Influence of Co on Structure and Magnetic Properties of Ni_50−xCo_xMn₂₉Ga₂₁ Shape Memory Alloy Ribbons

In this work, we investigated the influence of Co on the structure and magnetic properties of Ni50−xCoxMn29Ga21 (x = 0, 2, 4, 6, and 8) shape memory alloy ribbons fabricated by using the melt-spinning method. The addition of Co increases the formation of the austenitic crystalline phase in the alloy ribbons. The crystalline grains in rod-shapes with diameter of ∼2 µm and length of ∼10 µm are mostly oriented perpendicular to the ribbon surface. The martensitic-austenitic transformation was performed on both the thermomagnetization and differential scanning calorimetry methods. With the increase of Co concentration, the martensitic-austenitic structural phase transformation temperature (TM-A) of the alloy gradually decreases while the Curie temperature of the austenite phase (TCA) of the alloy increases from 355 K (for x = 0) to 432 K (for x = 8). Besides, the martensitic-austenitic phase transformation is also significantly affected by the external magnetic field. The structural phase transformation temperature of the alloy tends to shift towards lower temperatures as the external magnetic field increases.