Magnetic shape memory effect in the paramagnetic state in RCu₂ (R=rare earth) antiferromagnets

RCu₂ (R=rare earth) is presented as the first magnetic shape memory (MSM) alloy with the magnetic anisotropy of rare earth ions as impelling force. Besides La_2–xSr_xCuO₄ RCu₂ is the second known antiferromagnetic MSM-compound system. However, longrange magnetic order is not necessary for the MSM effect here. Microstructural changes are occurring even above the magnetic ordering temperature because the magnetic anisotropy gives a strong effect also in the paramagnetic state. RCu₂ compounds have a pseudohexagonal orthorhombic structure which splits up into three twin variants, each rotated about 60° to the others about the pseudohexagonal axis. To move the twin boundaries, a magnetic field of about 3.2  T and a temperature of typical 30  K is necessary. Moving of twin boundaries results in a typical length change of two percent. Depending on the field direction a certain twin variant is favored. Neutron data from a Tb_0.5Dy_0.5Cu₂ single crystal confirm a change of the volume fraction of the three twin variants.

©2006 The American Physical Society