Scientists discover novel ‘piezomagnetic’ material

Piezoelectric materials, which generate an electric current when compressed or stretched, are familiar and widely used: think of lighters that spark when you press a switch, as well as microphones, sensors, motors and all kinds of other devices. Now a group of physicists has found a material with a similar property, but for magnetism. This ‘piezomagnetic’ material changes its magnetic properties when put under mechanical strain.

"Piezomagnetic materials are rarely found in nature, as far as I'm aware," said Nicholas Curro, professor of physics at the University of California, Davis and senior author of a paper on this discovery in Nature Communications.

Curro and colleagues were studying a barium-iron-arsenic compound, BaFe₂As₂, that can act as a superconductor at temperatures of about 25K (-248°C) when doped with small amounts of other elements. This type of iron-based superconductor is interesting because although it has to be kept pretty cold to work, it could be stretched into wires or cables.

BaFe₂As₂ is what is known as a ‘nematic’ crystal because its structure goes through a phase transition before it becomes superconducting. In the specific case of BaFe₂As₂, its crystal structure goes from a square to a rectangular configuration.

Curro and graduate students Tanat Kissikov and Matthew Lawson were attempting to study this material with nuclear magnetic resonance (NMR) imaging while stretching it, to see if they could force it into the rectangular configuration. To their surprise, the magnetic properties of BaFe₂As₂ changed as they stretched it.

The material is not a bulk magnet – the spins of its atoms point in alternating opposite directions, making it an antiferromagnet. But the direction of those magnetic spins does change in a measurable way when under stress, they found.

"The real surprise is that it appears that the direction of magnetism can change and come out of plane," Curro said.

According to Curro, there's no current theory to explain these results. His lab is looking to see if other materials can show the same behavior and if mechanical strain can also affect the material’s superconducting properties (these experiments were not carried out at temperatures where BaFe₂As₂ is a superconductor).

This discovery could lead to new ways to look for strain within materials such as aircraft components, Curro said.

This story is adapted from material from the University of California, Davis, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.