Simultaneous magnetic ordering of the Gd and Cu subsystems in oxygen-deficient GdBa2Cu3O6+x.

Abstract

The simultaneous ordering of Gd and Cu magnetic moments was investigated in oxygen-deficient ${\mathrm{GdBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$ (x\ensuremath{\approxeq}0.3). The internal magnetic fields measured by the muon-spin-rotation technique show strong deviations from a mere superposition of the magnetic fields produced by the two magnetic subsystems separately. Above the ordering temperature (${\mathit{T}}_{\mathit{N}}$=2.3 K) of the Gd moments an increased relaxation rate and a negative frequency shift compared to the behavior of the ordered Cu system alone are observed. These deviations indicate the persistence of long-lived Gd spin fluctuations up to a temperature of approximately 100 K. The observed negative frequency shift is attributed to an interaction of the Gd moments with the Cu(II) magnetic subsystem.