Weak ferromagnetism and Raman scattering in Eu2−xPrxCuO4

Magnetization and Raman experiments performed in single crystals of Eu2-xPrxCuO4 (0 less than or similar to x less than or similar to 1) are interpreted in terms of local distortions within the CuO2 planes. We find that samples grown in Pt crucibles contain Pt impurities, that are partially responsible for these distortions. We observed: (i) the appearance of two forbidden Raman modes (fRM) and (ii) a weak-ferromagnetic (WF) component when the crystals are field cooled in the ab-plane. The WF component, the onset temperature where 3D long-range WF is first observed, T-WF, the coercive field, H-C, and the intensity of the fRM decrease as the Pt content decreases. For crystals with a similar Pt content, the above quantities are larger for samples with smaller lattice unit cell volume, V. The crystal with the highest Pt content and smallest V (x = 0) shows, for T --> 0, an average canted Cu moment of 5.5(3) x 10(-3) mu(B)/Cu. The intensity of the fRM decrease with T, suggesting that the number of distortions decrease as V expands. This is consistent with recent neutron diffraction results in Eu2CuO4, where a tetragonal to orthorhombic phase transition was observed at T less than or similar to 200 K. We concluded that the Pt impurities and/or the reduction of V beyond a critical value, V-c, are the origin of these orthorhombic distortions which in turn are responsible for the fRM and WF observed in these compounds. (C) 1998 Elsevier Science B.V. All rights reserved.