Ab-initio Study of the Physical Properties of Heusler Alloys
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Date
2021-11-14
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Abstract
Abstract :
Since their discovery, half-metallic ferromagnets have been the topic of many theoretical and
experimental researches due to their potential applications. The well-known Heusler
compounds have attracted most attention as several among them were predicted to be half
metals. The family of Heuslers incorporates thousands of members exhibiting diverse magnetic
phenomena, which makes them very useful in various contemporary fields such as spintronics.
For this reason, we have been interested in the ternary most explored group of Heusler alloys
as well as their quaternary daughter systems.
At first, we have investigated a set of Co- and Fe-based ternary systems (X = Fe, Co; Y = Zr,
Mo and Z = Ge, Sb) using ab-initio calculations. We found that Cu2MnAl type structure is more
favorable for all compounds, except X2MoGe (X = Co, Fe) and Co2MoSb where the inverse
structure was energetically more stable. After studying the electronic properties, we have
identified two half-metals (Co2ZrGe and Fe2ZrSb) that could be potential for spintronics
applications. Unlike Fe2ZrSb, the half-metallicity in Co2ZrGe alloy has already been predicted
in few theoretical studies where the structural and electronic properties agree well to our results.
We have also checked the mechanical properties of the ternary alloys. The elastic parameters
indicated the mechanical stability of the four Fe2ZrSb, Co2ZrGe and Fe2MoZ (Z = Ge, Sb)
materials, where the half-metallic Fe2ZrSb compound is the only one characterized by an
enhanced ductility.
Afterwards, we completed the previous study by forming eight quaternary structures using the
same previous magnetic components. We have studied the physical properties of the quaternary
XX’YZ alloys (X = Co, Fe; X’ = Mo, Fe; Y = Zr, Fe; Z = Sb, Ge) and explained their relation
with the former ternary Heuslers. The DFT method was once again applied to investigate the
magnetic nature of these alloys and we found two other half-metals (CoFeZrGe and CoFeZrSb).
Actually, both materials have already been investigated and the resulting lattice constants and
gaps were close in values to our theoretical calculations.
Additionally, we have computed the elastic parameters, electronic properties as well as the
thermoelectric efficiency of the quaternary XX’YZ alloys. They were found to be mechanically
stable and have shown different degrees of ductility and stiffness. Besides, they could be very
v
efficient for the thermoelectric field applications, which paves the way for further theoretical
and experimental investigations concerning these new Heuslers.
Description
Doctorat
