Dominance of the cubic laves phase in the GdTAl substitutional compounds

The GdFeAl compound contains 42.8 wt% of the cubic phase of the MgCu2 (Fd3m)-type and 57.2 wt% of the hexagonal phase of the MgZn2 (P6(3)/mmc)-type, the GdFeSi compound is a tetragonal of the CeFeSi (P4/nmm)-type phase, the GdCrAl and GdVAl compounds do not exist. In the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl substitutional compounds, the content of the cubic phase sharply increases and amounts to 62.3%, 99% and 99%, respectively, for the composition x = 0.2. The Curie temperature T-C(x) increases for the hexagonal and cubic phases in GdFeAl1-xSix, while for the tetragonal phase it decreases with increasing x. These various changes of T-C(x) are uniformly explained by the corresponding various changes of the density of states at the Fermi level N (E-F) in the model of exchange interaction between the R and 3d ions in R-3d intermetallics, in which T-c similar to N(E-F). Ab initio calculations of N(E-F) for the cubic, hexagonal and tetragonal phases in the GdFeAl1-xSix compounds have been carried out. The T-C(x) decreases in the GdFe1-xCrxAl and GdFe1-xVxAl systems for the hexagonal and cubic phases with increasing x. The saturation magnetization increases in the GdFeAl1-xSix, GdFe1-xCrxAl and GdFe1-xVxAl systems as x increases.