Abstract
Heusler alloys of Ni-Mn-Ga compositions demonstrate ferromagnetic shape memory effect in the martensitic state. The transformation temperature and the chemical order depend strongly on the composition. In the current work, the structure and chemical order of the martensitic phase of Ni1.91Mn1.29Ga0.8 were studied using neutron diffraction; the diffraction pattern was refined using the FullProf software. It was determined that the structural transition occurs around 330K. At room temperature, 300K, which is below the martensite transformation temperature, all the Bragg reflections can be described by a monoclinic lattice with a symmetry of space group P 1 2/m 1 and lattice constants of a = 4.23047(7) [Å], b = 5.58333(6) [Å], c = 21.0179(2) [Å], beta = 90.328(1). The chemical order is of critical importance in these alloys, and it was previously studied at 363K. Analysis of the neutron diffraction in the monoclinic phase shows that the chemical order is maintained during the martensitic transformation.
| Original language | English |
|---|---|
| Pages (from-to) | S853-S857 |
| Journal | Materials Today: Proceedings |
| Volume | 2 |
| DOIs | |
| State | Published - 2015 |
Funding
The authors are grateful for their technical discussions with Drs. A. Sozinov and G. Kimmel. This work was supported by Award No. RUP1-7028-MO-11 of the US Civilian Research & Development Foundation (CRDF) and by the National Science Foundation under Cooperative Agreement No. OISE-9531011. The authors also wish to acknowledge the US National Science Foundation award number NSF-0831951, and the support of the Academy of Finland (grant no. 259235). Research at Oak Ridge National Laboratory was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences and the US Department of Energy.
Keywords
- Chemical Order
- Magnetic Shape Memory
- Neutron Diffraction
- Ni-Mn-Ga alloy
- Rietveld Method
- Structure Refinement