Magnetic phase transitions inGd2CuO4

We have made neutron-diffraction, magnetization, and antiferromagnetic-resonance investigations of ${\mathrm{Gd}}_2$ ${\mathrm{CuO}}_4$ single crystals. Neutron-diffraction experiments on ${}_{}{}^{158}{}_{}{}^{}\mathrm{enriched}$ ${\mathrm{Gd}}_2$ ${\mathrm{CuO}}_4$ single crystals show that the gadolinium atoms order antiferromagnetically at ${\mathit{T}}_{\mathit{N}}$=6.4 K with the propagation vector k=(0,0,0). The two Gd atoms of the primitive unit cell related by the center of symmetry are oppositely oriented. The antiferromagnetic-resonance spectra indicate that ${\mathrm{Gd}}_2$ ${\mathrm{CuO}}_4$ belongs to the class of ‘‘easy-plane’’ antiferromagnets and show the presence of a second-order reorientation phase transition at ${\mathit{H}}_{\mathit{c}}$=0.88 T (H∥[100], T=1.8 K). The magnetization measurements confirm the presence of this reorientation transition and also show a complete ferromagnetic alignment of Gd moments at H=11 T and T=1.5 K.