The well-studied Ni-Mn-Ga system exhibits several drawbacks such as high brittleness and low working temperature (defined by martensitic transformation temperature T_m and Curie temperature T_C). The alloy systems Ni-Fe-Ga-Co and Ni-Co-Al are promising alternatives, as they are ductile and their working temperatures are similar or even higher compared to Ni-Mn-Ga. Here, we prepared both alloy systems by arc-melting. T_m and T_C were determined by DSC, SQUID magnetometer and VSM measurements and correlated with structural data.

For the quaternary Ni-Fe-Ga-Co, T_m and T_C can be tailored in a wide range by adjusting the composition and heat treatment. The effect of aging on the transition behaviour of a Ni₅₂Fe₁₇Ga₂₇Co₄ alloy was investigated. The magnetic transition in the annealed alloy exhibits a pronounced temperature hysteresis, indicating a coupled magnetostructural transition. Aging at 400°C leads to an increase of both hysteresis of the martensitic and the magnetic transitions. However, the martensitic transformation itself and the magnetic transition hysteresis disappeared after aging at 500 °C. The reason for this is the formation of γ precipitates, which suppress the occurrence of martensitic transformation.

For the ternary alloy Ni-Co-Al ten alloys with compositions Ni_32.5+XCo_39.5-XAl₂₈ and Ni_33.5+XCo_39.5-XAl₂₇ with X=0/0.5/1/1.5/2 were studied. Homogenisation was performed at 1300°C for 5 hours in a quartz ampoule filled with argon. Sample preparation for the subsequent measurements has a pronounced effect on the martensitic transformation. Simply crushing the samples in order to obtain small pieces for the measurements results in the absence of any martensitic transformation. A second annealing (again 1300°C 5h) yields T_m = 0-120°C, depending on composition. Further, two effects were found to have an influence on T_m, the quenching procedure after annealing and low temperature annealing during measurements. Moreover T_C=80-100°C is less dependent on composition.

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