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Long‐ and short‐range order in the Ni 52 Co 2 Fe 20 Ga 26 ferromagnetic Heusler alloy
Author(s) -
Macovei Dan,
Tolea Felicia
Publication year - 2021
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576721006415
Subject(s) - materials science , austenite , extended x ray absorption fine structure , alloy , martensite , tetragonal crystal system , crystallography , atmospheric temperature range , ferromagnetism , phase (matter) , condensed matter physics , metallurgy , crystal structure , microstructure , absorption spectroscopy , thermodynamics , chemistry , optics , physics , organic chemistry
The crystalline structure and Fe local environment in a Co‐doped Ni–Fe–Ga Heusler alloy, prepared by the melt‐spinning technique, were investigated by X‐ray diffraction (XRD) and EXAFS at room and low temperatures. The characteristic temperatures of the austenite–martensite phase transitions were determined by differential scanning calorimetry via cooling and heating cycles of the alloy ribbons. As shown by room‐temperature XRD, the austenitic phase of the alloy has the chemically ordered L2 1 Heusler structure. This was confirmed by EXAFS, although this technique was not able to conclusively distinguish between the L2 1 and B2 structures of the austenite for the analyzed alloy. The low‐temperature martensitic phase and its structural evolution towards austenite with increasing temperature were studied by high‐energy X‐ray diffraction, which evinced the martensite modulation. However, the Fe environment could be fitted by EXAFS with the tetragonal L1 0 structure of the non‐modulated martensite. This proves that the martensite modulation has structural effects on a long‐range scale, without significant changes in the short‐range order around the atoms. The changes in the local structure around iron on martensitic transformation were correlated with changes in the electronic structure, described by XANES spectroscopy at the Fe K edge.