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Local magnetic structure in fully and partially ordered V$_2$$X$Al Heusler alloys ($X$=Cr, Mn, Fe, Co, Ni)

Zhenyang Xie, Jitong Song, Yuntao Wu, Yuanji Xu, Fuyang Tian

TL;DR

The paper tackles the challenge of understanding magnetic ordering in V-based Heusler alloys across different lattice types and degrees of chemical order. It combines density functional theory with atomistic Monte Carlo simulations to extract exchange couplings and map magnetic phases, introducing the concept of magnetic motifs—V–X–V triangular pathways—to unify the magnetic behavior. The key finding is that the nearest-neighbor exchange $J_{ ext{V-}X}$ within these motifs dictates ground-state order, while $J_{X-X}$ modulates the Curie temperature, a framework that remains valid even in partially ordered structures. This motif-based perspective provides a predictive, design-oriented lens for tailoring high-temperature magnetic properties in Heusler systems and could guide future exploration of spintronic materials.

Abstract

Multicomponent Heusler alloys exhibit various magnetic properties arising from their diverse atomic compositions and crystal structures. Identifying the general physical principles that govern these behaviors is essential for advancing their potential in spintronic applications. In this work, we combine density functional theory with atomistic Monte Carlo simulations to investigate the magnetic ground states, finite-temperature magnetic transitions, and electronic structures of fully-ordered $L2_1$-, $XA$-type, and partially-ordered V$_2X$Al ($X=$ Cr, Mn, Fe, Co, Ni) Heusler alloys. We propose the concept of magnetic motifs, defined as V-$X$-V triangular pathway connected by the nearest-neighbor (NN) exchange interactions $J_{\mathrm{V-}X}$. Within this framework, the magnetic ground states and transition temperatures across the V$_2X$Al family can be consistently understood. The magnetic order is primarily governed by the NN $J_{\mathrm{V-}X}$ interactions in the triangular motifs, while the transition temperatures are additionally influenced by $J_{X-X}$ couplings. Furthermore, the magnetic motifs are still proven to be effective in our calculations on partially-ordered V$_2$$X$Al alloys from $L2_1$ to $XA$-type structures. Our results suggest that the concept of magnetic motifs provides a unifying principle for understanding magnetic ordering in V-based Heusler alloys and could serve as a candidate guide for exploring magnetism and designing advanced spintronic materials in a broader class of Heusler systems.

Local magnetic structure in fully and partially ordered V$_2$$X$Al Heusler alloys ($X$=Cr, Mn, Fe, Co, Ni)

TL;DR

The paper tackles the challenge of understanding magnetic ordering in V-based Heusler alloys across different lattice types and degrees of chemical order. It combines density functional theory with atomistic Monte Carlo simulations to extract exchange couplings and map magnetic phases, introducing the concept of magnetic motifs—V–X–V triangular pathways—to unify the magnetic behavior. The key finding is that the nearest-neighbor exchange within these motifs dictates ground-state order, while modulates the Curie temperature, a framework that remains valid even in partially ordered structures. This motif-based perspective provides a predictive, design-oriented lens for tailoring high-temperature magnetic properties in Heusler systems and could guide future exploration of spintronic materials.

Abstract

Multicomponent Heusler alloys exhibit various magnetic properties arising from their diverse atomic compositions and crystal structures. Identifying the general physical principles that govern these behaviors is essential for advancing their potential in spintronic applications. In this work, we combine density functional theory with atomistic Monte Carlo simulations to investigate the magnetic ground states, finite-temperature magnetic transitions, and electronic structures of fully-ordered -, -type, and partially-ordered VAl ( Cr, Mn, Fe, Co, Ni) Heusler alloys. We propose the concept of magnetic motifs, defined as V--V triangular pathway connected by the nearest-neighbor (NN) exchange interactions . Within this framework, the magnetic ground states and transition temperatures across the VAl family can be consistently understood. The magnetic order is primarily governed by the NN interactions in the triangular motifs, while the transition temperatures are additionally influenced by couplings. Furthermore, the magnetic motifs are still proven to be effective in our calculations on partially-ordered VAl alloys from to -type structures. Our results suggest that the concept of magnetic motifs provides a unifying principle for understanding magnetic ordering in V-based Heusler alloys and could serve as a candidate guide for exploring magnetism and designing advanced spintronic materials in a broader class of Heusler systems.

Paper Structure

This paper contains 10 sections, 2 equations, 7 figures, 3 tables.

Table of Contents

  1. INTRODUCTION
  2. METHODS
  3. RESULTS AND DISCUSSION
  4. Structural configuration and thermodynamic stability analysis of V$_2$$X$Al
  5. Magnetic orders of fully-ordered $L2_1$- and $XA$-V$_2$$X$Al
  6. Microscopic magnetic mechanism in $L2_1$- and $XA$-V$_2$$X$Al
  7. Magnetic transition temperature of $L2_1$- and $XA$-V$_2$$X$Al
  8. Effect of chemical disorder on magnetism of partially-ordered V$_2$$X$Al
  9. Electronic structures of fully-ordered V$_2$$X$Al
  10. CONCLUSION

Figures (7)

  • Figure 1: Crystal structures of V$_2X$Al ($X=$ Cr, Mn, Fe, Co, Ni) Heusler alloys. (a) Fully-ordered $L2_1$-type full-Heusler ($Fm\bar{3}m$). (b) Fully-ordered $XA$-type inverse-Heusler ($F\bar{4}3m$). (c) Schematic pathway from $L2_1$ to $XA$ through disorder. (d) Partially-ordered V$_2X$Al structure considered in this work.
  • Figure 2: (a) Formation energies of V$_2X$Al ($X=$ Cr, Mn, Fe, Co, Ni) Heusler alloys for the fully-ordered ($XA$, $L2_1$) and partially-ordered structural configurations. (b) Total energies of V$_2X$Al for the corresponding fully-ordered and partially-ordered structures.
  • Figure 3: Isotropic Heisenberg exchange parameters $J$ for V$_2X$Al compounds. (a, b) $J$ as a function of neighbor distance for $L2_1$-type V$_2$MnAl and V$_2$CrAl, respectively. (c) NN exchange coupling $J_{\mathrm{V-}X}$ in $L2_1$-type compounds with $X=$ Mn, Fe, Co, Ni. (d, e) $J$ as a function of neighbor distance for $XA$-type V$_2$MnAl and V$_2$CrAl, respectively. (f) NN exchange couplings $J_{\mathrm{V2-}X}$ and $J_{X-X}$ in $XA$-type compounds with $X=$ Mn, Fe, Co, Ni. Insets illustrate the triangular exchange pathways responsible for the observed magnetic orders.
  • Figure 4: (a) Temperature dependence of the normalized magnetic moments for V$_2X$Al compounds in $L2_1$-type V$_2X$Al ($X =$ Cr, Mn, Fe, Co, Ni). (b) Temperature dependence of the normalized magnetic moments for V$_2X$Al compounds in $XA$-type V$_2X$Al.
  • Figure 5: (a) Temperature dependence of the normalized magnetic moment in partially-ordered V$_2$MnAl. (b–e) NN magnetic exchange couplings $J_{\mathrm{V-}X}$ for (b) fully-ordered $L2_1$, (c) 75% $L2_1$, (d) 50% $L2_1$, and (e) 25% $L2_1$ partially-ordered structures.
  • ...and 2 more figures