Polycrystalline pure Gd and Gd1-xLax (x = 0.15, 0.25, 0.27 and 0.50) alloys
have been studied by low field magnetic susceptibility (chi(AC)). magnetiz
ation and electrical resistivity measurements. Measurements were also perfo
rmed on samples with low demagnetizing factor geometry in order to study th
e ground state properties of these systems. For hexagonal close-packed (hcp
) samples the effect of spin reorientation is indicated by a broad peak in
the susceptibility curve and it shifts rapidly to lower temperatures with i
ncreasing La content in Gd metal. The spin reorientation effect is not obse
rved in the samples with La concentration higher than 15%. The chi(AC) and
resistivity measurements indicate a ferromagnetic transition at T-C = 225 K
for 15% La concentration. For the Sm-type structure sample, with x = 0.27,
two magnetic transition peaks are observed at 135 K and 113 K and helical
antiferromagnetic order is suggested. Finally, the results for the x = 0.50
alloy with double hexagonal close-packed (dhcp) crystalline structure indi
cate a spin-glass magnetic phase type, below T-g = 30 K. Observed magnetiza
tion remanent effects, in this latter case, give additional support for the
presence of the spin-glass phase.