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MA: Fachverband Magnetismus

MA 46: Poster II

MA 46.49: Poster

Thursday, March 21, 2024, 15:00–18:00, Poster C

Size effect of the first-order magnetostructural transition in Ni-Mn-Sn — •Johannes Puy1, David Koch1, Enrico Bruder1, Heiner Gutte2, Volodymyr Baran3, Konrad Opelt1,4, Franziska Scheibel1, and Oliver Gutfleisch11TU Darmstadt, Darmstadt, Germany — 2TU Bergakademie Freiberg, Freiberg, Germany — 3DESY P02.1, Hamburg, Germany — 4Fraunhofer IWKS, Hanau, Germany

Ni-Mn-Sn Heusler alloys exhibit a first-order magnetostructural transition (FOMST) and a large magnetocaloric effect. The FOMST is driven by a nucleation and growth mechanism. A size dependence of the FOMST can be observed in powder. However, conventional milling induces defects despite annealing, so the defect and size dependencies are difficult to disentangle. In this study, spherical, gas-atomized, and homogenized Ni-Mn-Sn powders with different size fractions are used to investigate the size dependence of the FOMST. Magnetic, structural, and microstructural analyses show a decrease in transition width and an increase in thermal hysteresis with decreasing particle size. Temperature-dependent magnetometry on single particles shows a sharp, jump-like FOMST for particles below 50 µm, while a continuous FOMST is observed for particles above 50 µm. Temperature-dependent X-ray diffraction shows a complete FOMST for all size fractions. Electron backscatter diffraction shows an average grain size of 20 µm for all particles. Therefore, the size dependence of FOMST can be correlated with the single- and polycrystalline nature of the particles. We thank the CRC/TRR 270 "HoMMage" for funding.

Keywords: martensitic transformation; size-dependence; gas-atomized powder; microstructure; grain boundaries

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