Studies Of The Behavior Of 3d Electrons And Hyperfine Interaction In Binary Fe-Al Alloys

The microdefect,electron density and the Fe 3d-Al 3p interaction in binary Fe-Al alloys with difference chemical composition have been investigated by positron lifetime spectra and coincidence Doppler broadening spectra of positron annihilation radiation.The hyperfine interaction in ordered and disordered Fe-Al alloys has been charactered by analysing the Mossbauer spectra.The effects of microdefect,3d-3p interaction and hyperfine interaction on the brittleness and magnetic property of Fe-Al alloys have been discussed.The experimental results are as follows:(1)When Fe atoms and Al atoms are combined to form binary Fe-Al alloys, the 3d electrons of Fe atoms and 3p electrons of Al atoms are localized to form strong covalent bonds due to strong Fe 3d-Al 3p hybridization between nearest neighbor Fe-Al atom pairs.This leads to the decrease in the number of free electrons participating in the formation of metal bond,and reduce the probability of positron annihilation with 3d electrons. (2)The increase of Al content in binary Fe-Al alloys will enhance the 3d-3p interactions and weaken the d-d interactions;as a consequence the probability of positron annihilation with the 3d electrons of Fe atoms drops sharply.(3)The concentration of structure vacancies in binary Fe-Al alloy increases rapidly with the increase of Al content.(4)Mossbauer spectrum of binary Fe-Al alloy with Al content less than 25at%is a wide-spectrum with six peaks;while Mossbauer spectrum of binary Fe-Al alloy with Al content from 40 to 52 at%is a wide spectrum with single peak.The experimental results indicate that Fe₃Al with a DO₃-ordered structure is ferromagnetic while FeAl with a B2-ordered structure is nonmagnetic.The average magnetic moment per Fe atom in B2-ordered structure binary FeA1 alloy is zero.This is due to strong Fe 3d-Al 3p hybridization between nearest neighbor Fe-Al atom pairs in B2-ordered structure binary FeAl alloy and reducing the magnetic moment of Fe atom.(5)Mossbauer spectrum of FeAl powder,which are made from B2-ordered FeAl alloy having been ball-milled for 30h,is a wide-spectrum with multi peaks. This indicates that the magnetic moment of FeAl may increase by extensive disordering.