Observation of reverse transformation in metamagnetic shape memory alloy Ni₄₀Co₁₀Mn₃₄Al₁₆by high-field X-ray diffraction measurements

The structural properties of metamagnetic shape memory alloy Ni ₄₀Co₁₀Mn₃₄Al₁₆ were investigated by X-ray powder diffraction measurements in the temperature range from 283 to 473 K and magnetic fields up to 5 T. With increasing temperature from 283 K, the alloy undergoes the reverse martensitic transformation from the tetragonal Ll₀-type structure with the lattice parameter a_t = 0.3853 nm and c_t = 0.3299 nm into the B2-type cubic structure with the lattice parameter a_c = 0.2924 nm at A_s = 383 K. At 408 K (>A_s), we directly observed the field-induced reverse martensitic transformation.