Magnetic Shape Memory Turns to Nano: Microstructure Controlled Actuation of Free‐Standing Nanodisks. Issue 49 (7th October 2018) - Campanini, Marco
Abstract: Magnetic shape memory materials hold a great promise for next‐generation actuation devices and systems for energy conversion, thanks to the intimate coupling between structure and magnetism in their martensitic phase. Here novel magnetic shape memory free‐standing nanodisks are proposed, proving that the lack of the substrate constrains enables the exploitation of new microstructure‐controlled actuation mechanisms by the combined application of different stimuli–i.e., temperature and magnetic field. The results show that a reversible areal strain (up to 5.5%) can be achieved and tuned in intensity and sign (i.e., areal contraction or expansion) by the application of a magnetic field. The mechanisms at the basis of the actuation are investigated by experiments performed at different length scales and directly visualized by several electron microscopy techniques, including electron holography, showing that thermo/magnetomechanical properties can be optimized by engineering the martensitic microstructure through epitaxial growth and lateral confinement. These findings represent a step forward toward the development of a new class of temperature‐field controlled nanoactuators and smart nanomaterials. Abstract : A new actuation mechanism is demonstrated for free‐standing Ni2 MnGa nanodisks, with a reversible areal strain tunable in intensity and sign by the application of a magnetic field. The actuation mechanisms are correlated to magnetostructural transformations and visualized by various electron microscopy techniques. The magnetothermal properties of NiMnGa nanodisks pave the way for a new class of temperature‐field controlled nanoactuators.