Crystal structures and magnetization distributions in the field dependent ferromagnetic shape memory alloy Ni54Fe19Ga27

P. J. Brown, A. P. Gandy, K. Ishida, Ryosuke Kainuma, T. Kanomata, Haruhiko Morito, K. U. Neumann, Katsunari Oikawa, K. R.A. Ziebeck

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18 Citations (Scopus)

Abstract

The mesoscopic and microscopic mechanisms giving rise to shape memory behaviour in single crystals of the ferromagnetic alloy Ni54Fe 19Ga27 have been investigated using polarized and unpolarized neutron diffraction. The measurements confirm that the Curie temperature TC coincides with the martensitic phase transition at TM ≤ 296K. At room temperature the crystal, as grown, had the tetragonal L10 structure with c/a≈1.20. It transformed to the cubic Heusler L21 structure at ≈330K. In subsequent heating and cooling cycles the transition took place at TM≈295K and it was found that applying a magnetic field raised TM by ≈0.3KT -1, making the material attractive for applications. The tetragonal structure has space group I4/mmm and is related to the cubic parent phase by a Bain transformation. The change in cell volume at the transition is only ≈1%, suggesting that the atomic moments are unchanged, although the magnetization drops significantly. The polarized neutron results show that in the cubic phase the magnetic electrons at the iron-rich sites have predominantly eg symmetry (60(3)%), a distribution similar to that observed in Fe3Al and Fe3Si. A small transfer of magnetization from Fe to Ni is associated with the martensitic transition, but no significant redistribution of magnetic electrons between orbitals whose degeneracy is lifted, such as that predicated by the band Jahn-Teller mechanism, was observed.

Original languageEnglish
Article number016201
JournalJournal of Physics Condensed Matter
Volume19
Issue number1
DOIs
Publication statusPublished - 2007 Jan 10

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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