Using the Ginzburg-Landau theory, phenomenological phase diagrams of Heusler alloys Ni-Mn-Ga are theoretically investigated. We take into account the magnetic, elastic and micro-modulation order parameters in order to understand their coupling in the real system. We focus on the aspect of crystal modulation which appears at c/a<1 only, and is never observed for tetragonal distortions characterized by c/a>1. The influences of the parameters are discussed on the basis of phase diagrams. From different phase diagrams we choose those corresponding to the experimental situation and draw a conclusion that two opposite tetragonal distortions, c/a<1 and c/a>1, must be driven by different instabilities having different microscopic origins.
- Ferromagnetic shape memory alloys
- Modulation of the crystal lattice
- Structural and magnetic phase transitions
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics