Characterization of a magnetic shape memory actuating element manufactured by laser ablation

Laser ablation (LA) was used to cut an actuating element from a single crystal of a magnetic shape memory alloy Ni50Mn28Ga22. A thorough characterization of the structural, magnetic, and mechanical properties of the LA-cut sample was performed. The LA cutting stabilized a fine twin structure with type 1 twins in the five-layered modulated martensitic phase of the alloy at ambient temperature. The sample exhibited a magnetic-field-induced strain of 4.5 %, and a 1.02 MPa twinning stress which is 7 % more when compared to an untreated crystal with polysynthetic fine twins. The observed increase of the twinning stress and a moderate increase of the stress-strain loop slope point to surface defects originating from the LA cutting, which act as pinning points for twin boundaries. Due to the stabilized fine twin structure, the sample demonstrated superior properties in high-rate magnetic actuation, reaching an actuation velocity of more than 4 m/s.