Relationship between chemical bonding state and magnetostriction in Fe–Al–N alloy system

N atoms are added to Fe100−xAlx (x=10.0, 20.0, and 30.0 at. %) alloys to form preferential Al–N bonding in crystal lattice and then to reduce their magnetostriction. Single-crystal (Fe100−xAlx)1−0.01yNy(001) film samples (y ≤ 11.0 at. %) are employed to investigate the fundamental magnetic properties. bcc-based disordered A2 phase is formed for x = 10.0 and 20.0, whereas ordered B2 phase is involved for x = 30.0. As a result, the N content dependences of magnetocrystalline anisotropy and magnetostriction for x = 30.0 are different from those for x = 10.0 and 20.0. Low magnetocrystalline anisotropy constants, K1, on the order of 105 erg/cm3 are obtained for x = 10.0 and 20.0, even when N atoms are added. The saturation magnetostrictive coefficients along [100] direction, λ100, for x = 10.0 and 20.0 drastically decrease from +33.7 × 10−6 to +15.5 × 10−6 and from +64.9 × 10−6 to +16.4 × 10−6 with increasing the N content, respectively. The reduction is possibly attributed to bonding of N atoms placed at octahedral interstitial sites with Al atoms located at substitutional sites along 〈100〉 directions. On the other hand, the magnetostrictive coefficients along [111], λ111, for x = 10.0 and 20.0 do not almost vary depending on the N content in ranges between −18.4 × 10−6 and −17.0 × 10−6 and between −16.9 × 10−6 and −6.5 × 10−6, respectively. The magnetostrictive values of randomly-oriented polycrystalline materials, λrandom, are also estimated by using the relation of λrandom = (2/5)λ100 + (3/5)λ111. Low λrandom values on the order of 10−6 are achieved in ranges of y ≥ 0 for x = 10.0 and y ≥ 3.2 for x = 20.0. The present study has shown that reducing in magnetostriction of Fe–Al alloy to the order of λrandom = 10−6 while keeping low magnetocrystalline anisotropy is possible by N atom addition and control of its chemical bonding state.