Magnetic field induced Ising axis conversion in Tb0.5Dy0.5Cu2 single crystals

We study the Ising axis conversion in a mixed Tb0.5Dy0.5Cu2 single crystal. Interest is focused on how changes in the exchange interactions due to rar e earth substitutions influence the existence of magnetic phases and the cr itical field values for the Ising axis conversion. From magnetisation measu rements we determined the (H - T) phase diagram for magnetic fields paralle l to the easy a-axis and the temperature dependence of the critical field f or the Ising axis conversion. Both properties for the mixed crystal follow a,simple composition scaling behavior. But in contrast to previous studies on the pure compounds TbCu2 and DyCu2 the changes of magnetic and structura l properties at the conversion cannot be recovered completely by thermal tr eatment. Only a small part (10 % of the sample volume) goes back to the vir gin state after warming the sample to 500 K. This behavior is of great inte rest for further neutron or X-ray diffraction studies of the Ising axis con version allowing to study the converted phase under routinely used experime ntal conditions.