Structure and transport properties of the R2Co2Al compounds (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y)

Abstract

Abstract The new R2Co2Al compounds (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y), studied by single crystal and powder X-ray diffraction, crystallize with the W2CoB2 structure type. Pr2Co2Al is dimorphic, showing also its own monoclinic structure (a=9.595 Å, b=5.602 Å, c=7.753 Å, β=103.89°), which is closely related to the W2CoB2 type. Both structures are based on different packing of chains of cobalt-centred double trigonal prisms formed by rare earth and aluminum atoms. The electrical resistivity, measured in the 13-300K temperature range for all phases (save Y2Co2Al), always shows a transition point at temperatures going from 14K for Tm2Co2Al to 94K for Tb2Co2Al. As already found for Gd2Co2Al, these points should correspond to an order-disorder magnetic transition, and the deviations from de Gennes scaling indicate the influence of both the crystalline electric field and the strong coupling between 4f and conduction electrons.