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Magnetism and electronic structure in YBa 2 Cu 3 <mml:…

1991; American Physical Society; Volume: 44; Issue: 13 Linguagem: Inglês

10.1103/physrevb.44.7034

1095-3795

Barbara Szpunar, Vedene H. Smith,

Magnetic properties of thin films

The influence of oxygen content and magnetic ordering on the electronic structure in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6}$ and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ is examined. The main difference is the presence in the superconductor, 1:2:3 ${\mathrm{O}}_{7}$, of \ensuremath{\pi} states on O(2) atoms (in the Ba planes), which are possible carriers of the holes needed for superconductivity. They may also be responsible for the absence of antiferromagnetic ordering in the Cu(2)-O(3,4) planes. The calculated magnetic susceptibility in 1:2:3 ${\mathrm{O}}_{7}$ is in satisfactory agreement with experiment. The present calculations show that, for antiferromagnetic ordering of the copper magnetic moments in the Cu(2)-O plane and between the planes, a Slater gap opens in the neighborhood of the Fermi energy, and 1:2:3 ${\mathrm{O}}_{6}$ becomes semiconducting. The Cu(1) sites in both systems are not likely to form substantial local magnetic moments and thus probably are not directly involved in the mechanism for superconductivity. The possibility of an anharmonic effect due to magnetic interaction is discussed.