Phase transition in the mixed crystals Tb p Y 1− p AsO 4

The energy of the four lowest crystal field levels of Tb 3+ in the mixed crystals Tb p Y 1− p AsO 4 is investigated in the range of the crystallographic and magnetic phase transition as a function of temperature and Tb‐concentration (0.2 < p ≦ 1). The results show that, in contrast to the magnetic ordering, the interaction causing the crystallographic transition is of long range and hence a simple molecular field theory fits the experimental data. For small Tb‐concentrations, the feature of this system are superimposed by effects of internal strains caused by the substitution of Tb 3+ by Y 3+ ions.