Anomalous magnetic ordering in PrBa_2Cu_3O_{7-y} single crystals:   Evidence for magnetic coupling between the Cu and Pr sublattices
  In Al-free PrBa_2Cu_3O_{7-y} single crystals the kink in the temperature dependence of magnetic susceptibility chi_{ab}(T), connected with Pr antiferromagnetic ordering, disappears after field cooling (FC) in a field H || ab-plane. The kink in chi_c(T) remains unchanged after FC in H || c-axis. As a possible explanation, freezing of the Cu magnetic moments, lying in the ab-plane, caused by FC in H || ab, hinders their reorientation and, due to coupling between the Pr and Cu(2) sublattices, ordering of the Pr^{3+} moments. A field induced phase transition and a field dependence of the Pr^{3+} ordering temperature have been found for both H || c and H || ab. 
V.N. Narozhnyi, D. Eckert, K.A. Nenkov, G. Fuchs, T.G. Uvarova, and   K.-H. M\"uller