Structure and microstructure of Ni-Mn-Ga single crystal exhibiting magnetic shape memory effect analysed by high resolution X-ray diffraction
Abstrakt
Subtle changes of (micro-) structure can have far-reaching consequences for magnetic shape memory (MSM) effect, also called magnetic induced reorientation (MIR). Detailed X-ray structure analysis using reciprocal mapping of Ni-Mn-Ga single crystals exhibiting MIR at room temperature and prepared in single macrotwin orientation revealed 10M modulated structure.
It indicated that the modulation was harmonic, i.e. commensurate, but it also showed that the difference when compared to non commensurate mode or even to adaptive model was very small. The distinction between commensurate and non-commensurate modulation could not be reliably resolved due to large broadening of diffraction peaks.
The broadening was caused by small size (less than 100 nm) of structurally coherent L2(1) ordered domains. The small size of these coherent domains is a result of large concentration of antiphase boundaries.