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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on MnNiGe by Materials Project

MnNiGe crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mn is bonded in a 5-coordinate geometry to six equivalent Ni and five equivalent Ge atoms. There are a spread of Mn–Ni bond distances ranging from 2.79–2.91 Å. There are a spread of Mn–Ge bond distances ranging from 2.54–2.63 Å. Ni is bonded in a 12-coordinate geometry to six equivalent Mn, two equivalent Ni, and four equivalent Ge atoms. Both Ni–Ni bond lengths are 2.64 Å. There are a spread of Ni–Ge bond distances ranging from 2.33–2.40 Å. Ge is bonded in a 9-coordinate geometry to five equivalent Mn and four equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnNiGe by Materials Project

MnNiGe crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mn is bonded in a 12-coordinate geometry to two equivalent Mn, six equivalent Ni, and six equivalent Ge atoms. Both Mn–Mn bond lengths are 2.65 Å. All Mn–Ni bond lengths are 2.71 Å. All Mn–Ge bond lengths are 2.71 Å. Ni is bonded in a 11-coordinate geometry to six equivalent Mn and five equivalent Ge atoms. There are three shorter (2.36 Å) and two longer (2.65 Å) Ni–Ge bond lengths. Ge is bonded in a 11-coordinate geometry to six equivalent Mn and five equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnNiGe by Materials Project

MnNiGe crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mn is bonded in a 11-coordinate geometry to five equivalent Ni and six equivalent Ge atoms. There are three shorter (2.39 Å) and two longer (2.70 Å) Mn–Ni bond lengths. All Mn–Ge bond lengths are 2.75 Å. Ni is bonded in a 5-coordinate geometry to five equivalent Mn and six equivalent Ge atoms. All Ni–Ge bond lengths are 2.75 Å. Ge is bonded in a 12-coordinate geometry to six equivalent Mn, six equivalent Ni, and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Controlling phase transitions in MnNiGe using thermal quenching and hydrostatic pressure

Here, the phase transitions in MnNiGe compounds were explored by manipulating the heat treatment conditions and through hydrostatic pressure application. As the quenching temperature increased, both the first-order martensitic structural transition temperatures and magnetic transition temperatures decreased relative to those in the slowly-cooled samples. When the samples were quenched from 1200 °C, the first-order martensitic structural transition temperature lowered by more than 200 K. The structural transitions also shifted to lower temperature with the application of hydrostatic pressure during measurement. Temperature-dependent x-ray diffraction results reveal that the changes of the cell parameters resulting from the structural transitions are nearly identical for all samples regardless of the extensive variation in their structural transition temperatures. In addition, neutron scattering measurements confirm the magnetic structure transition between simple and cycloidal spiral magnetic structures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effects of doping, hydrostatic pressure, and thermal quenching on the phase transitions and magnetocaloric properties in Mn 1– x Co x NiGe

The effects of doping, hydrostatic pressure, and thermal quenching on the phase transitions and magnetocaloric properties of the Mn 1–x Co x NiGe system have been investigated. Cobalt doping on the Mn site shifted the martensitic structural transition toward lower temperature until it was ultimately absent, leaving only a magnetic transition from a ferromagnetic (FM) to a paramagnetic (PM) state in the high-temperature hexagonal phase. Co-occurrence of the magnetic and structural transitions to form a first-order magnetostructural transition (MST) from the FM orthorhombic to the PM hexagonal phase was observed in samples with 0.05 < x < 0.20. An additional antiferromagnetic–ferromagnetic-like transition was observed in the martensite phase for 0.05 < x < 0.10, which gradually vanished with increasing Co concentration (x > 0.10) or magnetic field (H > 0.5 T). The application of external hydrostatic pressure shifted the structural transition to lower temperature until an MST was formed in samples with x = 0.03 and 0.05, inducing large magnetic entropy changes up to –80.3 J kg –1 K –1 (x = 0.03) for a 7-T field change under 10.6-kbar pressure. Similar to the effects of the application of hydrostatic pressure, an MST was formed near room temperature in the sample with x = 0.03 by annealing at high temperature (1200 °C) followed by quenching, resulting in a large magnetic entropy change of –56.2 J kg –1 K –1 . Furthermore, these experimental results show that the application of pressure and thermal quenching, in addition to compositional variations, are effective methods to create magnetostructural transitions in the MnNiGe system, resulting in large magnetocaloric effects.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗