Giant magneto-striction in TbCu2 and DyCu2 crystals

TbCu2 and DyCu2 undergo a conversion of the magnetic Ising axis from the cr ystallographic a- to the c-direction in magnetic field. The conversion fiel d is temperature dependent and has a minimum near the Neel temperatures 57 K (TbCu2) and 27 K (DyCu2). Magnetization and dilatometric experiments show that for both compounds the H-T-phase diagrams in a- and converted c-dircc tion are identical. At the axis conversion the crystal expands drastically in c and contracts in a by several percent. This can be viewed as a giant m agneto-striction (GMS). By neutron diffraction we find a transition from or thorhombic (virgin state) to hexagonal (converted state) crystal symmetry. In contrast, the magnetic propagation vector is the same for both states, i .e. (2/3 1 0). (C) 2000 Elsevier Science B.V. All rights reserved.