MAGNETIC TRANSITIONS IN PR2NIO4 SINGLE-CRYSTAL

The magnetic properties of a stoichiometric Pr2NiO4 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 T(N) = 325 K and T(cl) = 115 K, where the Pr ions are polarized by an internal magnetic field. At T(cl) a first modification of the magnetic structure occurs in parallel with a structural phase transition (Bmab to P4(2)/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(x) and g(x)c(y)f(z), respectively). A second magnetic transition having also a first-order character is also clearly identified at T(c2) = 90 K which corresponds to a spin reorientation process (g(x)c(y)f(z) to c(x)g(y)a(z) magnetic modes). It should be noted as well that the out-of-phase component of chi-ac 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 La2CuO4.