Influence of annealing on magnetic field-induced structural transformation and magnetocaloric effect in Ni–Mn–In–Co ribbons

A study of the magnetic field-induced martensitic transformation and magnetocaloric effect in Ni₄₅Mn₃₇In₁₃Co₅ and Ni₄₆Mn₃₅In₁₄Co₅ ribbons prepared by melt-spinning was carried out. Annealing significantly increases the degree of ordering in the austenite phase, reduces the critical field and hysteresis of the magnetically induced martensitic transformation and increases the magnetically induced shift of martensitic transformation temperatures. For the most In-rich sample, Ni₄₆Mn₃₅In₁₄Co₅, annealing at 900 °C for 2 h leads to the formation of Co-rich face-centered cubic γ precipitates. The Curie temperature of the γ phase is about 370 K. The formation of the second phase has little impact on the hysteresis, but broadens the transformation interval and reduces the magnetic entropy change.