Magnetic Shape Memory Turns to Nano: Microstructure Controlled Actuation of Free‐Standing Nanodisks

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.

Following the Martensitic Configuration Footprints in the Transition Route of Ni-Mn-Ga Magnetic Shape Memory Films: Insight into the Role of Twin Boundaries and Interfaces

“…It is worth mentioning that close to the substrate interface (~50 nm), we observed a pronounced branching of the twins with type I boundaries, which are shown in the supplementary material ( Figure S2). This represents an experimental evidence for the model proposed as the diamond model of the nucleation and growth of the martensitic nuclei in Y-type configuration [24]. Figure 3a shows the HAADF image of the lamella prepared from sample #2, alternating stripes with bright and dark contrasts, around 45 • and −45 • tilted with respect to the substrate, which are typical of X-type configuration.…”

“…Therefore, in order to find possible solutions to overcome these obstacles, it is necessary to gain a comprehensive view of the configuration of the twin variants at the different length scales and its evolution upon martensitic phase transition. In the literature, there are a few works focused on the crystallographic structures and the martensitic configurations of epitaxial Ni-Mn-Ga thin films through experiments and models [7][8][9][10][24][25][26]. However, the knowledge about the multiscale hierarchical self-accommodation of the twin variants in the martensitic phase and its possible links to the transition route is still limited, mainly due to lack of direct multiscale observation.…”

Self‐Patterning of Multifunctional Heusler Membranes by Dewetting

“…However, these chemically ordered Heusler alloys are a challenge for microtechnological processing. [12,[15][16][17] A particular problem is the damage caused by ion beam methods, because this damage needs to be removed afterward. [18] This processing could be minimized if the multifunctional material brought itself into the desired shape through self-patterning.…”

Au-Coated Ni80Fe20 Submicron Magnetic Nanodisks: Interactions With Tumor Cells

“…Au-coated Ni 80 Fe 20 nanodisks have been prepared by a combination of sputter deposition and self-assembling of polystyrene nanosphere lithography, following the procedure detailed elsewhere (Tiberto et al, 2015;Campanini et al, 2018). The high versatility of this procedure allows finely tuning the nanodisk thickness and diameter, which can be sized from the nano-to the submicron scale (Tiberto et al, 2015(Tiberto et al, , 2016Campanini et al, 2018). In this work, we set the diameter at 650 nm and the thickness at 30 nm to guarantee, in combination with the soft magnetic properties of NiFe alloy, the formation of a stable magnetic vortex domain configuration.…”