Influence of internal strains on the phase diagram of the metamagnet DyPO4

The (H, T) and (M, T) diagrams of the three-dimensional Ising-like antiferro-magnet DyPO₄ have been studied by magnetooptical rotation and light-scattering techniques. It is shown that the shapes of these diagrams depend on the nature and treatment of samples. By increasing the temperature, the discontinuity in magnetization ΔM does not decrease linearly to zero at a tricritical point but, instead, ΔM shows a pronounced tail. In addition, at higher temperatures, the metamagnetic transition seems to remain of very weak first order. Internal strains and magnetoelastic coupling can explain these results.