4f-Electric quadrupolar effects on the lattice constants and magnetism of RCu₂Ge₂ (R=rare-earths)

Abstract

The temperature dependence of the lattice constants of the alloys, RCu₂Ge₂ (R=Nd, Tb, Dy, Ho and Tm) shows the existence of a lattice strain due to the alignment of the 4f-electric quadrupole at low temperatures. This strain could be related to the deviation of the Neel temperatures (T_N) from that predicted by de Gennes scaling, thereby indicating the role of the quadrupole on the magnetism. On the other hand, in PrCu₂Ge₂, for which the enhancement of T_N is the largest in this R series, the lattice constants interestingly behave as if the 4f-quadrupole moment is almost quenched and the anomalous magnetism in this case is attributed to some degree of 4f-delocalisation.