All-d-metal Ni(Co)-Mn(X)-Ti (X = Fe or Cr) Heusler alloys: Enhanced magnetocaloric effect for moderate magnetic fields

All-d-metal Ni(Co)-Mn-Ti Heusler alloys show high magnetocaloric/barocaloric effects ascribed to the oc-currence of a martensitic transformation together with excellent mechanical properties. However, high magnetic fields are needed to fully drive the transformation and to obtain their maximum responses. To further tune the martensitic transition and the associated magnetocaloric response, we systematically in-vestigate the role of partial Mn substitution by Fe or Cr on the parent composition Ni36Co14Mn35Ti15. On the one hand, Cr doping increases the entropy change of the transformation but causes a tighter overlap of both martensitic and Curie transitions. This significantly reduces the magnetization difference between austenite and martensite and, consequently, strongly decreases the magnetocaloric response. On the other hand, Fe doping reduces the entropy change of the transformation and separates both martensitic and Curie tran-sitions while keeping the magnetization difference among both phases. These two combined features re-duce the magnetic field needed to completely drive the martensitic transformation and leads to higher and broader isothermal entropy change peaks for moderate magnetic field changes, reaching up to 25% en-hancement for 2 T when compared to the undoped alloy.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

All-d-metal Ni(Co)-Mn-Ti Heusler alloys exhibit high magnetocaloric/barocaloric effects due to the occurrence of a martensitic transformation and excellent mechanical properties. By partially substituting Mn with Fe or Cr, the martensitic transition and magnetocaloric response can be further regulated. Cr doping increases the entropy change but reduces the magnetization difference, while Fe doping reduces the entropy change but maintains the magnetization difference. The Fe-doped alloy requires lower magnetic fields to initiate the transformation and shows higher and broader isothermal entropy change peaks.