Regensburg 2025 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 7: INNOMAG e.V. Prizes 2025 (Diplom-/Master and Ph.D. Thesis)

MA 7.3: Hauptvortrag

Montag, 17. März 2025, 15:40–16:00, H18

Tailoring the first-order magnetostructural phase transition in Ni-Mn-Sn for caloric applications by microstructure — •Johannes Puy, Enrico Bruder, Oliver Gutfleisch, and Franziska Scheibel — TU Darmstadt, Darmstadt, Germany

Ni-Mn-Sn Heusler alloys show a large inverse magnetocaloric (MCE) and conventional elastocaloric effect (ECE), making them a promising candidate for multicaloric cooling. The caloric effects arise from a first-order magnetostructural phase transition (FOMST) from high-magnetic austenite to low-magnetic martensite, driven by a nucleation and growth process. Optimizing the multicaloric performance of these materials requires tailoring the FOMST, which implies a comprehensive understanding of the role of microstructure and coupling factors, such as atomic, magnetostatic, and stress coupling. In this study, the influence of microstructure and defects (grain boundaries, pores, sintering necks) on the temperature-driven FOMST is investigated in single- and polycrystalline particles, as well as in spark-plasma-sintered Ni-Mn-Sn. By adjusting the relative density, the effect of porosity on the FOMST is studied. Temperature-dependent magnetometry reveals that an increase of the relative density from 88 % to 99 % narrows the transition ranges from 18 K to 9 K and decreases the transition temperature from 263 K to 254 K. Temperature-dependent in-situ optical and in-situ scanning electron microscopy reveal preferential martensite nucleation at free particle surfaces in powder and sintered, 88% dense Ni-Mn-Sn, while nucleation in 99 % dense Ni-Mn-Sn is favored at sintering necks. We thank the CRC/TRR 270 'HoMMage' for funding.

Keywords: martensitic transformation; magnetocaloric; nucleation; microstructure; coupling