Observation of Pr magnetic order in PrBa2Cu3O7

Neutron-diffraction experiments have been carried out to investigate the magnetic order in PrBa2Cu3O7. Our neutron data indicate that the Cu spins order above 300 K. This ordering is not Significantly affected at low temperatures, where new magnetic Bragg peaks develop below 17 K that must be associated with the antiferromagnetic ordering of Pr spins, with an ordered moment of 0.79(5)mu(B). This rules out the possibility recently proposed by Nehrke and Pieper [Phys. Rev. Lett. 76, 1936 (1996)] that the new magnetic Bragg peaks arise from a spin reorientation of the Cu spins and that the Pr carries essentially no moment.