Influence of nanoscale order-disorder transitions on the magnetic properties of Heusler compounds for spintronics

J. Karel, J. E. Fischer, Simone Fabbrici, E. Pippel, P. Werner, M. Vinicius Castergnaro, P. Adler, S. Ouardi, B. Balke, G. H. Fecher, J. Morais, F. Albertini, S. S. P. Parkin, C. Felser

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Abstract

Modifications in nanoscale chemical order are used to tune the magnetic properties, namely TC, of Co2FeSixAl1-x (0 < x < 1). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with Z-contrast reveals nanoscale regions of L21 order within a B2 matrix in the off-stoichiometry samples. Perhaps surprisingly, the latter, more chemically disordered structure, exhibits a higher TC. Upon annealing, the off-stoichiometry samples become more homogeneous with the fraction of L21 order decreasing. The short-range order was also investigated using X-ray absorption fine structure (XAFS) measurements at the Co and Fe K edges. Since the local atomic environments of Co atoms in the L21 and B2 structures are identical, the features presented in the Co K edge XAFS data are the same in both cases. By contrast, the L21 and B2 structures exhibit different signatures at the Fe K edge owing to the different chemical environments. Fitting of these spectra confirms the nanoscale chemical disorder observed by HAADF-STEM and the expected role this disorder plays on TC. Our results point to a methodology that might be extended to modify the magnetic and electronic properties of any Heusler compound; chemical disorder can be an engineering tool to realize highly tailored properties.

Original languageEnglish
Pages (from-to)4388-4392
Number of pages5
JournalJournal of Materials Chemistry C
Volume5
Issue number18
DOIs
Publication statusPublished - 2017

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