Researchers from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, in collaboration with a research group from Beihang University, have developed a Ni₃₄Co₈Cu₈Mn₃₆Ga₁₄ single crystal that exhibits giant magneto-superelasticity of 5%. This means that the crystal can return to its original shape after being deformed, triggered by a magnetic field rather than physical stress.

The results were published in Advanced Science.

Elasticity is the ability of a material to return to its original shape after deformation. Most metals can do this up to a strain of about 0.2%. Some special alloys, such as shape memory alloys and high entropy alloys, can exhibit superelasticity, where they can withstand much larger strains and still return to their original shape. This is usually induced by the application of an external stress. However, magneto-superelasticity is induced by a magnetic field, opening up new possibilities for the design of contactless devices and efficient energy transducers.

In this study, the researchers performed stress-constrained transition cycling training on the Ni₃₄Co₈Cu₈Mn₃₆Ga₁₄ single crystal. They applied compressive stress, which introduced arrays of ordered dislocations - defects in the crystal structure that were oriented in a specific way. These dislocations played a critical role in forming specific martensitic variants, which are special arrangements of atoms that occur during a reversible transformation induced by a magnetic field.

Using phase field simulations, the researchers confirmed that the internal stress generated by these organized dislocations helped to shape these preferred martensitic variants. This combination of reversible martensitic transformation and preferential orientation enabled the single crystal to achieve a remarkable 5% magneto-superelasticity.

To demonstrate the potential of this material, they designed a device that uses a pulsed magnetic field. With a pulse duration of 10 milliseconds, the device achieved a significant stroke at room temperature, thanks to the crystal's giant magneto-superelasticity. It also demonstrated a fast response to an 8-millisecond pulse, with only a 0.1-millisecond delay.

"Our work provides an attractive strategy to access high-performance functional materials through defect engineering.," said Prof. WANG Jingmin of Beihang University.

Magneto-elasticity of the Ni₃₄Co₈Cu₈Mn₃₆Ga₁₄ single crystal. a1&b1. Schematic illustration of self-accommodated and preferentially oriented martensitic variants without and with ordered dislocations; a2&b2. The corresponding experimental results on the small and giant magnetoelastic strain, respectively. (Image by YU Qijia)