Microfabricated ferromagnetic-shape-memory Heuslers: The geometry and size effects

Ferromagnetic-shape-memory (FSM) Heuslers are a class of smart materials, promising for integration into miniaturized thermo/magnetomechanical devices, applicable in automotive, aerospace, biology, and robotics fields. In addition to compactness and mechanical simplicity, it is crucial for the material to maintain its properties at micro and nanometer scales. This study evidences the effects of lateral dimension and geometry on the properties of FSM Heuslers in patterned epitaxially grown Ni-Mn-Ga films. In particular, arrays of microstructures with lateral sizes down to the micrometer range, having different shapes and orientations with respect to the substrate edges, are investigated. The key properties of the material are stable after the microfabrication process: the martensitic transition temperatures increase by less than 3 K and thermal hysteresis changes by only 2 K. Notably, the size and geometry (i.e. shapeand orientation) of the patterned microstructures are reported to be a suitable tool for controlling the martensitic configuration. The study demonstrates selective response of a specific type of martensitic twin boundaries, i.e., X-type twin boundaries along [110] MgO and [1-10] MgO, to the shape and orientation of the microstructures showing a twin boundary selection of up to ~96%. The effects of lateral size, shape, and orientation on the martensitic and magnetic properties of the lithographically patterned structures are discussed