Currently applied adaptive materials like piezoceramics or magnetostrictive materials can change their shape by applying an external electric or magnetic field and reach relative length changes of 0.1…0.2 %.
Especially piezoceramic functional materials had been a key requirement for several innovations. Applications range from the scanning tunnelling microscope to novel injection valves.
Another class of adaptive materials are the shape memory alloys, which can exhibit a reversible shape change due to temperature variation. The origin of this effect is the phase transformation between the high temperature "austenite" and the low temperature "martensite" phase.
In single crystals of special magnetic shape memory materials in 1996 a further, fundamentally new actuation mechanism
had been discovered in the martensite phase. It was observed, that already comparably low magnetic fields (< 1 Tesla) can be sufficient to move twin boundaries contained in the material. Since the twin boundaries are separating areas of different crystallographic orientations, their displacement leads to a reorientation of the crystal. This allows controlling the microstructure and shape of the sample
by applying magnetic fields. The observed change in length of up to 10 % is, compared to magnetostrictive or piezoceramic materials, by more than two orders of magnitude higher.
Due to the unique combination of very large strain, high energy density and relatively high actuation frequencies magnetic shape memory alloys thus allow novel applications which are not possible with conventional adaptive materials.
Within the area A of the SPP 1239 running since September 2006, the fundamentals of this material class are examined. Models are developed which describe the coupling of microstructure and magnetism from the atomistic dimensions to the device scale. Additionally, novel magnetic shape memory alloys are prepared and examined which promise better properties compared to today's materials.
Within area B, new and efficient preparation routes for bulk materials are developed. These materials are integrated into novel actuator and damping systems. An additional focus is on the characterisation of these materials with high lateral and temporal resolution.
Area C develops thin films with appropriate microstructure and texture. It is the aim to use the high miniaturization potential of the magnetic shape memory effect and to develop novel micro actuator and sensor systems.