Phase transitions in the Co-doped Heusler alloy Ni2Mn1−xCoxGa.

The phase transitions of a series of Co-doped Heusler alloys, Ni 2 Mn 1 − x Co x Ga (0 ⩽ x ⩽ 0.2), were investigated experimentally using the magnetization measurements, x-ray diffraction, and calorimetric measurements up to their respective melting points. With increasing Co concentration, the structural transition temperatures, Curie temperatures, and melting points, were observed to increase, while the order–disorder transition temperatures decreased. Temperature-dependent x-ray diffraction experiments revealed two different crystal structures in the low-temperature martensite phase for different Co concentrations. However, above their respective structural transitions, both low-temperature crystal structures transformed into the L2 1 cubic structure. These findings enabled the construction of a complete magnetic and structural phase diagram for Ni 2 Mn 1 − x Co x Ga, spanning from cryogenic temperatures to the melting points. The temperature-dependent XRD results revealed the abrupt changes in interatomic Mn–Mn distances, which validates the crucial role of Mn–Mn interatomic distance and the effect of the magnetic coupling competition in the structural stability between the martensite phase and austenite phase. [ABSTRACT FROM AUTHOR]