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Crystallographic Boundary in a Magnetic Shape Memory Material Print
Wednesday, 18 April 2012 11:37

 

A research team has shown the existence of a special structural boundary in an intermetallic compound by combining the unique measurement facilities at the ALS, the single-crystal production capabilities of Tohoku University (Japan), and the materials science expertise of Johannes-Gutenberg-University (Germany). Conventional shape memory materials, such as the commercially available Nitinol (an alloy of nickel and titanium used in microsensing, actuation, and medical devices), undergo a phase transformation with cooling or heating when large areas of a sample distort along a single axis, and where the atomic-unit cell “stretching” from a cube to a rectangular prism occurs. In contrast, magnetic shape memory (MSM) materials are much more rare but have an advantage: The axis of magnetic anisotropy is coupled to the direction of stretching, so a perfect MSM crystal can be made to flex and bend reversibly by applying an external magnetic field.

The research team used the photoelectron emission spectromicroscope on ALS Beamline 11.0.1 to acquire nanoscale, element-specific images of a crystallographic boundary in Fe2MnGa, a new MSM compound. With heating and cooling, the boundaries between some magnetic domains are observed to sweep back and forth, while others are stationary because the local direction of stretching is incompatible with domain-wall motion. Knowledge of this kind of magnetostructural domain wall will be useful in tailoring the properties of MSM crystals for robotic and medical applications.

 

 

 

Two images are taken with opposite incident photon helicity at each of the characteristic absorption energies for manganese (Mn, left) and iron (Fe, right) at the surface of Fe2MnGa. There is zero (grey) contrast in the Mn image and strong (black/white) contrast for the Fe, indicating that the surface magnetization comes from the Fe. One mangetostructural domain boundary is observed to sweep through the bulk of the material while the other is pinned.

 



Work performed on ALS Beamline 11.0.1.

Citation: C.A. Jenkins et al. "Temperature-induced martensite in magnetic shape memory Fe2MnGa observed by photoemission electron microscopy," Appl. Phys. Lett. 100, 032401 (2012). Full Article (PDF)