The commercial use of magnetic shape memory alloys in actuating devices demands high mobility of the twin boundaries in combination with high operational temperatures. For applications in automotive engines, industry requires temperatures of at least 140°C. Thus this project aims to expand the operational temperature range whilst enhancing the crystal’s lifetime based on focused alloy design and sample preparation as well as crystallographic and mechanical characterizations. To cope with the insufficiency of the Bridgman technique for single crystal growth, the SLARE method, recently developed at HMI by A. Mecklenburg, was used for reliable and repeatable preparation of homogeneous single crystalline samples of known composition and low porosity.

Neutron diffraction experiments at BENSC (HMI, Berlin) of Ni_49.65Mn_29.28Ga_21.07 revealed a modulated martensitic structure stable up to 65°C (Curie-point at approx. 105°C). Based on the above mentioned composition substituting Ni by Co (Ni_46,65Co_6,14Mn_30.9Ga_19.05) yields a martensite-austenite transition temperature of above 120°C (Curie-point at approx. 157°C). Here the crystallographic and mechanical characterization of both alloys will be presented and discussed.

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