[Paper Review] Impact of local arrangement of Fe and Ni in Fe-Ni-Al Heusler alloys on the phase stability and magnetocrystalline anisotropy

V. V. Sokolovskiy, О. Н. Мирошкина+2 more|arXiv (Cornell University)|Jul 19, 2021

Heusler alloys: electronic and magnetic properties4 citations

TL;DR

This study uses density functional theory with supercell calculations to investigate how Fe and Ni atomic arrangements affect phase stability and magnetocrystalline anisotropy (MAE) in Fe₂Ni₁₊ₓAl₁₋ₓ Heusler alloys. It finds that the Fe/Ni alternated cubic structure in Fe₂NiAl exhibits the highest uniaxial MAE—twice that of tetragonal L1₀ FeNi—while Ni doping at the Al site reduces MAE and induces phase decomposition into Fe₂NiAl and FeNi phases.

ABSTRACT

On the basis of the density functional calculations in combination with the supercell approach, we report on a complete study of the influences of atomic arrangement and Ni substitution for Al on the ground state structural and magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss systematically the competition between five cubic Heusler-type structures formed by shuffles of Fe and Ni atoms to reveal routes for improving the phase stability and magnetic properties, in particular magnetocrystalline anisotropy~(MAE). We predict that in case of Fe$_2$NiAl the ground state cubic structure with alternated layers of Fe and Ni possesses the highest uniaxial MAE which twice larger than that for the tetragonal L1$_0$ FeNi. The successive Ni doping at Al sublattice leads to a change of ground state structure and to reduce of the MAE. In addition, the phase stability against the decomposition into the stable systems at finite-temperatures is discussed. All~Ni-rich Fe$_2$Ni$_{1+x}$Al$_{1-x}$ are turned to be decomposed into a dual-phase consisting of Fe$_2$NiAl and FeNi.

Motivation & Objective

• To understand how local atomic arrangements of Fe and Ni influence the structural and magnetic stability in Fe₂Ni₁₊ₓAl₁₋ₓ Heusler alloys.
• To identify the optimal Fe/Ni ordering configurations that maximize magnetocrystalline anisotropy (MAE) for potential spintronic applications.
• To evaluate the thermodynamic stability of these alloys against decomposition at finite temperatures.
• To determine the structural evolution and magnetic property changes upon Ni substitution at the Al sublattice.
• To clarify the competition between five cubic Heusler-type structures arising from Fe/Ni shuffling.

Proposed method

• Employing density functional theory (DFT) with the generalized gradient approximation (GGA) to compute electronic and magnetic properties.
• Using the supercell approach to model various atomic configurations of Fe and Ni on the cubic Heusler lattice, including ordered and disordered arrangements.
• Calculating the total energy and formation energy of different supercells to assess phase stability and identify ground state structures.
• Computing magnetocrystalline anisotropy energy (MAE) via the force theorem and non-collinear spin treatment to evaluate anisotropy contributions.
• Analyzing finite-temperature stability using thermodynamic models to predict decomposition behavior into equilibrium phases.
• Comparing the MAE of the cubic Fe/Ni alternated structure with the tetragonal L1₀ FeNi phase to quantify anisotropy enhancement.

Experimental results

Research questions

• RQ1 Which Fe/Ni atomic arrangement in Fe₂NiAl yields the highest magnetocrystalline anisotropy (MAE) among the five cubic Heusler-type structures?
• RQ2 How does Ni doping at the Al sublattice affect the ground state structure and MAE in Fe₂Ni₁₊ₓAl₁₋ₓ alloys?
• RQ3 What is the thermodynamic stability of Ni-rich Fe₂Ni₁₊ₓAl₁₋ₓ alloys at finite temperatures, and do they decompose into other phases?
• RQ4 How does the MAE of the Fe/Ni alternated cubic structure compare quantitatively to that of the tetragonal L1₀ FeNi phase?
• RQ5 What are the dominant decomposition products of Fe₂Ni₁₊ₓAl₁₋ₓ alloys under thermodynamic equilibrium?

Key findings

• The Fe/Ni alternated cubic structure in Fe₂NiAl exhibits the highest uniaxial magnetocrystalline anisotropy (MAE), which is twice that of the tetragonal L1₀ FeNi phase.
• Ni substitution at the Al sublattice leads to a structural transition from the cubic phase to a dual-phase mixture, with Fe₂NiAl and FeNi as the dominant decomposition products.
• All Ni-rich compositions (Fe₂Ni₁₊ₓAl₁₋ₓ) are thermodynamically unstable at finite temperatures and decompose into Fe₂NiAl and FeNi phases.
• The MAE decreases progressively with increasing Ni content at the Al site due to reduced structural and magnetic anisotropy.
• The ground state structure of Fe₂NiAl is stabilized by Fe/Ni ordering, with the alternated layer configuration being energetically most favorable.
• The study identifies a clear trade-off between phase stability and high MAE, where optimal MAE is achieved in the ordered cubic Fe₂NiAl phase but is compromised upon Ni doping.