Transport, magnetic and structural investigations of Co–Ni–Al shape memory alloy

The transport, magnetic and structural properties of the ferromagnetic shape memory alloy with nominal composition Co1.28Ni1.17Al have been investigated. The alloy shows long range ferromagnetic order below 269 K. The anomaly due to the martensitic transition is observed in the resistivity and magnetization data in the temperature range around 175 K, which is associated with clear thermal hysteresis. A significant magneto-thermal irreversibility between the zero-field-cooled and the field-cooled data is observed below the martensitic start temperature. The structural change is confirmed by temperature dependent X-ray diffraction, and our analysis indicate that both martensite and austenite phases mutually coexist in the region of hysteresis. Existence of distinct minor hysteresis loops in the resistivity data is also in accordance with a metastable region of phase coexistence across the martensitic transition.