Raman-scattering and weak-ferromagnetism studies inEu2CuO4

Abstract

We show that there is a subtle instability of the ${\mathit{T}}^{\prime }$ structure for the ${\mathit{R}}_2$ ${\mathrm{CuO}}_4$ (R=rare earth) compounds at the center of the R series with the boundary at ${\mathrm{Eu}}_2$ ${\mathrm{CuO}}_4$. Crystals grown in Pt crucibles and PbO flux show weak ferromagnetism (WF) and two strongly temperature-dependent forbidden Raman peaks. However crystals grown in alumina crucibles and CuO flux do not show WF and the forbidden Raman peaks are much less intense. The observation of WF and forbidden Raman peaks for ${\mathrm{Eu}}_2$ ${\mathrm{CuO}}_4$ compounds suggests that the instability of the ${\mathit{T}}^{\prime }$ structure may be associated with O(1) displacement in the ${\mathrm{CuO}}_2$ planes. © 1996 The American Physical Society.