The magnetic state of Cu in the CuO₂-bilayers of PrBa₂Cu₃O_6+x: An NMR-investigation

Abstract

The antiferromagnetic state in the CuO₂-bilayers of PrBa₂ Cu₃O_6+x is usually assumed to be similar to the one in YBa₂Cu₃O₆. One evidence for this is the similarity of the NMR-spectra of the Cu(2)-sites (planes) in both materials. We reinvestigated the NMR-spectra in PrBa₂Cu₃O_6+x-crystals and observed below 2 K two additional, broad peaks centered roughly at 110 and 250 MHz. The signal is only present after applying a field larger than 5 T below 2.0 K. The frequency and temperature dependence of the relaxation rates allows us to ascribe the signal to the Cu(2)-sites. The signal vanishes irreversibly above 2.0 K and reversibly in fields above 0.5 T. Its intensity versus field shows at all frequencies a narrow peak near −0.2 T, for the field antiparallel to the one inducing the state, which shows the presence of a net polarisation of the spin system.