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 13-300 K temperature range for all phases (save Y2Co2Al), always shows a transition point at temperatures going from 14 K for Tm2Co2Al to 94 K 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.
Structure and transport properties of the R2Co2Al compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Y)
PANI, MARCELLA;MERLO, FRANCO;
2002-01-01
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 13-300 K temperature range for all phases (save Y2Co2Al), always shows a transition point at temperatures going from 14 K for Tm2Co2Al to 94 K 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.
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