MAGNETIC ORDER OF PR IONS IN RELATED PEROVSKITE-TYPE PR123 COMPOUNDS

The magnetic order of Pr ions in polycrystalline, tetragonal PrBa2Cu3O 6.2 has been studied by neutron-diffraction measurements. The basic or dering consists of an antiferromagnetic arrangement with the propagati on vector k=[1/2, 1/2, 1/2], but the magnetic ordering is imperfect du e to finite correlation length xi(c) (10+/-1) angstrom along the c axi s. The Neel temperature is determined to be T(N)=(12+/-1) K, and the m agnetic saturation moment of the Pr ions turns out to be (1.9+/-0.2) m u(B). The distance Pr-O(2) compared in several related perovskite-type Pr compounds correlates with the Neel temperature in accordance with the superexchange interaction.