Dresden 2020 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 39: Computational Materials Modelling - Alloys I

MM 39.2: Talk

Wednesday, March 18, 2020, 16:00–16:15, BAR 205

Disorder driven stability in Co-based Heusler compounds — •Vitaliy Romaka, Ahmad Omar, Sabine Wurmehl, and Bernd Büchner — Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstr. 20, 01069 Dresden, Germany

Co-based Heusler compounds are known as promising half-metallic magnetic materials. However, their magnetic properties are affected by various factors, such as anti-site disorder, vacancies, and thermodynamic instability. Particularly in the case of systems that, in addition to Co, contain other 3d metals, for example Fe and/or Cr, the structural and thermodynamic issues are not very well understood. In order to shed light on the effects of structural disorder and off-stoichiometry in Co-based Heusler compounds, a section of the thermodynamic phase diagram for the quaternary Co-Cr-Fe-Al system was investigated by means of ab initio calculations. In the case of Co₂Cr_1−xFe_xAl solid solution, with energetically favorable B2-type structure, the shape of thermodynamic potential is quite similar to what is expected in the case of spinodal decomposition of the solid solution and is further characterized by two local minima at x ∼ 0.3 and 0.7, which describe the binodal region. Thermodynamic instability is also observed in the CoCr_1−xAl_x and CoFe_1−xAl_x solid solutions. Despite the fact that the quaternary composition Co₂Cr_0.5Fe_0.5Al is electronically equivalent to the thermodynamically stable Co₂MnAl phase, DFT modeling shows that the composition with higher Al content (∼Co₂Cr_0.3Fe_0.5Al_1.2) is energetically more stable, especially at high temperatures which is consistent with the experimental data.