Dresden 2014 – scientific programme

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MA: Fachverband Magnetismus

MA 38: Magnetic Materials II

MA 38.6: Talk

Thursday, April 3, 2014, 11:00–11:15, HSZ 403

Martensitic Transformation in Freestanding Magnetocaloric Thin Films — •Lars Helmich¹, Niclas Teichert¹, Walid Hetaba², Anna Behler³, Anja Waske³, and Andreas Hütten¹ — ¹Bielefeld University, Department of Physics, Thin Films and Physics of Nanostructures, 33615 Bielefeld, Germany — ²Vienna University of Technology, USTEM, A-1040 Vienna, Austria — ³TU Dresden, Institut für Festkörperphysik, 01062 Dresden, Germany

Ni-Mn-Sn is a well-known ferromagnetic shape memory alloy that shows both a martensitic transformation and the magnetocaloric effect for a suitable choice of stoichiometry. However a direct observation of the temperature change due to the magnetocaloric effect is a challenging task for thin films since the substrate provides a large heat sink.

We prepared Ni-Mn-Sn films on heated MgO(001) substrates with a sacrificial layer in between by magnetron sputtering. In a subsequent preparation step the substrate was removed by wet-chemical treatment. Thus we prepared freestanding films with a thickness in the range of 100 nm and therefore we got rid of the heat sink. This offers the possibility for direct ΔT-measurements.

Moreover the removal of the substrate leads to a reduction of strain effects in the film. We showed that this again results in a lowering of the martensite transition temperature. Furthermore changes in electronic and magnetic properties were analysed.