X-ray diffraction experiments at room temperature and magnetization measurements from 4.2 to about 1000°K have been performed on the whole composition range of Fe-Ru alloys. The magnetic susceptibility, χ, in the ε phase of 100 at% Ru to 13 at% Ru-Fe alloy shows a Pauli-paramagnetic temperature dependence at high temperatures with small negative and positive temperature coefficients for the alloys less than and more than 30 at% Ru, respectively. The value of χ at room temperature increases with increasing Fe concentration from 100 at% Ru ; the extrapolated value of χ, that is χ of the ε Fe, is as large as 10^/Oe/mole. The Fe-rich alloys in the ε phase shows some decrease in χ at low temperatures, suggesting the occurrence of metallic antiferromagnetic ordering. The reason for the variation in χ with Fe concentration may be attributed to the change in the density of states at the Fermi level due to the change of the width of the d-band, relative position of the Fermi level being unchanged because of the fixed number of outer electrons
