Crystal structure of 7M modulated Ni–Mn–Ga martensitic phase

Righi, Lara; Albertini, F.; Villa, Elena; Paoluzi, A.; Calestani, G.; Chernenko, V.A.; Besseghini, S.; Ritter, C.; Passaretti, Francesca

doi:10.1016/j.actamat.2008.05.010

Cited by 150 publications

(94 citation statements)

References 24 publications

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“…Interestingly, a similar incommensurate 7M modulated structure with almost unvaried q vector and modulation function has been found for Ni 2.15 Mn 0.85 Ga composition at room temperature [15]. The 7M modulation appears therefore, independently from the Ni-Mn-Ga composition, always featured by an incommensurate periodicity not reproduced by a seven-fold superstructure.…”

supporting

confidence: 71%

“…However this kind of studies supply a qualitative description of the structural modulation and our goal was the crystallographic description of the 7M modulated structure. Following the same procedure established for 5M family we studied off-stoichiometric NiMnGa samples by powder X-ray and neutron diffraction [15]. In particular the sample with composition Ni 2 Mn 1.2 Ga 0.8 is found to have a monoclinic unit cell a=4.222Å b=5.507Å c=4.267Å with β=93.3°at room temperature.…”

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confidence: 99%

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Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Righi

Albertini

Paoluzi

et al. 2009

MSF

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Abstract. Magnetic and structural properties in multifunctional FSMA (Ferromagnetic Shape Memory Alloys) belonging to Heusler family are frequently related to the occurrence of structural modulation in martensitic phases. The highest MFIS (Magnetic Field Induced Strain) effect has been observed in Ni-Mn-Ga alloys showing martensitic modulated structures. Depending on the composition, pressure and temperature conditions, this periodic structural distortion, consisting of shuffling of atomic layers along specific crystallographic directions, accompanies the martensitic transformation. Over the years, different modulated martensitic structures have been observed and classified depending upon the periodicity of corresponding superstructure (nM with n=3, 5, 6, 7, 12 etc). On the other hand, it has been demonstrated that in most cases such structural modulation is incommensurate and the crystal structure can be solved by applying superspace approach. The crystallographic representation of different modulated structures, obtained by structure refinement on powder diffraction data, suggests a unified description where every different "nM" periodicity can be straightforwardly represented. It will be presented an overview illustrating structural features of several displacive modulated martensitic lattices. For a specific Ni-Mn-Ga composition, the evolution of structural modulation upon temperature change will be illustrated.

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confidence: 71%

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confidence: 99%

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Righi

Albertini

Paoluzi

et al. 2009

MSF

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“…Remarkably, the crystallographic structure of the martensitic phase can be tuned by changing composition from modulated (commensurate and incommensurate) monoclinic 10M and 14M structures to non-modulated tetragonal [25][26][27]. Structural relationships between lattice parameters in the martensitic phase and austenitic and martensitic lattice parameters determine respectively the maximum possible strain achievable by magnetic field induced variant reorientation and by magnetic field induced transformation (MFIS) in single crystals.…”

Section: Introductionmentioning

confidence: 99%

Co and In Doped Ni-Mn-Ga Magnetic Shape Memory Alloys: A Thorough Structural, Magnetic and Magnetocaloric Study

Fabbrici

Porcari

Cugini

et al. 2014

Entropy

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Abstract:In Ni-Mn-Ga ferromagnetic shape memory alloys, Co-doping plays a major role in determining a peculiar phase diagram where, besides a change in the critical temperatures, a change of number, order and nature of phase transitions (e.g., from ferromagnetic to paramagnetic or from paramagnetic to ferromagnetic, on heating) can be obtained, together with a change in the giant magnetocaloric effect from direct to inverse. Here we present a thorough study of the intrinsic magnetic and structural properties, including their dependence on hydrostatic pressure, that are at the basis of the multifunctional behavior of Co and In-doped alloys. We study in depth their magnetocaloric properties, taking advantage of complementary calorimetric and magnetic techniques, and show that if a proper measurement protocol is adopted they all merge to the same values, even in case of first order transitions. A simplified model for the estimation of the adiabatic temperature change that relies only on indirect measurements is OPEN ACCESSEntropy 2014, 16 2205 proposed, allowing for the quick and reliable evaluation of the magnetocaloric potentiality of new materials starting from readily available magnetic measurements.

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“…There is an extreme sensitivity of the crystal structure of the martensitic phase with respect to composition in off-stoichiometric Ni 2+x Mn 1−x Ga or Ni 2 Mn 1+x Ga 1−x alloys [21,[24][25][26][27][28], showing that in dependence of composition and thermo-mechanical treatments, the crystal structure of low-temperature martensite can be tetragonal or monoclinic, with five-layered modulation (5M) [29], orthorhombic or monoclinic, with seven-layered modulation (7M) [30,31], or non-modulated tetragonal (NM) [32,33].…”

Section: Introductionmentioning

confidence: 99%

Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

Sokolovskiy

Grünebohm

Buchelnikov

et al. 2014

Entropy

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Abstract:The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations show the presence of the ferrimagnetic order of austenite and martensite depending on the composition, where the excess Mn atoms on Ga sites show reversed spin configurations. Stable ferrimagnetic martensite is found for systems with 0 (5) at% Co and a c/a ratio of 1.31 (1.28), respectively, leading to a strong competition of ferro-and antiferro-magnetic exchange interactions between nearest neighbor Mn atoms. The Monte Carlo simulations with ab initio exchange coupling constants as input parameters allow one to discuss the behavior at finite temperatures and to determine magnetic transition temperatures. The Curie temperature of austenite is found to increase with Co, while the Curie temperature of martensite decreases with increasing Co content. This behavior can be attributed to the stronger Co-Mn, Mn-Mn and Mn-Ni exchange coupling constants in austenite compared to the corresponding ones in martensite. The crossover from a direct to inverse magnetocaloric effect in Ni-Mn-Ga due to the substitution of Ni by Co leads to the appearance of a "paramagnetic gap" in the martensitic phase. Doping with In increases the magnetic jump at the martensitic transition temperature. The simulated magnetic and magnetocaloric properties of Co-and In-doped Ni-Mn-Ga alloys are in good qualitative agreement with the available experimental data.

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Crystal structure of 7M modulated Ni–Mn–Ga martensitic phase

Cited by 150 publications

References 24 publications

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Incommensurate and Commensurate Structural Modulation in Martensitic Phases of FSMA

Co and In Doped Ni-Mn-Ga Magnetic Shape Memory Alloys: A Thorough Structural, Magnetic and Magnetocaloric Study

Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

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