Magnetic Shape Memory Microactuators

Abstract

By introducing smart materials in micro systems technologies, novel smart microactuators and sensors are currently being developed, e.g., for mobile, wearable, and implantable MEMS (Micro-electro-mechanical-system) devices. Magnetic shape memory alloys (MSMAs) are a promising material system as they show multiple coupling effects as well as large, abrupt changes in their physical properties, e.g., of strain and magnetization, due to a first order phase transformation. For the development of MSMA microactuators, considerable efforts are undertaken to fabricate MSMA foils and films showing similar and just as strong effects compared to their bulk counterparts. Novel MEMS-compatible technologies are being developed to enable their micromachining and integration. This review gives an overview of material properties, engineering issues and fabrication technologies. Selected demonstrators are presented illustrating the wide application potential.

Study of 10M' Nanotwinned Phase in the Vicinity of Martensitic Transformation in Ni-Mn-Ga Magnetic Shape Memory Alloy

“…The discovery of magnetic shape memory (MSM) effect by Ullakko et al in 1996 [1] started a development of MSM alloys with exceptional properties for applications as sensors and actuators [2][3][4]. The archetypal and probably most studied MSM alloy is the Ni-Mn-Ga. Martensite of Ni-Mn-Ga exhibits giant magnetic field-induced strain (up to 12% [5]) in a moderate magnetic field (<1 T).…”

“…The twinned microstructure of MSM alloys originates from the martensitic transformation from the cubic austenite phase to lower symmetry martensite. We focus on the non-stoichiometric compositions of the Ni-Mn-Ga resulting in five-layered modulated monoclinic martensite structure (10M), which is the most promising structure for applications [3,4].…”

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

“…[6,13,14] In this context, thin films display a great potential with respect to bulk materials for their possible integration in micro/ nanosystems for the fabrication of new-concept devices such as actuators, valves, energy harvesters, and solid-state microrefrigerators. [15,16] Nonetheless, the intimate link between magnetic and structural degrees of freedom and the peculiar hierarchical twin-within-twin martensitic structure makes epitaxial films a unique platform for the precise control of structure and magnetism from the atomic to the macroscale.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.…”

Modelling Shape-Memory Effects in Ferromagnetic Alloys

“…It consists of the possibility of recovering, upon loading and unloading, a large strain (in some cases C10 %) associated with the stress-or strain-induced transformation. Indeed, these properties make this class of materials very attractive from a technological point of view, since they may function as sensors as well as actuators, and are promising candidates for smart materials [8,9].…”