Low temperature crystal structure of Ni–Mn–Ga alloys

Wedel, B.; Suzuki, Mitsuaki; Murakami, Yoshihiro; Wedel, C.; Suzuki, T.; Shindo, Daisuke; Itagaki, Kimio

doi:10.1016/s0925-8388(99)00198-x

Cited by 126 publications

(83 citation statements)

References 10 publications

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“…The structure and lattice constants from Rietveld refinement of the XRD pattern agree with Refs. [17,18]. DSC, resistivity, ac susceptibility and magnetization measurements are in agreement with literature.…”

supporting

confidence: 89%

Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

Biswas

Rawat

Barman

2005

Applied Physics Letters

145

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5% negative magnetoresistance (MR) at room temperature has been observed in bulk Ni2+xMn1−xGa. This indicates the possibility of using Ni2+xMn1−xGa as magnetic sensors. We have measured MR in the ferromagnetic state for different compositions (x=0–0.2) in the austenitic, premartensitic, and martensitic phases. MR is found to increase with x. While MR for x=0 varies almost linearly in the austenitic and premartensitic phases, in the martensitic phase it shows a cusplike shape. This has been explained by the changes in twin and domain structures in the martensitic phase. In the austenitic phase, which does not have twin structure, MR agrees with theory based on s-d scattering model.

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supporting

confidence: 89%

Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

Biswas

Rawat

Barman

2005

Applied Physics Letters

145

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“…This pattern can be indexed to a body centered tetragonal structure (I 4 /mmm) 16 or to a face centered orthorhombic structure (F mmm) with a = b 1 . It may be noted here that the tetragonal and orthorhombic structural models are related to each other by a simple transformation matrix 17 . In the orthorhombic structural model only the lattice parameters change from that of cubic high temperature phase but the relative atom coordinates remain unchanged.…”

Section: Methodsmentioning

confidence: 99%

Resistivity and thermopower of Ni2.19Mn0.81Ga

et al. 2004

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In this paper, we report results of the first studies on the thermoelectric power (TEP) of the magnetic heusler alloy Ni2.19Mn0.81Ga. We explain the observed temperature dependence of the TEP in terms of the crystal field (CF) splitting and compare the observed behavior to that of the stoichiometric system Ni2MnGa. The resistivity as a function of temperature of the two systems serves to define the structural transition temperature, TM , which is the transition from the high temperature austenitic phase to the low temperature martensitic phase. Occurrence of magnetic (Curie-Weiss) and the martensitic transition at almost the same temperature in Ni2.19Mn0.81Ga has been explained from TEP to be due to changes in the density of states (DOS) at the Fermi level.

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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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Low temperature crystal structure of Ni–Mn–Ga alloys

Cited by 126 publications

References 10 publications

Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

Large negative magnetoresistance in a ferromagnetic shape memory alloy: Ni2+xMn1−xGa

Resistivity and thermopower of Ni2.19Mn0.81Ga

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

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