Magnetic shape-memory effects in La2-xSrxCuO4 crystals

TL;DR

This study reveals unexpected magnetic shape-memory effects in La2-xSrxCuO4, where magnetic fields induce crystal axis reorientation and twin boundary motion in an antiferromagnet, challenging conventional understanding of spin-lattice interactions.

Contribution

It demonstrates magnetic field-induced crystal reorientation and twin boundary motion in an antiferromagnetic cuprate, a phenomenon previously observed mainly in ferromagnetic shape-memory alloys.

Findings

Lightly-doped LSCO crystals align their b axis with magnetic field.

Resistivity and susceptibility show switching and memory effects.

Direct observation of crystal rearrangement via surface kinks.

Abstract

The magnetic field affects the motion of electrons and the orientation of spins in solids, but it is believed to have little impact on the crystal structure. This common perception has been challenged recently by ferromagnetic shape-memory alloys, where the spin-lattice coupling is so strong that crystallographic axes even in a fixed sample are forced to rotate, following the direction of moments. One would, however, least expect any structural change to be induced in antiferromagnets where spins are antiparallel and give no net moment. Here we report on such unexpected magnetic shape-memory effects that take place ironically in one of the best-studied 2D antiferromagnets, La2-xSrxCuO4 (LSCO). We find that lightly-doped LSCO crystals tend to align their b axis along the magnetic field, and if the crystal orientation is fixed, this alignment occurs through the generation and motion of crystallographic twin boundaries. Both resistivity and magnetic susceptibility exhibit curious switching and memory effects induced by the crystal-axes rotation; moreover, clear kinks moving over the crystal surfaces allow one to watch the crystal rearrangement directly with a microscope or even bare eyes.