Researchers spot spin swapping in an antiferromagnet

Researchers at Johns Hopkins University, University of Texas at Austin, Northeastern University and Argonne National Laboratory have reported a new quantum phenomenon in antiferromagnetic insulators that could open the door to new ways of powering  spintronic devices.

Antiferromagnetic insulators are advantageous in spintronic applications because of their low stray fields and rapid magnetic dynamics. Controlling their magnetization and reading their magnetic state is critical for these applications, but they are challenging.

Gregory Fiete, a physics professor at Northeastern and co-author of the research, said, “The discovery illuminates “how heat flows in a magnetic insulator, [and] how [researchers] can detect that heat flow.”

The novel effects were demonstrated experimentally by combining lanthanum ferrite (LaFeO3) with a layer of platinum or tungsten. This layered coupling generated a new phenomenon that could develop a new power source for these—and other—nascent technologies.

The movement of electrons through a material generates an electric current and heat current—a heat current results when an external electromagnetic field is applied to materials that conduct electricity.

Arun Bansil, a distinguished university professor in the Department of Physics at Northeastern, said, “Heat is just when these electrons are jiggling around faster or slower, so, as a result, they can carry more or less thermal energy. Usually, the spin current flows in the same direction as the heat current. But, in the specific materials used in this study, “it flows perpendicular to the direction of the heat current.”

The team wanted to create a current of magnetism that generates electrical power, by generating a voltage. They did this by combining antiferromagnetic insulating material (here, LaFeO3) with another heavier element, such as platinum or tungsten, which are conductors. The coupling throws the electrons slightly off-kilter.

Fiete says, “This particular material has the spins that are nearly perfectly anti-oriented on closest neighboring atoms, meaning they’re a little bit canted. They’re not perfectly anti-oriented—they are mostly, but there’s a little bit of a twist. And that little offset is significant because it’s part of what gives rise to the interesting effects in the project.”

That’s what gives this particular class of materials its name: Canted antiferromagnet.  

Fiete said, “An emerging class of electronic devices, so-called “spintronics,” rely on the manipulation of electron spin to improve information processing capabilities in future technologies. Another related field, called spin caloritronics, focuses on “how you convert heat flow into the flow of magnetism, or spin flow, and ultimately into a voltage.”

Posted: May 23,2022 by Roni Peleg