Papers by Keyword: Magnetic Shape Memory Effect (MSME)

Abstract: This study selects a single crystalline Ni-Mn-Ga alloy by its exceptional actuator attributes, high actuation speed, precise position control, rapid response to external magnetic fields, and extended operational lifespan. Researchers venture into uncharted territory, aiming to harness the potential of Ni-Mn-Ga alloy to revolutionize micropump performance and refine fluid manipulation within miniature devices. The methodology at the heart of this endeavor involves the seamless integration of this specialized alloy with microdevice technology, giving rise to a set of unique pump components that substantially boost pump efficiency. Crucially, Ni-Mn-Ga is the chosen material for the active part of the micropump. At the same time, MEMS fabrication handles the passive elements, all facilitated by the 0.18 µm semiconductor technology and Sivalco TCAD simulation software. Computational simulations validate the alloy's suitability, impressively achieving an accumulated flow volume of 0.15 x 10e-4 µL in 10 microseconds. Beyond its scientific significance, this research bridges MEMS technology and magnetic-enabled smart materials, showcasing the remarkable capabilities of Ni-Mn-Ga alloy in significantly enhancing micropump performance. These innovative solutions promise to open doors to groundbreaking applications in microfluidic systems across many scientific and industrial domains.

Abstract: The shape memory effect (SME) and magnetic shape memory effect (MSME) Fe-Pd thin film are using the film curvature method. The corresponding residual stress change due to theSME and MSME in Fe-Pd film is measuredduring thermal cycling and magnetic field changing. AFe-Pd thin film with a lateral composition gradient is deposited onto micromachined x7 cantilever beam arraysubstrate,such that each of the cantilever beams is coated with a film of different composition.There is abrupt stress change in only .1 at % Pd as the temperature of the film is cycled, and the corresponding stress change was measured as 0.16 GPa. The film with .4 at % Pd showsthe abrupt stress change at 0.7 Tesla, which means that the composition has the MSME.

Abstract: The role of magnetoelastic coupling in the mechanism of magnetically induced reorientation or redistribution (MIR) of twin variants is still a matter of some controversy. To evaluate this role ordinary magnetostriction of different Ni-Mn-Ga single crystals transforming to 5M (exhibiting MIR) and NM (no MIR) martensite were measured. The magnetostriction of Ni-Mn-Ga austenite is relatively low and steeply increases when approaching to martensite transformation. This is correlated to the softening of elastic modulus. Observed high field contribution of opposite sign may be due to the dependence of higher order elastic constant on magnetic field. The magnetostriction of martensite is difficult to determine as it is masked by much stronger MIR effect and indirect method must be used. The results are discussed in the frame of magnetoelastic model for MIR and compared with magnetic energy model.

Abstract: Ferromagnetic Heusler alloys like Ni-Mn-Z (Z = Al, Ga, In, Sn, Sb), which undergo a martensitic phase transformation, are on the edge of being used in technological applications involving actuator and magnetocaloric devices. The other class of ferromagnetic full Heusler alloys like Co-Mn-Z (Z = Al, Si, Ga, Ge, Sn) not undergoing a structural phase transition, are half-metals (in contrast to the Ni-based systems) with high spin polarization at the Fermi level and are of potential importance for future spintronics devices. On the basis of recent ab initio calculations, we highlight the main differences between the two classes of Heusler based materials.

Abstract: This article reports on two models for the shape memory effect and explains, how they are implemented in a finite element method program. The first model uses a phenomenological approach. For the example of a microgripper, the performance prediction of real actuators made of polycrystalline materials is demonstrated. In the second model, the martensite-austenite phase transition is treated as a thermodynamically activated process. Thermodynamic laws, like e.g. the minimization of the Gibbs free energy, are used for the formulation. To simplify the model, it is primarily intended to describe the behavior of single crystals. By comparing the simulated bending characteristic of a cantilever beam with experimental data, the applicability to polycrystalline material is tested. Due to the physics based formulation, this model gives more insight into the structural processes involved. This is very useful, e.g., for physical extensions needed for the simulation of the magnetic shape memory effect. It is shown, how the model can be extended to predict the behavior of actuators made of ferromagnetic Ni-Mn-Ga single crystals in a magnetic field.

Abstract: Transmission electron microscopy studies of the Ni2MnGa alloy showed that in the diffraction patterns there exist two additional effect apart from the spots given by the parent L21 Heusler phase and the tetragonal no modulate martensite. The first effect was the presence of sharp extra spots, lying on a direction significantly deviated from the <110>* for [001]β zone axis. These spots are connected with modulation of the parent phase. The value of the deviation angle is about 11-12°. The detailed analysis showed that the direction of the propagation vector of modulation is <641> type direction. The second effect visible in the [001]β diffraction patterns is the presence of the arcs located between the 220 type parent phase spots.. The analysis of this objects suggests that some chemical modulation exists with the period of <550>β. In this case short range ordering plays the essential role.

Abstract: In this paper the authors present a new one-dimensional phenomenological model of the magnetic shape memory effect (MSME) observed in magnetic shape memory alloys (MSMAs). The model takes into account elementary processes associated with the magnetisation of MSMAs. Its correctness has been checked against selected models known from the literature. The model developed by the authors has been verified in the case of a rod element made out of a MSMA by the use of the finite element method (FEM). A study on the influence of activation of MSMA beam actuators in the case of forced vibration of a composite beam has been performed. The authors have also carried out investigation connected with the influence of a transverse and open crack on the effectiveness of vibration reduction in the case of a composite beam by the use of MSM actuators.