Structural Order, Martensitic Transformation and Magnetic Domains in Ni-Fe-Ga Shape Memory Microwire
Abstrakt
We investigate Ni50Fe27Ga23 prepared as glass-coated microwires by the Taylor-Ulitovsky method. Temperature-induced martensitic transformation was observed by cooling in liquid nitrogen using optical microscope.
From cubic austenite the wire transformed to heavily twinned martensitic phase. The magnetic domain structure (domain size and orientation) and its evolution were observed by magnetic force microscope at the same place after the sample was magnetized in three perpendicular directions.
Surprisingly, after various magnetizing the domain structure stayed similar, and changes were minor. This probably happened due to presence of antiphase boundaries on which the domain walls are pinned.
The Mossbauer spectroscopy determines the ratio between ten percent of Fe atoms in non-magnetic state and the magnetically ordered phase with L2(1) order which is typical for austenite.