In conventional magnets, small magnetic constituents align with one another to create a strong magnetic field. By contrast, the newly-discovered type of magnet — the singlet-based magnet — has fields that pop in and out of existence, resulting in an unstable force.
In a normal magnetic material, dense magnetic moments try to align with their neighbors (left); by contrast, in a singlet-based material, unstable magnetic moments pop in and out of existence, and stick to one another in aligned clumps (right). Image credit: Lin Miao, New York University.
The idea for singlet-based magnets dates back to the 1960s, based on a theory that stood in sharp contrast to what had long been known about conventional magnets.
A typical magnet contains a host of tiny ‘magnetic moments’ that are locked into alignment with other magnetic moments, all acting in unison to create a magnetic field. Exposing this assembly to heat will eliminate the magnetism; these little moments will remain — but they’ll be pointing in random directions, no longer aligned.
A pioneering thought five decades ago, by contrast, posited that a material that lacks magnetic moments might still be able to be a magnet. This sounds impossible, but it works because of a kind of temporary magnetic moment called a ‘spin exciton,’ which can appear when electrons collide with one another under the right conditions.
“A single spin exciton tends to disappear in short order, 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,” said lead author Dr. Andrew Wray, a researcher at New York University.
In the new study, Dr. Wray and colleagues 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.
Using neutron scattering, X-ray scattering, and theoretical simulations, the physicists established a link between the behaviors of a far more robust magnet, the uranium antimonide USb2, 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,” said first author Dr. Lin Miao, a postdoctoral researcher at New York University.
Specifically, the team 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.
“There’s a great deal of research these days into the use of magnets and magnetism to improve data storage technologies,” Dr. Wray said.
“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.”
The findings were published in the journal Nature Communications.
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Lin Miao et al. 2019. High temperature singlet-based magnetism from Hund’s rule correlations. Nature Communications 10, article number: 644; doi: 10.1038/s41467-019-08497-3
