Temperature dependence of elastic properties of Ni<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math>Mn<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mrow /><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math>Ga and Ni<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display

Li, Chunmei; Luo, Hubin; Hu, Qing‐Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

doi:10.1103/physrevb.84.174117

Cited by 33 publications

(28 citation statements)

References 51 publications

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“…These quantities were in particular valence electron number, elastic constants, energy difference between austenite and the martensite phases ( E), etc. 5,8,[39][40][41][42] The valence electron number, e/a, i.e., the number of valence electron per atom has been identified to be closely related to T M in a large variety of Heusler alloys. The larger the e/a, the larger is the T M .…”

Section: Prediction Of the Martensite Transitionmentioning

confidence: 99%

Ab initiostudies of effect of copper substitution on the electronic and magnetic properties of Ni2MnGa and Mn2NiGa

et al. 2013

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Using first-principles density functional theory based calculations, we study systematically the effect of medium to large Cu substitution at the Mn, Ga as well as Ni sites on the geometric, bulk mechanical, electronic, and magnetic properties of Ni 2 MnGa and Mn 2 NiGa. The calculations have been carried out for possible austenite and martensite phases using a supercell approach. Partial Cu substitutions at Mn and Ga sites show promises in terms of the electronic and magnetic properties for both Ni 2 MnGa and Mn 2 NiGa alloys from an application point of view. Our calculations predict that for certain partial substitutions, the austenite to martensite transition temperature is likely to increase and the system remains magnetic in nature. On the other hand, a significantly large amount of Cu substitution at the Ni site seems to stabilize the austenite phase in both of these alloy systems rendering a martensite transition unlikely. Interestingly, the overall trend in the changes in the structural, bulk mechanical, electronic, and magnetic properties of these two different types of alloy systems, Ni 2 MnGa and Mn 2 NiGa, as a result of substantial Cu substitution in all the three different sites, is found to be the same.

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Section: Prediction Of the Martensite Transitionmentioning

confidence: 99%

Ab initiostudies of effect of copper substitution on the electronic and magnetic properties of Ni2MnGa and Mn2NiGa

et al. 2013

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“…Due to the short x-ray absorption length the exponential drop in intensity is expected for a transition moving into the crystal at a constant speed, and nucleated MT domains are known to grow at the speed of sound [16]. The speed of sound in the [100] direction of the modulated structure is estimated to be v ≈ 5 nm/ps [29]. A phase transition moving into the crystal at this speed would produce an exponential change in intensity with a time constant of ∼ 7 ps.…”

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confidence: 99%

Structural and magnetic dynamics in the magnetic shape-memory alloyNi2MnGa

et al. 2014

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Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni2MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300 fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320 fs, which is comparable to the quenching of the structural modulation.Multiferroic materials which exhibit large responses to electromagnetic and stress fields are of great interest for novel technical applications. To guide their rational design the microscopic origin of their functional properties must be understood which requires methods that can disentangle the interplay between electronic, magnetic and structural degrees of freedom. A prototypical example is the optimization of ferromagnetic X 2 YZ Heusler alloys, where one class shows novel functional properties such as magnetic shape memory and magnetocaloric effects due to the coexistence of ferromagnetism and a structural martensitic (MT) transition [1], and another class is half-metallic and suitable for spintronic applications [2]. Ni 2 MnGa is the classical Heusler magnetic shape memory alloy with a magnetically induced strain of up to 10% arising from the interplay between magnetic and structural domains in the twinned low temperature MT phase [1,[3][4][5]. The structure of the MT phase changes with alloy composition [6], but the modulated phases (commonly labelled 5M and 7M) [7, 8] displaying magnetic shape memory only exist if the MT transition temperature T MT is lower than the Curie temperature T C [6, 9]. In these structures the minimum in free energy is shifted such that the lattice constant ratio is c/a < 1 in the splitting (tetragonal or orthorhombic) of the high temperature cubic austenite (AUS) phase, compared to the usual global minimum found at c/a > 1 in the non-modulated tetragonal phase. Theoretical studies suggest that the modulation of the structure stabilizes this new minimum [10][11][12]. In Ni 2 MnGa compounds, we then have a situation where the interplay between an incommensurate structural modulation, a splitting of the electronic states due to the tetragonal or orthorhombic distortion of the cubic lattice and the ferromagnetic order combine to stabilize a phase displaying a large magnetic shape memory effect.In this letter we study this interplay by employing ultrafast time resolved x-ray and optical methods to separate the three types of order in time and to investigate the possible coupling between ferromagnetism and the modulated str...

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“…First of all, calculations of the static electronic susceptibility [15] suggest the contributions from the majority and minority spin are considerably different [16]. Since doping with Co is found to strongly affect both the total magnetic moment [32][33][34] as well as densities of states in the minority-and majority-spin channels [20,32], it is likely that the peak in the static electronic susceptibility is pushed from q max ð 4 7 ; 4 7 ; 0Þ towards the next major commensurability wave vector q max ð 1 2 ; 1 2 ; 0Þ. The impact of magnetism on the Fermi surface topology and the formation of modulated structures was studied also by ab initio methods [35,36].…”

mentioning

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Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

et al. 2015

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The origin of the martensitic transition in the magnetic shape memory alloy Ni-Mn-Ga has been widely discussed. While several studies suggest it is electronically driven, the adaptive martensite model reproduced the peculiar nonharmonic lattice modulation. We used femtosecond spectroscopy to probe the temperature and doping dependence of collective modes, and scanning tunneling microscopy revealed the corresponding static modulations. We show that the martensitic phase can be described by a complex charge-density wave tuned by magnetic ordering and strong electron-lattice coupling. DOI: 10.1103/PhysRevLett.115.076402 PACS numbers: 71.45.Lr, 78.47.-p, 81.30.Kf, 81.70.Fy Magnetic shape memory alloys present a new type of multifunctional materials, which display strong coupling between the magnetic and structural degrees of freedom. The ferromagnetic Ni-Mn-Ga alloy serves as a prototype system, displaying a giant 12% magnetic-field-induced strain in its low-temperature (T) martensitic phase (M phase) [1,2]. Since in Ni-Mn-Ga the M-phase transition can be tuned far above the room temperature by changing stoichiometry or doping [3,4], this alloy is of special technological interest [1,2,5].The rich phase diagram of Ni 2þxþy Mn 1−x Ga 1−y is characterized by a complex sequence of phase transitions. In its high-T (austenite) phase, Ni-Mn-Ga has a cubic L2 1 Heusler structure. At the M-phase transition temperature T M , the lattice undergoes a transformation, which can be described by a periodic shuffling of (011) planes along the ½011 direction [6]. Depending on the stoichiometry and the residual stress, the resulting low-T M phase is commonly found to have either tetragonal or orthorhombic symmetry, with a modulation period of ten (10M) or 14 (14M) atomic layers [6,7], respectively. For specific stoichiometries, e.g., Ni 2þx Mn 1−x Ga with x ≲ 0.1, a premartensitic phase (PM phase) is observed above T M [3] with the transition temperature T PM up to 50 K above T M [3,8]. In the PM phase, the lattice displays a harmonic threefold modulation with the wave vector q PM ¼ q max ð 1 3 ; 1 3 ; 0Þ. Inelastic neutron scattering studies of the high-T cubic phase [9] showed a dramatic softening of the TA-2 phonon branch at q PM , indicative of a Kohn anomaly. These observations [9][10][11][12], together with the observed opening of a pseudogap at T PM [8,13], suggest an electronic instability within the Peierls scenario to be driving the PM-phase transition. The observation of a phase mode in the 10M phase [14] also suggested the electronic instability. In fact, the electronic band structure studies [11,15,16] revealed the possible Fermi surface nesting conditions for all of the observed structural modulations. However, for the case of the 14M martensite, it was argued that the modulated phase can be constructed from nonmodulated martensitic unit cells [17,18]. This adaptive martensite scenario [17][18][19] recently received considerable attention.To determine which theory gives a more appropriate physical picture of the pha...

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Temperature dependence of elastic properties of Ni2+xMn1−xGa and Ni

Cited by 33 publications

References 51 publications

Ab initiostudies of effect of copper substitution on the electronic and magnetic properties of Ni2MnGa and Mn2NiGa

Ab initiostudies of effect of copper substitution on the electronic and magnetic properties of Ni2MnGa and Mn2NiGa

Structural and magnetic dynamics in the magnetic shape-memory alloyNi2MnGa

Collective Modes and Structural Modulation in Ni-Mn-Ga(Co) Martensite Thin Films Probed by Femtosecond Spectroscopy and Scanning Tunneling Microscopy

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