New magnet type promises enhanced data storage

Technology News | February 14, 2019

By Rich Pell

Compared to conventional magnets in which small magnetic constituents align with one another to create a strong magnetic field, the new “singlet-based” magnet has fields that pop in and out of existence and stick to one another in aligned clumps. While this results in an unstable force, say the researchers, it is also one that potentially has more flexibility than its conventional counterparts.

“There’s a great deal of research these days into the use of magnets and magnetism to improve data storage technologies,” says Andrew Wray, an assistant professor of physics at New York University, who led the research team. “Singlet-based magnets should have a more sudden transition between magnetic and non-magnetic phases. You don’t need to do as much to get the material to flip between non-magnetic and strongly magnetic states, which could be beneficial for power consumption and switching speed inside a computer.”

In addition, say the researchers, there’s also a big difference in how this kind of magnetism couples with electric currents.

“Electrons coming into the material interact very strongly with the unstable magnetic moments, rather than simply passing through,” says Wray. “Therefore, it’s possible that these characteristics can help with performance bottlenecks and allow better control of magnetically stored information.”

The idea for this type of magnet is not new and dates back to the 1960s. While conventional magnets contain a host of tiny “magnetic moments” that are locked into alignment with other magnetic moments to create a magnetic field, early researchers theorized that a material that lacks magnetic moments might still be able to be a magnet.

The idea works because of a kind of temporary magnetic moment called a “spin exciton,” say the researchers, which can appear when electrons collide with one another under the right conditions.

“A single spin exciton tends to disappear in short order,” says Wray, “but when you have a lot of them, the theory suggested that they can stabilize each other and catalyze the appearance of even more spin excitons, in a kind of cascade.”

In this latest study, the researchers sought to uncover this phenomenon. Several candidates had been found dating back to the 1970s, but all were difficult to study, with magnetism only stable at extremely low temperatures.

The latest candidate – USb₂, a compound of uranium and antimony – was found using neutron scattering, X-ray scattering, and theoretical simulations, enabling the researchers to establish a link between the behaviors of this far more robust magnet and the theorized characteristics of singlet-based magnets.

“This material had been quite an enigma for the last couple of decades – the ways that magnetism and electricity talk to one another inside it were known to be bizarre and only begin to make sense with this new classification,” says Lin Miao, an NYU postdoctoral fellow and the first author of a paper on the research.

Specifically, say the researchers, they found that USb2 holds the critical ingredients for this type of magnetism – particularly a quantum mechanical property called “Hundness” that governs how electrons generate magnetic moments. Hundness has recently been shown to be a crucial factor for a range of quantum mechanical properties, including superconductivity.

For more, see “High temperature singlet-based magnetism from Hund’s rule correlations.”