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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FUNMAH (Novel Functionality of Magnetic Shape Memory Alloys by Magnetic Hysteresis Control)

Teaser

Summary

\"In the project we investigate magnetic shape memory (MSM) alloys, which are smart materials exhibiting large shape changes in magnetic field and related wide range of magnetomechanical functionalities. They are promising for applications such as fast magnetic actuators, low power magnetic actuators, magnetic sensors, energy harvesters, medical micropumps, or magneto-structural memory.

It was proposed by the fellow that novel functionalities of MSM alloys can be obtained when magnetic coercivity of the material is enlarged. Such novel functionalities are for example mechanically-induced demagnetization and remanent magnetization rotation. MSM material with enlarged magnetic coercivity behaves as a kind of smart semi-permanent magnet, since it its magnetization can be rotated or \"\"turned off\"\" by mechanical stress. This is interesting scientifically but also for applications.

The objective of this project was to build comprehensive understanding of the magnetic coercivity and novel functionalities of Ni-Mn-Ga(-B) MSMAs. Particular topics were i) what is the physical mechanism of magnetic coercivity enlargement in prototype Ni-Mn-Ga(-B) magnetic shape memory alloy, ii) what is the physical mechanism underlying the functionalities, and iii) illustration of the functionality in applications.

The most of the project objectives was achieved. Most importantly, we were able to reveal the physical mechanisms behind the magnetic coercivity and we showed the way in which the magnetic coercivity can be controlled and thus the novel functionality enabled in Ni-Mn-Ga based MSM alloys.\"

Work performed

\"The understanding of magnetic coercivity is critical for understanding and enabling of the novel functionality in MSM alloys. One way how to control coercitivity is material doping. We studied the magnetic properties of Co, Cu, and B doped Ni-Mn-Ga materials but we did not find any effect of doping on the magnetic properties. Then we focused on the hypothesis that the coercivity is caused by so-called antiphase boundaries. These are boundaries on which structure order is changed. We developed a new method of visualization of antiphase boundaries by magnetic force microscopy. With a great help of this method we were able to detect the density of antiphase boundaries for various thermal treatment of the material. In the end we were able to achieve increased hysteresis by a thermal treatment. Importantly, in contrast by other methods, e.g. by introducing precipitates, we were able to maintain the ability of material to reorient in magnetic field. Thus we showed the way, how the novel functionality can be enabled.

For physical mechanisms underlying the novel functionalities, the understanding of the twinned microstructure of MSM alloys is critical. We studied the twinned microstructure of the material and made important findings. First of all we found a new type of twinning, so-called non-conventional twins, and also we identified the changes in microstructure during bending of the material. We also found nanotwinning in the material, which was not previously reported. All these findings are important for the reorientation in magnetic field and related both for the ordinary as well as for the novel functionality.

Related to application usage of the MSM materials we focused on the microscale applications since this is region where the novel functionalities are most likely to be used. We studied the possibilities of focused Xe-ion beam milling for preparation of MSM microdevices. We were able to create micropillars and developed a method of treatment of their surface, which resulted in functional micropillars. The micropillars were studied further and in the end we were able to demonstrate ultrafast actuation with micropillars.

All the above results were described in detail in international scientific publications. Results were also disseminated on the project webpage www.funmah.eu, on the scientific conferences (ISPMA 15, Actuator 2018 and Esomat 18) and seminars and workshops (e.g. Ostre 2018). In addition the results on microdevices were displayed on the popular \"\"week of science\"\" events and we prepared one popular article on the MSM alloys, which is now under consideration for publication.\"

Final results

There are several distinct findings of the project which define new state of art.

- We developed original method to visualize the antiphase boundaries by magnetic force microscopy. Antiphase boundaries were identified to be the key for the control of coercivity and novel functionality.

- The mechanisms and reasons of enlarged magnetic coercivity in Ni-Mn-Ga were explained and it was shown that only the thermal treatment is essential, not the doping of material by B.

- We discovered nanotwinning and non-conventional twinning in magnetic shape memory alloy.

- We as first experimentally demonstrated the capability of material to actuate rapidly on microscale.

The project results extend the scientific understanding of magnetic shape memory alloys and broaden their application potential. The results may be beneficial for future MSM technology use. Although the project was basic research oriented the results are relevant to potential applications of the magnetic shape memory alloys. In addition to the basic material science knowledge obtained, the society and general public will benefit from the results of the project in the future applications foreseeing the magnetic shape memory technology in medicine, airspace and automotive, robotics or energy technology.