Alloys spring to mind
Combinatorial array of alloys |
A wide range of other Ni-Mn-Ga alloys that exhibit "shape memory" but also magnetic properties have been found by Japanese scientists using a combinatorial approach.
Alloys that 'remember' their original shape after being deformed and revert to it on heating are widely used in many diverse applications from spectacle frames to instruments for keyhole surgery. Ni2MnGa is a ferromagnetic shape-memory alloy in which a magnetic field can be used to induce mechanical actuation. Now, Ichiro Takeuchi and colleagues at the University of Maryland have deposited a range of Ni-Mn-Ga alloys with different compositions simultaneously (so-called 'composition spreads') on to silicon substrates. They then used two novel characterization techniques to rapidly map the magnetic and shape-memory properties of the Ni-Mn-Ga composition spreads.
Ichiro Takeuchi |
First, they used a recently developed scanning room-temperature SQUID (superconducting quantum interference device) microscope to measure the magnetic field at the surface of each 2 x 2 mm sample in an array of different compositions. Secondly, the researchers determined the temperature at which the shape-memory-related phase transition occurs for each composition.
By exploiting these rapid screening techniques, the researchers could recreate the majority of the Ni-Mn-Ga phase diagram. "Ideal ferromagnetic shape memory alloys would have high magnetization and high phase transition temperatures," Takeuchi told Reactive Reports. Surprisingly, the team found that there is a pronounced trade-off between the two properties across the entire phase diagram - the higher the magnetization, the lower the transition temperature. The alloys with strongest magnetization occurred close to Ni-Mn-Ga composition and alloys with the highest transition temperatures occurred near Ga deficient, Mn rich compositions.
Takeuchi believes the research opens the door on materials with other combinations of useful properties, such as ferromagnetism, ferroelectricity, and shape memory effect.
Nature Materials, 2, 190 (2003); http://dx.doi.org/10.1038/nmat829
