ITHACA, NY – Coming to a lab near you: A magneto-thermal imaging method that delivers nanoscale and picosecond resolution previously only available at synchrotron facilities.

This innovation in spatial and temporal resolution will provide researchers with extraordinary insights into the magnetic properties of a range of materials, from metals to insulators, all in the comfort of their laboratories, potentially stimulating the development of magnetic storage devices. .

“Magnetic X-ray microscopy is a relatively rare bird,” said Greg Fuchs, associate professor of applied physics and engineering, who led the project. “Magnetic microscopies that can do this kind of spatial and temporal resolution are very rare. Normally you have to choose either space or time. You can’t get them both. There are only four or five. places in the world … that have that capability. So having the ability to do that on a table really allows for nanoscale spin dynamics for research. “

His team paper, “Nanoscale Magnetization and Current Imaging Using Time-Resolved Scanning-Probe Magnetothermal Microscopy,” published June 8 in the Journal of the American Chemical Society Nano letters. Principal author is postdoctoral researcher Chi Zhang.

The article is the culmination of a nearly 10-year effort by the Fuchs Group to explore magnetic imaging with magneto-thermal microscopy. Instead of detonating a material with light, electrons, or x-rays, researchers use a laser focused on the scanning probe to apply heat to a microscopic strip of a sample and measure the resulting electrical voltage to get local magnetic information.

Fuchs and his team pioneered this approach and over the years have developed an understanding of how temperature gradients change in time and space.

“You think of the heat as being a very slow diffusion process,” Fuchs said. “But actually, scattering at nanoscale lengths has picosecond times. And that’s a key insight. It’s what gives us the temporal resolution. Light is a wave and diffracts. It doesn’t want to. not live at these very small scales of length. But the heat can. “

The group has already used this technique to image and manipulate antiferromagnetic materials, which are difficult to study because they do not produce a magnetic field, as well as magnetic metals and insulators.

While it is quite easy to focus a laser, the main obstacle has been to confine that light and generate enough heat at the nanoscale for the process to work. And because some phenomena on this scale happen so quickly, the imaging must be just as fast.

“There are a lot of situations in magnetism where things move, and it’s small. And that’s basically what you need,” Fuchs said.

Now that they have refined the process and successfully achieved a spatial resolution of 100 nanometers and a temporal resolution of less than 100 picoseconds, the team can explore the true minutiae of magnetism, such as skyrmions, which are quasi-particles in which the magnetic order is twisted. Understanding these types of “spin textures” could lead to new high-speed, high-density logic and magnetic storage technologies.

In addition to magnetism, the technique’s dependence on electrical voltage means that it can be used to measure current density when voltage interacts with a material. This is a new approach because other imaging techniques measure current by measuring the magnetic field produced by the current, not the current itself.

Magneto-thermal microscopy has its limits. Since samples must be configured with electrical contacts, the material must be modeled in an apparatus. As a result, the technique cannot be applied to bulk samples. In addition, the device and the scanning probe must be scaled together. So if you want to measure nanoscale phenomenon, the sample should be small.

But these limitations are minor compared to the benefits of a relatively inexpensive form of magneto-thermal microscopy in your own laboratory.

“Right now, people have to go to a public facility, like a synchrotron facility, to do these kinds of measurements,” Zhang said. “You write a proposal, you get a bundle time and you maybe have a few weeks to work, at best. If you don’t get the result you want, then it might be a few more months. therefore progress for the field. “

– This press release was originally published on the Cornell University website



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