  The defects, the behavior of 3d electrons and the hyperfine interactions in
binary Fe-Al alloys with different Al contents have been studied by the
measurements of positron lifetime spectra, coincidence Doppler broadening
spectra of positron annihilation radiation and Mossbauer spectra. The results
show that on increasing the Al content in Fe-Al alloys, the mean positron
lifetime of the alloys increase, while the mean electron density of the alloys
decrease. The increase of Al content in binary Fe-Al alloys will decrease the
amount of unpaired 3d electrons; as a consequence the probability of positron
annihilation with 3d electrons and the hyperfine field decrease rapidly.
Mossbauer spectra of binary Fe-Al alloys with Al content less than 25at% show
discrete sextets, these alloys give ferromagnetic contribution at room
temperature. The M\"ossbauer spectrum of Fe70Al30 shows a broad singlet. As Al
content higher than 40 at%, the M\"ossbauer spectra of these alloys are
singlet, that is, the alloys are paramagnetic. The behavior of 3d electron and
its effect on the hyperfine field of the binary Fe-Al alloy has been discussed.
