WEAK FERROMAGNETISM AND RAMAN-SCATTERING IN EU2-XPRXCUO4

Magnetization and Raman experiments performed in single crystals of Eu 2-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 ar e partially responsible for these distortions. We observed: (i) the ap pearance of two forbidden Raman modes (fRM) and (ii) a weak-ferromagne tic (WF) component when the crystals are field cooled in the ab-plane. The WF component, the onset temperature where 3D long-range WF is fir st observed, T-WF, the coercive field, H-C, and the intensity of the f RM decrease as the Pt content decreases. For crystals with a similar P t content, the above quantities are larger for samples with smaller la ttice 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, s uggesting that the number of distortions decrease as V expands. This i s 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 t he reduction of V beyond a critical value, V-c, are the origin of thes e orthorhombic distortions which in turn are responsible for the fRM a nd WF observed in these compounds. (C) 1998 Elsevier Science B.V. All rights reserved.