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Evidence of a Long-Predicted Magnet

Half a century ago, theorists proposed a novel way for materials to produce a magnetic field. The prediction diverged from the way small magnetic constituents slowly align in conventional materials to create a strong magnetic field. Now, scientists have discovered a uranium compound that bears out that long-ago theory—a new type of magnet that holds promise for enhancing the performance of data storage technologies.

The singlet-based magnet has magnetic constituents that pop in and out of existence, making it easier to swing into—or out of—a strongly magnetic state. The key ingredient for this is a “spin exciton,” a temporary magnetic constituent that can appear spontaneously when electrons and atoms jostle around inside the material. When enough spin excitons come together, they can stabilize each other and catalyze the appearance of even more spin excitons in a cascade that leads to magnetism.

At Advanced Light Source (ALS) Beamline 4.0.3, x-ray absorption spectroscopy measurements on the uranium compound USb2 showed that the electrons in uranium behave in a way that matches this scenario. The unconventional, singlet-based electronic environment provides natural explanations for a number of enigmatic properties of the material, including anomalies previously seen in the resistivity and heat capacity within the magnetic phase.

Whereas earlier candidates for singlet-based magnets had transition temperatures around -270°C, the magnetic phase in USb2 occurs at temperatures around -70°C and can be sustained up to higher temperatures under pressure. With some chemical tuning, a magnetic phase at room temperature could be within reach—along with new data storage solutions.

In a normal magnetic material, dense magnetic constituents try to align with their neighbors (left). By contrast, in a singlet-based material, unstable magnetic constituents pop in and out of existence, and stick to one another in aligned clumps (right). (Credit: Lin Miao/New York University Department of Physics)

L. Miao, R. Basak, S. Ran, Y. Xu, E. Kotta, H. He, J.D. Denlinger, Y.-D. Chuang, Y. Zhao, X. Xu, J.W. Lynn, J.R. Jeffries, S.R. Saha, I. Giannakis, P. Aynajian, C.-J. Kang, Y. Wang, G. Kotliar, N.P. Butch, and L.A. Wray, “High temperature singlet-based magnetism from Hund’s rule correlations,” Nat. Commun. 10, 644 (2019), doi:10.1038/s41467-019-08497-3.

Adapted from the NYU news release, “Scientists Discover New Type of Magnet.”