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Magnetic behavior of CoCrFeMnNi and derived high entropy alloys

Publication at Faculty of Mathematics and Physics, Central Library of Charles University |
2019

Abstract

The high entropy alloys represents the multi-principal element alloys with a nearly equimolar composition. Generally they are formed from at least five different elements.

It differs them from common alloys, where a few element dominates. Thanks to the high number of constituents one obtains a significant entropy contribution to the Gibbs free energy, which ensure the stabilization in high temperatures.

Besides, such number of constituents brings huge variability of their physical properties as well. Specific mechanical or electrical properties etc. can be mentioned.

It makes HEAs highly promising for application in the industry. One of the primary models of HEAs is well known CoCrFeMnNi, so-called 'Cantor alloys', which exhibits unique mechanical properties.

On the contrary the magnetism is highly suppressed there, despite of 3d magnetic elements. Therefore in our work we focus on their possible enhancement by varying chemical composition (substitution by Mo).

Also the influence of a particular element on the magnetic behavior is studied in details. The work is based on the ab-initio calculation, employing the TB-LMTO-ASA method.

Thanks to the used Green's function formalism we are able to treat the chemical disorder within the coherent potential approach. Moreover the Heisenberg magnetic exchange coupling were calculated by the Liechtenstein's formula.

Based on band structure calculation and obtained exchange interactions we will discuss the contribution of a particular elements to magnetic behavior same as the energetic stability (enthalpy of formation) of modified alloys. We will try to suggest the way, how the magnetism makes stronger.

Finally the magnetic ordering temperatures obtained by Monte-Carlo simulations are determined.