Crystallographic, electronic structure and magnetic properties of the GdTAl; T = Co, Ni and Cu ternary compounds

Single phase GdCoAl, GdCuAl and single crystal GdNiAl samples of good quali ty were synthesized. The electrical resistivity, magnetization and AC susce ptibility as a function of temperature revealed in all these compounds a fe rromagnetic ordering at 100, 83 and 60 K, respectively. A magnetic transiti on, probably to a non-colinear structure was observed in GdNiAl at 31 K as well as the presence of the third magnetic transition at 14 K, while in the GdCuAl compound an evidence of similar transition was found at 23 K. In Gd NiAl a transition between two different crystallographic phases of ZrNiAl-t ype was observed at 220 K. The transition was accompanied by rapid jumps of crystal lattice parameters and of the electrical resistivity. The structur e determined above and below the transition point showed significant change s of the Gd-Gd and Gd-Ni interatomic distances. The observed phase transiti on was attributed to the filling of the Brillouin zone by the electrons at the Fermi level and to the rearrangement of the interatomic bond lengths, r esulting in new density of states distribution and a lower density of state s at the Fermi level. This assumption is consistent with the observed chang e of the relaxation rate between Gd 4f moments and the conduction electron system. The XPS investigation revealed the essential role played by the 3d electrons of the transition metals in these compounds. As a consequence, di fferent contributions of d states to the valence band affect the structural , magnetic and transport properties of these compounds. (C) 2000 Elsevier S cience B.V. All rights reserved.