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Title: Direct observation of a band Jahn–Teller effect in the martensitic phase transition of Ni2MnGa
Authors: Brown, P.J.
Bargawi, A.Y.
Crangle, J.
Neumann, K-U.
Ziebeck, K.R.A.
Issue Date: 1999
Publisher: © Institute of Physics
Citation: BROWN et al, 1999. Direct observation of a band Jahn–Teller effect in the martensitic phase transition of Ni2MnGa. Journal of Physics: Condensed Matter, 11(24), pp. 4715-4722
Abstract: Polarized neutron scattering has been used to determine the changes in the distribution of unpaired electrons which take place in the martensitic transition in Ni2MnGa. Ni2MnGa is a ferromagnetic Heusler alloy which undergoes a reversible transition at about 220 K from a high temperature cubic phase to a low temperature tetragonal one. It has been suggested, on the basis of band structure calculations, that the structural phase transition is driven by a band Jahn–Teller distortion involving redistribution of electrons between 3d sub-bands of different symmetries. The results of the neutron scattering experiments showthat the transition from the cubic to the tetragonal phase is accompanied by a transfer of magnetic moment from Mn to Ni. The unpaired electrons in the cubic phase have overall eg symmetry. In the tetragonal phase, the degeneracy of the eg and t2g bands is raised and the unpaired electrons are redistributed in such a way that the subbands based on orbitals extending towards the c-axis are preferentially occupied. Although the experimental moments differ in detail from those expected from band structure calculations, the change in symmetry of the magnetization distribution is consistent with a band Jahn–Teller origin for the phase transition.
Description: This article was published in the journal, Journal of Physics: Condensed Matter [© Institute of Physics]. It is available at: http://www.iop.org/EJ/journal/JPhysCM.
URI: https://dspace.lboro.ac.uk/2134/1708
ISSN: 0953-8984
Appears in Collections:Closed Access (Physics)

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