Magnetic transitions in Pr2Ni04 single crystal

The magnetic properties of a stoichiometric PrzNi04 single crystal have been examined by means of the temperature dependence of the complex ac susceptibility and the isothermal magnetization in fields up to 200 kOe at T = 4.2 K. Three separate phases have been identified’ and their anisotropic character has been analyzed. A collinear antiferromagnetic phase appears first between TN = 325 K and T,, = 115 K, where the Pr ions are polarized by an internal magnetic field. At T,, a first modification of the magnetic structure occurs in parallel with a structural phase transition (Bmab to P4$ncm). This magnetic transition has a first-order character and involves both the out-of-plane and the in-plane spin components (magnetic modes g, and g#Jn respectively). A second magnetic transition having also a first-order character is also clearly identified at Tc2 = 90 K which corresponds to a spin reorientation process (g&,JZ to cxgvaZ magnetic modes). It should be noted as well that the out-of-phase component of x== shows a peak around 30 K which reflects the coexistence of both magnetic configurations in a wide temperature interval. Finally, two field-induced transitions have been observed at 4.2 K when the field is directed along the c axis. We propose that the high-field anomaly arises from a metamagnetic transition of the weak ferromagnetic component, similarly to La$uOe