Elastocaloric Effect Associated with Different Types of Martensitic Transformations: Typical First-Order and Weak First-Order Ones

Elastocaloric effects of a Ni50Fe19Ga27Co4 alloy exhibiting a typical first-order martensitic transformation (MT) and an Fe-31.2Pd (at.%) alloy exhibiting a weak first-order MT, respectively, have been compared using their single crystals. A flat region appears in the temperature dependence of elastocaloric effect in the Ni50Fe19Ga27Co4 alloy, while such region is missing in the Fe-31.2Pd alloy. The elastocaloric effect of the Ni50Fe19Ga27Co4 alloy originates essentially from the latent heat released by the stress-induced MT, while that in the Fe-31.2Pd alloy originates essentially from the entropy change caused by elastic deformation of the parent and martensite phases. Although the Young's modulus in the [001] direction at Ms is nearly the same for the two alloys (E ∼ 2 GPa), its slope dE/dT is largely different between the two alloys. It is approximately 0.003 GPa K−1 for the Ni50Fe19Ga27Co4 alloy and 0.2 GPa K−1 for Fe-31.2Pd alloy.