Piezoelectric materials, which generate an electric current when compressed or stretched, are familiar and widely used; for example, lighters that spark when a switch is pressed, microphones, sensors, and motors. A material has been developed with a similar property, but for magnetism. This “piezomagnetic” material changes its magnetic properties when put under mechanical strain.

(Top) A piece of BaFe2As2 is stretched while magnetic measurements are taken (the copper wire coil is part of the NMR device). (Bottom) Atoms in a plane, with black arrows showing how magnetic spins lie in plane and point in opposite directions. Grey arrows show how the magnetic spin of atoms shifts as the material is stretched.

A barium-iron-arsenic compound (BaFe2As2) can act as a superconductor at temperatures of about 25 Kelvin when doped with small amounts of other elements. This type of iron-based superconductor is interesting because although it has to be kept cold to work, it could be stretched into wires or cables.

BaFe2As2 is a “nematic” crystal because its structure goes through a phase transition before it becomes superconducting. In the case of BaFe2As2, its crystal structure goes from a square to a rectangular configuration.

The material was studied by nuclear magnetic resonance (NMR) imaging while stretching it to force it into the rectangular configuration. The magnetic properties of BaFe2As2 changed as it was stretched.

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.

For more information, contact Andy Fell at This email address is being protected from spambots. You need JavaScript enabled to view it..