Magnetic domain structure in the presence of very thin martensite plates: Electron holography study on a thin-foil Fe-31.2 at.%Pd alloy

The magnetic domain structure of a thin-foil Fe-31.2 at.%Pd alloy, wherein the thickness of the martensite plates (of the order of 10 nm) is comparable to that of the magnetic domain walls, has been studied by electron holography and Lorentz microscopy. Magnetic flux maps obtained by electron holography demonstrate that the magnetization vectors are not necessarily oriented along the easy magnetization axis of the martensite - the result is in sharp contrast to the case of thick martensite plates (of the order of 10² nm or larger). This observation provides important information for actuator applications that utilize thin-foil ferromagnetic shape memory alloys. The change in the magnetic domain structure with the face-centered cubic to face-centered tetragonal martensitic transformation is also discussed.