<i>Ab initio</i>Prediction of Martensitic and Intermartensitic Phase Boundaries in Ni-Mn-Ga

Dutta, Biswanath; Çakır, Aslı; Giacobbe, Carlotta; Al-Zubi, A.; Hickel, Tilmann; Acet, Mehmet; Neugebauer, Jörg

doi:10.1103/physrevlett.116.025503

Cited by 62 publications

(47 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…10 On decreasing temperature, modulated martensitic phases tend to transform to the non-modulated martensite structure which is more favorable energetically. 11,12 Additionally, the same materials also exhibit metastable behavior when temper-annealed at high temperatures.…”

mentioning

confidence: 99%

Shell-ferromagnetism in Ni-Mn-based Heuslers in view of ductile Ni-Mn-Al

Çakır

Acet

2017

AIP Advances

Self Cite

View full text Add to dashboard Cite

The present work deals with magnetic and structural phase instabilities in Ni-Mn-based Heusler alloys especially Ni-Mn-Al. The temper-annealed Ni50Mn45Al5 Heusler alloy decomposes into the full stoichiometric Ni2MnAl and NiMn phases. The decomposed stoichiometric Heusler forms precipitates in an anti-ferromagnetic NiMn matrix and exhibits shell-ferromagnetic properties when the temper-annealing is performed under magnetic field. The shell-ferromagnetism results from the magnetic proximity effect and is observed as vertically shifted magnetization loops. The presence of this property in Ni50Mn45Al5 adds the possibility of having a ductile material while preserving the shell-ferromagnetic properties.

show abstract

mentioning

confidence: 99%

Shell-ferromagnetism in Ni-Mn-based Heuslers in view of ductile Ni-Mn-Al

Çakır

Acet

2017

AIP Advances

Self Cite

View full text Add to dashboard Cite

show abstract

“…For off-stoichiometry composition the (10M →) 14M → NM sequences of intermartensitic transformations occur with decreasing temperature 32,33 . Recent ab initio calculations of the Ni 2 MnGa phase diagram which include lattice and vibrational degrees of freedom propose that the stability of martensite and intermartensitic transformation can be understood solely using thermodynamic concepts 31 . However, such predictions for low-temperature part of phase diagram are still uncertain due to the small structural energy difference between martensitic phases.…”

mentioning

confidence: 99%

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

et al. 2016

View full text Add to dashboard Cite

The ab initio electronic structure calculations of the Ni2MnGa alloy indicate that the orthorhombic 4O structure exhibits the lowest energy compared to all known martensitic structures. The 4O structure is formed by nanotwin double layers, i.e., oppositely oriented nanotwins consisting of two (101) lattice planes of nonmodulated martensitic structure. It exhibits the lowest occupation of density of states at the Fermi level. The total energy 1.98 meV/atom below the energy of nonmodulated martensite is achieved within structural relaxation by shifting Mn and Ga atoms at the nanotwin boundaries. The same atomic shift can also be found in other martensitic nanotwinned or modulated structures such as 10M and 14M, which indicates the importance of the nanotwin double layer for the stability of these structures. Our discovery shows that the nanotwinning or modulation is a natural property of low-temperature martensitic phases in Ni-Mn-Ga alloys.PACS numbers: 81.30. Kf, 71.15.Nc, 64.60.My Among Heusler alloys, the Ni 2 MnGa is one of the few, which exhibit the unique properties resulting in a giant magnetic field-induced strain (MFIS) in their lowtemperature martensitic phase 1 . The MFIS can reach up to 12 % in case of Co-and Cu-doped Ni 2 MnGa 2 . Important factors enabling the MFIS are large magnetocrystalline anisotropy and extraordinarily high mobility of martensite twin boundaries 3-6 that primarily depends on martensite structure. While at elevated temperature there is a single austenitic phase of Ni 2 MnGa with cubic L2 1 structure, several low-temperature martensitic phases have been observed depending on composition, temperature and applied stress 7-9 . Martensitic phases with orthorhombic or monoclinic structures exhibit modulation of (110) planes in [110] direction with the periodicity of ten or fourteen lattice planes (10M or 14M). The third martensitic phase with nonmodulated (NM) tetragonally distorted L2 1 structure is typical for larger deviation from stoichiometry. In addition, above the martensitic transformation temperature there is a cubic premartensite with the periodicity of six lattice planes (6M) in alloys with small deviation from stoichiometry 10 .Low-temperature instability of L2 1 austenite can be explained by a strong Fermi surface nesting responsible for the phonon softening in [110] direction, which explains structural modulation of 6M premartensite 11-14 . In addition there is also a large Ni-e g peak corresponding to antibonding states right below the Fermi level, E f , in the minority density of states (DOS) channel. Due to the band Jahn-Teller effect the L2 1 cubic structure lowers its symmetry, which pushes the peak above E f resulting in lower energy [15][16][17] . Nonetheless, the precise causes of the variety of observed low temperature martensitic phases and mechanism of intermartensitic transformations between them have not been fully explained yet.Ab initio calculations have been employed to understand modulations in Ni 2 MnGa. Early works used description of 10M and 14M m...

show abstract

“…The understanding of the martensitic transformation at such compositions requires a proper treatment of the coupling between the chemical and the other thermodynamic (phonons, magnons) degrees of freedom. Extending the concepts developed for stoichiometric Ni 2 MnGa further to the case of off‐stoichiometric compositions, we have explored the Mn‐rich part of the phase diagram (i.e., Ni 2 Mn 1+ y Ga 1− y ) . The Mn‐rich off‐stoichiometric composition has been achieved by considering one Mn antisite per supercell.…”

Section: Coupling On the Atomic Scalementioning

confidence: 99%

“…Near the stoichiometric composition, five‐fold modulated martensite (5 M c ) forms a phase boundary with the austenite (L2 1 ) whereas for larger Mn content, non‐modulated L1 0 martensite is in direct contact with the austenite phase. The calculated T M values show excellent agreement with the corresponding experimental results …”

Section: Coupling On the Atomic Scalementioning

confidence: 99%

Coupling Phenomena in Magnetocaloric Materials

et al. 2018

View full text Add to dashboard Cite

Strong coupling effects in magnetocaloric materials are the key factor to achieve a large magnetic entropy change. Combining insights from experiments and ab initio calculations, we review relevant coupling phenomena, including atomic coupling, stress coupling, and magnetostatic coupling. For the investigations on atomic coupling, we have used Heusler compounds as a flexible model system. Stress coupling occurs in first‐order magnetocaloric materials, which exhibit a structural transformation or volume change together with the magnetic transition. Magnetostatic coupling has been experimentally demonstrated in magnetocaloric particles and fragment ensembles. Based on the achieved insights, we have demonstrated that the materials properties can be tailored to achieve optimized magnetocaloric performance for cooling applications.

show abstract

Ab initioPrediction of Martensitic and Intermartensitic Phase Boundaries in Ni-Mn-Ga

Cited by 62 publications

References 38 publications

Shell-ferromagnetism in Ni-Mn-based Heuslers in view of ductile Ni-Mn-Al

Shell-ferromagnetism in Ni-Mn-based Heuslers in view of ductile Ni-Mn-Al

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

Coupling Phenomena in Magnetocaloric Materials

Contact Info

Product

Resources

About