AbstractThe electronic structure and magnetisation of NiFeCoCr and NiFeCoCrPd high entropy alloys has been investigated. Using Ab-initio methods the momentum density of magnetic electrons and the magnetic structure of these alloys were determined. For this, special quasirandom structures and the coherent potential approximation were used for modelling the chemical disorder present in high entropy alloys. Also, magnetic Compton scattering experiments were done to validate the theoretical calculations.
The spin magnetic moment of NiFeCoCr and NiFeCoCrPd high entropy alloys
have been measured by magnetic Compton scattering. Both theoretical methods overestimated the spin magnetic moment as was expected in transition metals alloys for the local density approximation and generalised gradient approximation level of density functional theory. The magnetic structure in these alloys shown most of the spin magnetic moments of Cr aligned in a opposite direction to the magnetic moments of the other elements. Previous works reports clustering or short range order of Cr in NiFeCoCr high entropy alloy. Analysing its magnetic Compton profiles this possible clustering has been discarded. Then, a ferrimagnetic structure in the strict sense is not
possible in this compound.
Furthermore, the addition of Pd to NiFeCoCr high entropy alloy increased the spin magnetic moment of the resultant equiatomic alloy. The spin magnetic moment of NiFeCoCrPd high entropy alloy obtained by the special quasirandom structure method is close to the experimental value measured by magnetic Compton scattering.
|Date of Award||12 May 2020|
|Sponsors||SENESCYT Secretaría de Educación Superior, Ciencia|
|Supervisor||Stephen B Dugdale (Supervisor)|