University of Bialystok
under the auspices
of the Committee of Crystallography, Polish Academy of Sciences
This School is financially supported in part by
the International Union of Crystallography and the European Crystallographic Association
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
Topics
- The physics of shape memory materials is explored using the example of the ferromagnetic Heusler alloy Ni2MnGa. Ni2MnGa is unique in displaying a martensitic phase transition within a ferromagnetically ordered state and with characteristics which make this material very attractive for applications.
Length changes of Ni2MnGa samples of up to ~5% have been observed when this material undergoes the martensitic phase transition. Such huge changes are to be contrasted with the value of thermal expansion, which usually is of the order of 1% when a material is heated from T=0K to its melting temperature. While such large length changes are surprising it is even more astonishing to find that single crystals can (repeatedly!) undergo such large macroscopic changes in length without an apparent degradation of their structure at an atomic level.
Structural and magnetic properties are presented and reviewed. In particular the results of detailed neutron scattering experiments will be discussed. The mechanism of the martensitic phase transition, which is at the heart of the shape memory effect, is introduced with a microscopic model.
The properties of Ni2MnGa and Ni2+xMn1-xGa are contrasted with other Heusler alloys which also undergo a shape memory transformation.