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10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Lattice instability and magnetic phase transitions in strongly correlated MnAs

Using variable temperature x-ray total scattering in magnetic field, we study the interaction between lattice and magnetic degrees of freedom in MnAs, which loses its ferromagnetic order and hexagonal ('H') lattice symmetry at 318 K to recover the latter and become a true paramagnet when the temperature is increased to 400 K. Our results show that the 318 K transition is accompanied by highly anisotropic displacements of Mn atoms that appear as a lattice degree of freedom bridging the 'H' and orthorhombic phases of MnAs. This is a rare example of a lowering of an average crystal symmetry due to an increased displacive disorder emerging on heating. Furthermore, our results also show that magnetic and lattice degrees of freedom appear coupled but not necessarily equivalent control variables for triggering phase transitions in strongly correlated systems in general and in particular in MnAs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnAs by Materials Project

MnAs is Modderite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mn3+ is bonded to six equivalent As3- atoms to form a mixture of distorted edge, face, and corner-sharing MnAs6 octahedra. The corner-sharing octahedra tilt angles range from 44–59°. There are a spread of Mn–As bond distances ranging from 2.36–2.59 Å. As3- is bonded in a 6-coordinate geometry to six equivalent Mn3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnAs by Materials Project

MnAs is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mn3+ is bonded to six equivalent As3- atoms to form a mixture of corner, edge, and face-sharing MnAs6 octahedra. The corner-sharing octahedral tilt angles are 50°. All Mn–As bond lengths are 2.52 Å. As3- is bonded in a 6-coordinate geometry to six equivalent Mn3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnAs by Materials Project

MnAs is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mn3+ is bonded to four equivalent As3- atoms to form corner-sharing MnAs4 tetrahedra. All Mn–As bond lengths are 2.46 Å. As3- is bonded to four equivalent Mn3+ atoms to form corner-sharing AsMn4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu(MnAs)2 by Materials Project

EuMn2As2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Eu2+ is bonded to six equivalent As3- atoms to form EuAs6 octahedra that share corners with twelve equivalent MnAs4 tetrahedra, edges with six equivalent EuAs6 octahedra, and edges with six equivalent MnAs4 tetrahedra. All Eu–As bond lengths are 3.04 Å. Mn2+ is bonded to four equivalent As3- atoms to form MnAs4 tetrahedra that share corners with six equivalent EuAs6 octahedra, corners with six equivalent MnAs4 tetrahedra, edges with three equivalent EuAs6 octahedra, and edges with three equivalent MnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–50°. There are one shorter (2.42 Å) and three longer (2.45 Å) Mn–As bond lengths. As3- is bonded in a 7-coordinate geometry to three equivalent Eu2+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(MnAs)2 by Materials Project

SrMn2As2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent As3- atoms to form SrAs6 octahedra that share corners with twelve equivalent MnAs4 tetrahedra, edges with six equivalent SrAs6 octahedra, and edges with six equivalent MnAs4 tetrahedra. All Sr–As bond lengths are 3.14 Å. Mn2+ is bonded to four equivalent As3- atoms to form MnAs4 tetrahedra that share corners with six equivalent SrAs6 octahedra, corners with six equivalent MnAs4 tetrahedra, edges with three equivalent SrAs6 octahedra, and edges with three equivalent MnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 23–49°. There are one shorter (2.43 Å) and three longer (2.48 Å) Mn–As bond lengths. As3- is bonded in a 7-coordinate geometry to three equivalent Sr2+ and four equivalent Mn2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(MnAs)2 by Materials Project

CaMn2As2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent As3- atoms to form CaAs6 octahedra that share corners with twelve equivalent MnAs4 tetrahedra, edges with six equivalent CaAs6 octahedra, and edges with six equivalent MnAs4 tetrahedra. All Ca–As bond lengths are 2.99 Å. Mn2+ is bonded to four equivalent As3- atoms to form MnAs4 tetrahedra that share corners with six equivalent CaAs6 octahedra, corners with six equivalent MnAs4 tetrahedra, edges with three equivalent CaAs6 octahedra, and edges with three equivalent MnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–51°. There are one shorter (2.41 Å) and three longer (2.44 Å) Mn–As bond lengths. As3- is bonded to three equivalent Ca2+ and four equivalent Mn2+ atoms to form a mixture of distorted corner and edge-sharing AsCa3Mn4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Yb(MnAs)2 by Materials Project

YbMn2As2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Yb2+ is bonded to six equivalent As3- atoms to form YbAs6 octahedra that share corners with twelve equivalent MnAs4 tetrahedra, edges with six equivalent YbAs6 octahedra, and edges with six equivalent MnAs4 tetrahedra. All Yb–As bond lengths are 2.96 Å. Mn2+ is bonded to four equivalent As3- atoms to form MnAs4 tetrahedra that share corners with six equivalent YbAs6 octahedra, corners with six equivalent MnAs4 tetrahedra, edges with three equivalent YbAs6 octahedra, and edges with three equivalent MnAs4 tetrahedra. The corner-sharing octahedra tilt angles range from 20–51°. There are one shorter (2.41 Å) and three longer (2.44 Å) Mn–As bond lengths. As3- is bonded to three equivalent Yb2+ and four equivalent Mn2+ atoms to form a mixture of distorted edge and corner-sharing AsYb3Mn4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗