Antiferromagnetic ordering states of oxygen-deficient NdBa2Cu3O6+x and Nd1+yBa2-yCu3O6+x single crystals

E. Brecht, P. Schweiss, T. Wolf, A.T. Boothroyd, J.M. Reynolds, N.H. Andersen, H. Lutgemeier, W.W. Schmahl

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    The paper describes a study of the antiferromagnetic ordering of oxygen-deficient Nd1 + yBa2 - yCu3O6 + x single crystals. In pure, stoichiometric samples, y = 0, with different oxygen contents x in the Cu(1) plane (0.02<x<0.2), the antiferromagnetic I (AFI) phase appears to be stable down to 316 mK. The magnetic ordering within the Cu(2) sublattice of the pure NdBa2Cu3O6 + x system is therefore similar to that of the pure YBa2Cu3O6 + x parent compound. With increasing oxygen content, the Neel temperature drops significantly and the critical exponent changes from 0.26 for NdBa2Cu3O6.09 to about 0.5 for NdBa2Cu3O6.23. Magnetic ordering of the Nd3+ moments sets in at 1.7 K with a critical wave vector q(Nd) = (1/2 1/2 1/2). Reordering to the AFII phase is observed in a crystal, which has a significant amount (4%) of Nd3+ ions substituted on the Ba sites. The relatively high temperature T-2=95 K of this reordering suggests that the Nd3+ ions on Ba sites are very effective defects forcing the AFI<->AFII reordering. The mechanism of reordering is explained in terms of the creation of Cu2+ moments within the Cu(1) layer due to the Nd3+ ions on Ba sites, which via polarization lead to an effective ferromagnetic coupling between the moments on next-nearest neighboring Cu(2) layers. The Nd3+ doping on the Ba2+ sites increases the Neel temperature compared to the stoichiometric compound.
    Original languageEnglish
    JournalPhysical Review B Condensed Matter
    Issue number5
    Pages (from-to)3870-3878
    Publication statusPublished - 1999

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