Magnetic ordering of Pr and Cu in TlBa2PrCu2O7-y.

Neutron-scattering measurements have been performed to study the magnetic ordering of Pr and Cu in semiconducting ${\mathrm{TlBa}}_{2}$${\mathrm{PrCu}}_{2}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{y}}$. This compound has a nuclear structure which is similar to that of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ but with the CuO-chain layers fully replaced by TlO layers. At low temperatures the magnetic diffraction pattern reveals magnetic Bragg peaks of the {1/21/21/2} type, which are associated with the antiferromagnetic ordering of the Pr moments. The magnetic structure consists of nearest-neighbor spins along all three crystallographic directions being antiparallel. The spin direction is along the c axis, with a saturated moment of 1.05${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. The temperature dependence of the intensity of these reflections indicates a N\'eel temperature ${\mathit{T}}_{\mathit{N}}$\ensuremath{\approxeq}8 K, which is about half that observed in the related ${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ system. A second set of magnetic reflections, of the {1/21/21} type, are also observed, and these are associated with the Cu magnetic sublattice. This magnetic structure is identical to the ``plane ordering'' observed in the related 1:2:3 system, where the nearest-neighbor Cu spins are again antiparallel. The spin direction is in the tetragonal ab plane, with a saturated ordered moment of 0.59${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. The temperature dependence indicates a N\'eel temperature of \ensuremath{\approxeq}370 K for the Cu spins.