Dresden 2017 – wissenschaftliches Programm
MA 11.2: Vortrag
Montag, 20. März 2017, 15:20–15:40, HSZ 101
On the magnetocaloric properties of Heusler compounds — •T. Gottschall, D. Benke, K.P. Skokov, M. Fries, I. Radulov, and O. Gutfleisch — TU Darmstadt, Institute of Material Science, Alarich-Weiss-Str. 16, 64287 Darmstadt, Germany
Large magnetocaloric effects can be obtained in the Heusler alloy systems Ni-Mn-In and Ni-Mn-In-Co during the magnetostructural phase transformation between the low temperature paramagnetic martensite and the high temperature ferromagnetic austenite phase. The martensitic transition takes place by a nucleation and growth process and can be tuned in a wide temperature window by varying the chemical composition. It is furthermore sensitive to a magnetic field but also to hydrostatic pressure. The phase transformation can therefore be induced by those external stimuli . However, the existence of thermal hysteresis is inevitable in those materials limiting the reversible adiabatic temperature ΔTad and isothermal entropy change ΔST.
The magnetocaloric effect under cycling can be enhanced when the material remains all the time in a mixed-phase state, in so-called minor loops of hysteresis . On the contrary, in very high magnetic-field rates as well as in micrometer-sized single particles, the thermal hysteresis increases significantly, which needs to be considered in terms of application . In order to understand the contrasting behavior of small fragments in comparison to their bulk representatives, a finite element model is introduced, from which the importance of mechanical stress during the first-order transition becomes apparent. Furthermore, an attempt is made to improve the sustainability of magnetocaloric Heusler alloys by the substitution of critical elements to move this interesting material class further towards application.
This work was supported by DFG (Grant No. SPP1599)
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