnetic field ceases to exist at certain temperatures, and many other materials. Flatté and co-author Joost van Bree's proposed solution gets around this limitation by using the probe to create a magnetic field that forces materials with weak or non-existent magnetic fields to react to it.
"If you apply a magnetic field to a superconductor, it will attempt to cancel that magnetic field applied to it," Flatté says. "Even though it's doing that, it creates a magnetic field outside of itself that then affects the spin centers. That's what then can be detected."
This story is adapted from material from the University of Iowa, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.