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Structural and chemical disorder in Ni$_2$MnGa Heusler alloy investigated by nuclear magnetic resonance

Vojtěch Chlan, Martin Adamec, Oleg Heczko

Abstract

The local environment of Mn atoms in stoichiometric Ni-Mn-Ga Heusler alloys was investigated using Nuclear Magnetic Resonance (NMR) and interpreted with the help of Density Functional Theory (DFT) methods. In cubic austenite, the significant amount of structural defects was observed in \mn NMR experiments and interpreted using DFT calculations as individual antisite defects or defects accompanying anti-phase boundaries. Combined NMR and DFT analysis provides a consistent microscopic description of local disorder in Ni-Mn-Ga.

Structural and chemical disorder in Ni$_2$MnGa Heusler alloy investigated by nuclear magnetic resonance

Abstract

The local environment of Mn atoms in stoichiometric Ni-Mn-Ga Heusler alloys was investigated using Nuclear Magnetic Resonance (NMR) and interpreted with the help of Density Functional Theory (DFT) methods. In cubic austenite, the significant amount of structural defects was observed in \mn NMR experiments and interpreted using DFT calculations as individual antisite defects or defects accompanying anti-phase boundaries. Combined NMR and DFT analysis provides a consistent microscopic description of local disorder in Ni-Mn-Ga.

Paper Structure

This paper contains 6 sections, 1 equation, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Methods
  3. results and discussion
  4. Hyperfine field in $\mathrm{Ni}_2\mathrm{MnGa}$ - considerations
  5. Defects in Austenite $\mathrm{Ni}_2\mathrm{MnGa}$
  6. Conclusions

Figures (2)

  • Figure 1: $^{55}$Mn NMR spectrum of quenched and annealed Ni$_2$MnGa samples obtained in zero external magnetic field at room temperature.
  • Figure 2: Calculated austenite structures of Ni$_2$MnGa. (a) Ideal cell, (b) Mn$\leftrightarrow$Ga antisite (blue arrow), (c) one APB with ferromagnetic order, (d,e) two APBs with antiferromagnetic order. Red and yellow arrows highlight Mn orientations and nearest Mn neighbors.