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Anisotropic-Strain Control of The Magnetic Structure in Mn\textsubscript{3}GaN

Roman Malyshev, Ingeborg-Helene Svenum, Sverre M. Selbach, Thomas Tybell

TL;DR

This work studies how anisotropic in-plane strain influences the magnetic structure of Mn3GaN, an antiperovskite with frustrated noncollinear AFM order. Using density functional theory with VASP and PBEsol on a 2×2×2 supercell, the authors map a magnetic phase diagram under biaxial strain from $-5\%$ to $+5\%$, revealing transitions to ferro- and ferrimagnetic states and distorted noncollinear orders, with net moments tunable by strain direction. They show that not only equal biaxial strain but also mixed tensile/compressive and uniaxial strains can stabilize FM/FI phases and control magnetization direction, with first-order transitions and lattice changes accompanying the phase changes. These findings expand substrate options for Mn3GaN thin films and offer practical routes for strain-engineered spintronic devices.

Abstract

A first principles study is conducted to explore the changes in the magnetic structure of Mn\textsubscript{3}GaN under anisotropic biaxial strain. Mn\textsubscript{3}GaN is an antiperovskite with a structure similar to that of an ideal cubic perovskite. Several manganese nitride antiperovskites including Mn\textsubscript{3}GaN were reported to have a frustrated noncollinear antiferromagnetic structure. Successful electric switching of its magnetic structure has been reported. Furthermore, despite a cubic lattice symmetry, the magnetic symmetry is rhombohedral, allowing a piezomagnetic response. Tensile biaxial strain has been shown to produce a net magnetic moment by inducing in-plane spin canting. Compressive biaxial strain has been used to induce a spin-polarized ferro- or ferrimagnetic phase. In this study, anisotropic strain in the (001) plane is applied, outlining a magnetic phase diagram that can predict the properties when growing Mn\textsubscript{3}GaN thin films on noncubic substrates. The lattice vectors along the a and b crystallographic axes are strained by -5\% to 5\% in percentwise increments in all permutations. An extensive phase diagram is mapped, revealing multiple combinations of strain applied to the two lattice vectors that result in a ferro- or ferrimagnetic transition. Unlike previous results, not only strictly compressive strain on both lattice vectors, but combinations of tensile and compressive strain, as well as uniaxial strain, are seen producing the magnetic phase transitions. Furthermore, while biquadratic strain was seen producing a net moment in the [110] direction under tensile strain and [\bar{1}\bar{1}0] under compressive strain, anisotropic strain allows tuning the direction of the net magnetization.

Anisotropic-Strain Control of The Magnetic Structure in Mn\textsubscript{3}GaN

TL;DR

This work studies how anisotropic in-plane strain influences the magnetic structure of Mn3GaN, an antiperovskite with frustrated noncollinear AFM order. Using density functional theory with VASP and PBEsol on a 2×2×2 supercell, the authors map a magnetic phase diagram under biaxial strain from to , revealing transitions to ferro- and ferrimagnetic states and distorted noncollinear orders, with net moments tunable by strain direction. They show that not only equal biaxial strain but also mixed tensile/compressive and uniaxial strains can stabilize FM/FI phases and control magnetization direction, with first-order transitions and lattice changes accompanying the phase changes. These findings expand substrate options for Mn3GaN thin films and offer practical routes for strain-engineered spintronic devices.

Abstract

A first principles study is conducted to explore the changes in the magnetic structure of Mn\textsubscript{3}GaN under anisotropic biaxial strain. Mn\textsubscript{3}GaN is an antiperovskite with a structure similar to that of an ideal cubic perovskite. Several manganese nitride antiperovskites including Mn\textsubscript{3}GaN were reported to have a frustrated noncollinear antiferromagnetic structure. Successful electric switching of its magnetic structure has been reported. Furthermore, despite a cubic lattice symmetry, the magnetic symmetry is rhombohedral, allowing a piezomagnetic response. Tensile biaxial strain has been shown to produce a net magnetic moment by inducing in-plane spin canting. Compressive biaxial strain has been used to induce a spin-polarized ferro- or ferrimagnetic phase. In this study, anisotropic strain in the (001) plane is applied, outlining a magnetic phase diagram that can predict the properties when growing Mn\textsubscript{3}GaN thin films on noncubic substrates. The lattice vectors along the a and b crystallographic axes are strained by -5\% to 5\% in percentwise increments in all permutations. An extensive phase diagram is mapped, revealing multiple combinations of strain applied to the two lattice vectors that result in a ferro- or ferrimagnetic transition. Unlike previous results, not only strictly compressive strain on both lattice vectors, but combinations of tensile and compressive strain, as well as uniaxial strain, are seen producing the magnetic phase transitions. Furthermore, while biquadratic strain was seen producing a net moment in the [110] direction under tensile strain and [\bar{1}\bar{1}0] under compressive strain, anisotropic strain allows tuning the direction of the net magnetization.
Paper Structure (6 sections, 3 figures)

This paper contains 6 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Computational Method
  3. Results and Discussion
  4. Conclusion
  5. Acknowledgments
  6. Data Availability Statement

Figures (3)

  • Figure 1:
  • Figure 2:
  • Figure 3: Magnetic structures under strain with color-coding relative to Figure \ref{['fig:mag_phase_diagram']}. Distorted $\Gamma^{5g}$ ordering under (a) compressive and (b) tensile strain, (c) FM ordering (also collinear FI with antiparallel $\mathbf{m}_1$) and (d) noncollinear FI orderings under anisotropic strain. Relative LMM magnitudes not shown.