The effect of bcc/fcc phase preference on magnetic properties of AlₓCrFeCoNi high entropy alloys

Abstract

AlxFeNiCrCo (0 ≤ x ≤ 1:5) high entropy alloys (HEA) have been studied both experimentally and theoretically, considering the multi-phase character of investigated samples. Magnetic properties of these alloys (ordering temperatures and average magnetic moments) were determined from magnetization measurements (VSM), being found strongly dependent on Al content. Decomposition of this HEA system into phases with different stoichiometries and different crystal structures was analyzed using electronic structure calculations by the KKR and KKR-CPA methods, and discussed in terms of total energy balance. Additional energy lowering was achieved by admitting atoms separation in Al- and Ni-rich bcc-phase within B2-like crystal structure, and in consequence ordering of some elements constituting HEA, has been determined. Accounting for all experimentally detected phases in AlxFeCrNiCo samples, it was found that calculated total and site-decomposed magnetic moments strongly depended on stoichiometries, more particularly on crystal structures. Comparison of KKR calculations based on ordered supercell models and KKR CPA results performed for fully disordered model of HEA systems, clearly indicates strong influence of local atoms neighborhood on magnetic moments. It is observed that in spite of increase of nominal Al content in AlxFeNiCrCo HEA, the actual concentration of Al in the detected fcc and bcc phases only slightly changes. Hence the strong measured variation of saturated magnetization with x is essentially driven by relative phase contributions. On the whole, much better agreement between measured and theoretical magnetic moments was obtained when averaging computational results obtained for experimentally detected phases and their contri butions, than KKR-CPA results achieved for single-phase HEAs with nominal compositions.