Regensburg 2016 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 24: Topical session: Caloric Effects in ferroic materials II - Methods and Applications
MM 24.5: Vortrag
Dienstag, 8. März 2016, 13:00–13:15, H53
Magnetocaloric properties of freestanding and substrate-constrained Ni-Mn-Ga-Co films — •Anett Diestel1,2, Robert Niemann1, Benjamin Schleicher1, Stefan Schwabe1,2, Ludwig Schultz1,2, and Sebastian Fähler1 — 1IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, D-01171 Dresden, Germany — 2TU Dresden, Institute of Materials Science, D-01062 Dresden, Germany
Ferroic cooling processes that rely on field-induced first-order transformations of solid materials are a promising step towards a more energy-efficient refrigeration technology. In particular thin films are discussed for their fast heat transfer and possible applications in microsystems. They can be used as model systems to understand the transformation mechanism. We analyze the martensitic transformation in substrate-constrained and freestanding epitaxial Ni-Mn-Ga-Co films. By means of M(T) and M(H) measurements in vicinity of the phase transformation, we compare entropy changes and field-temperature phase diagrams, which differ only slightly depending on the scanning parameter. These effects are related to the vector character of a magnetic field, which acts differently on the nucleation and growth processes compared to the scalar character of temperature. We observed an asymmetric thermal hysteresis between the ferromagnetic austenite and the ferromagnetic martensite. The sharp cooling but gradual heating branch at low magnetic fields is explained by using a microstructural model of martensitic transformation describing energy barriers of nucleation and growth processes. This work was funded by the DFG SPP1599.