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Understanding the origin of the magneto-caloric effects in substitutional Ni-Mn-Sb-Z (Z=Fe, Co, Cu) compounds: insights from first-principles calculations

Ni-Mn based ternary Heusler compounds have drawn attentions lately as significant magneto-caloric effects in some of them have been observed. Substitution of Ni and Mn by other $3d$ transition metals in controlled quantity have turned out to be successful in enhancing the effect and bring the operational temperatures closer to the room temperature. Using density functional theory calculations, in this work, we have systematically explored the roles of various factors such as site occupancies, magnetic interactions, and compositions associated with the constituents of Mn-excess Ni$_{2}$MnSb Heusler compounds upon substitution of Ni and/or Mn by $3d$ transition metals Fe, Co and Cu. Our calculations unveiled the physics behind the variations of physical properties associated with the magneto-caloric effects, and thus interpreted the available experimental results successfully. The work also provided important information on the compounds and the composition ranges where significant magneto-caloric effects may be realised and further experimental investigations need to be done.