Single phase boundary actuation of a ferromagnetic shape memory foil

Magnetic Shape Memory Microactuators

“…Based on theoretical considerations, the critical magnetic field for MIR is expected to decrease for decreasing foil thickness [10]. However, in real foil specimens, the critical magnetic field and maximum magnetostrain are affected by material inhomogeneity and surface defects depending on the technology of foil fabrication as well as by the constraints of fixation and tensile loading [34,45]. The influence of defects on the mobility of twin boundaries can be reduced by training of the MSMA material.…”

“…In this case, single phase boundary actuation results in the formation of a single variant martensite state similar to the case of MSM actuation. As illustrated in the inset of Figure 8a, the maximum strain response is given by the difference of the short c-axis of tetragonal martensite and the axis of cubic austenite to be 4.1% [34]. Similarly, the magnetic field may be applied in a perpendicular direction to the thermal field gradient resulting in a smaller strain change of −1.9% that is given by the difference of the long a-axis of tetragonal martensite and the axis of cubic austenite [34].…”

“…As a drawback, the overall complexity of the actuator device increases and miniaturization remains limited. Recently, it has been shown that thermal actuation by applying a temperature gradient could be an interesting alternative approach as it allows controlling the location of phase nucleation and the propagation of phase front [34].…”

“…The influence of defects on the mobility of twin boundaries can be reduced by training of the MSMA material. Different methods of thermo-magneto-mechanical training have been developed and their effect on magneto-strain and stress-strain characteristics have been investigated [9,34].…”

“…Actuation mechanism Reference Magnetic field-induced reorientation (MIR) of martensite Magnetic shape memory (MSM) actuation [4] Temperature gradient-induced martensitic transformation Single phase boundary actuation [34] Thermally induced ferromagnetic transition and martensitic transformation Bidirectional magnetostatic and thermoelastic actuation [35] Thermally induced metamagnetic transition Thermomagnetic actuation [36] Magnetic stray-field-induced microstructure Magnetic stray-field induced actuation [37] …”