Antiferromagnetic ordering of Cu ions in NdBa2Cu

Abstract

Neutron-scattering experiments performed on single crystals ${\mathrm{NdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.1}$ reveal antiferromagnetic order for T${T}_{N}$=385\ifmmode\pm\else\textpm\fi{}2 K in which the structure is characterized by the magnetic wave vector ((1/2,1)/2,(1/2); this had previously been observed only at low temperature in single crystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathrm{x}}$ [the Y(1:2:3) compound]. The magnetic intensities are accounted for by ${\mathrm{Cu}}^{2+}$ spins coupled antiferromagnetically in the ${\mathrm{CuO}}_{2}$ planes as in the yttrium compounds ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathrm{x}}$ (x0.5). However, unlike the Y(1:2:3) compound case, the oxygen-deficient planes in the Nd(1:2:3) compound exhibit small staggered magnetization \ensuremath{\epsilon}S which induces the spin ordering -S-\ensuremath{\epsilon}S-S+S+\ensuremath{\epsilon}S+S, along the tetragonal axis. The average staggered magnetization evaluated at room temperature is about 0.40${\ensuremath{\mu}}_{B}$ in the ${\mathrm{CuO}}_{2}$ planes while in the oxygen deficient (Cu-chain) layers it is about 0.04${\ensuremath{\mu}}_{B}$. The exchange coupling between the Cu atoms in the oxygen deficient layer containing Cu chains and its nearest-neighbor ${\mathrm{CuO}}_{2}$ layers (Cu planes) is thus ferromagnetic; this may be readily understood by consideration of the relevant ${\mathrm{Cu}}^{2+}$ orbitals.