Effect of electron localization in theoretical design of Ni-Mn-Ga based magnetic shape memory alloys

Zelený, Michal; Sedlák, Petr; Heczko, Oleg; Seiner, Hanuš; Veřtát, Petr; Obata, Masao; Kotani, Takao; Oda, Tetsuji; Straka, Ladislav

doi:10.1016/j.matdes.2021.109917

Cited by 15 publications

(13 citation statements)

References 71 publications

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“…Even a lower value of U = 1.8 eV was applied to Mn in works on doped Ni–Mn–Ga alloys in order to fit experiments on martensite phases 45 , 46 . The calculations with U on Mn larger than 1.2 eV correctly identify the five-layered modulated martensite (10M) as the ground state structure 47 while GGA predicts a theoretical four-layered 4O martensite as the most stable structure 48 . On the other hand, calculations using GGA 49 or U on Mn 46 , 47 fail to predict the cubic phase as a high magnetic moment structure at 0 K. It follows from Fig.…”

Section: Introductionmentioning

confidence: 87%

Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

Janovec

Zelený

Heczko

et al. 2022

Sci Rep

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We present calculations based on density-functional theory with improved exchange-correlation approaches to investigate the electronic structure of $$\hbox {Ni}_2$$ Ni 2 MnGa magnetic shape memory alloy prototype. We study the effects of hybrid functionals as well as a Hubbard-like correction parameter U on the structural, electronic and magnetic properties of the alloy. We show that the previously successful application of U on Mn should be extended by including U on Ni to describe the d localized electrons more accurately and in better agreement with experiments. The bonding interactions within this intermetallic alloy are analysed including the role of non-transition metal. We found that the strongest and most stabilizing bond is formed between the Ga–Ni pairs due to the delocalized s–s and p–s orbital hybridization. Our findings suggest that minimization of the over-delocalization error introduced by standard semi-local exchange-correlation functionals leads to a better description of the $$\hbox {Ni}_2$$ Ni 2 MnGa alloy. Furthermore we propose that the experimental total magnetic moment of Ni–Mn–Ga alloys could be increased after carefully selected heat treatment procedures.

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Section: Introductionmentioning

confidence: 87%

Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

Janovec

Zelený

Heczko

et al. 2022

Sci Rep

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“…Later, Koubský et al [ 76 ] found that moderate corrections provided the best agreement for the elastic constants. Moreover, a recent study [ 77 ] revealed that with even a small Hubbard correction, the 10M structure, having a nearly tetragonal lattice, is more stable than all other martensitic structures, including 4O. The same settings also improved the agreement between the theoretical calculations and the experiment results for both the lattice parameters and the elastic constants.…”

Section: Search For the Ground State Of Ni2mngamentioning

confidence: 74%

“…On the other hand, this review also showed that the gap between ab initio calculations and experimental data is narrowing in many aspects, which aids in more insightfully interpreting the experiments and stimulating further progress in calculations and ab initio theory in general. One clear example is the identification of the ground state of stoichiometric

{Ni}_{2} MnGa

, where the discovery of the spontaneous formation of two‐layer stacking [ 65 ] and the correct treatment of electron localization [ 77 ] led to a convincing agreement between the experimental observations and the theoretical predictions. In addition, the elastic constants of the NM martensite phase were accurately predicted by calculations [ 225,229 ] before they were determined experimentally; [ 187 ] similarly, a good match was achieved for Co‐ and Cu‐alloyed NM martensites with reduced

c / a

ratios.…”

Section: Discussionmentioning

confidence: 99%

“…[ 235,236 ] Hence, there is strong motivation to use the calculated elastic constants. As explained in Section 2, the model with the U ‐Hubbard correction [ 77 ] accurately predicted the 10M modulated martensite to be the lowest‐energy state for stoichiometric

{Ni}_{2} MnGa

. In addition to the crystal structure, the model enabled the monoclinic elastic constants of 10M to be determined by the stress–strain method.…”

Section: Interaction With External Forces: Elastic Constants and Mobi...mentioning

confidence: 99%

“…Surprisingly, while there are some relatively soft shearing modes, the lowest shear modulus is ≈18 GPa, which is stiffer than the minimum shear modulus reported for NM martensite. [ 77 ] Moreover, the softest shears do not correspond to the

a / b \leftrightarrow c

twinning paths; instead, they represent the shears along the

a \leftrightarrow b

path. The soft shear clearly does not explain the extremely high mobility, and it does not indicate any instability in the modulated unit cell with respect to the

a / b \leftrightarrow c

reorientation path.…”

Section: Interaction With External Forces: Elastic Constants and Mobi...mentioning

confidence: 99%

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Experimental Observations versus First‐Principles Calculations for Ni–Mn–Ga Ferromagnetic Shape Memory Alloys: A Review

Seiner

Zelený

Sedlák

et al. 2022

Physica Rapid Research Ltrs

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This review summarizes recent advances in first‐principles simulations of the structural, mechanical, and magnetomechanical properties of Ni–Mn–Ga‐based ferromagnetic shape memory alloys from the perspective of experimental characterization. It focuses on calculations that can capture the main features of the low‐temperature phases, particularly the appearance of spatial modulations, the occurrence of intermartensitic transitions, and the high mobility of the twin boundaries, which allows for magnetically induced reorientation. Although the calculations can only be used to interpret some of these features and are not yet ready to be used as a tool for designing new alloys with the required properties, the gap between experimental observations and simulations is narrowing. When experiments and theory are discussed together, new challenges arise for both. In addition, new results on first‐principles‐determined elastic constants of the 10M martensite of Ni–Mn–Ga are presented and discussed with respect to the high mobility of the twin boundaries.

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Shear Deformation of Non-modulated Ni2MnGa Martensite: An Ab Initio Study

Heczko,

Šesták,

Seiner

et al. 2024

Shap. Mem. Superelasticity

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The impact of shear deformation in $$(101)[10\overline{1}]$$ ( 101 ) [ 10 1 ¯ ] system of non-modulated (NM) martensite in Ni2MnGa ferromagnetic shape memory alloy is investigated by means of ab initio atomistic simulations. The shear system is associated with twinning of NM lattice and intermatensitic transformation to modulated structures. The stability of the NM lattice increases with increasing content of Mn. The most realistic shear mechanism for twin reorientation can be approximated by the simple shear mechanism, although the lowest barriers were calculated for pure shear mechanism. The energy barrier between twin variants further reduces due to spontaneous appearance of lattice modulation or, in other words, the nanotwins with thickness of two atomic planes. Such nanotwins appear also on the generalized planar fault energy (GPFE) curve calculated using a newly developed advanced procedure and exhibits even lower energy than the defect free NM structure. These nanotwin doublelayers are also basic building blocks of modulated structures and play an important role in intermartensitic transformation.

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Effect of electron localization in theoretical design of Ni-Mn-Ga based magnetic shape memory alloys

Cited by 15 publications

References 71 publications

Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

Localization versus delocalization of d-states within the $$\hbox {Ni}_{{2}}$$MnGa Heusler alloy

Experimental Observations versus First‐Principles Calculations for Ni–Mn–Ga Ferromagnetic Shape Memory Alloys: A Review

Shear Deformation of Non-modulated Ni2MnGa Martensite: An Ab Initio Study

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