Magnetocaloric effect in the low hysteresis Ni-Mn-In metamagnetic shape-memory Heusler alloy

"We have studied magnetocaloric properties of a Ni-Mn-In metamagnetic shape-memory alloy especially designed in order to display low thermal hysteresis. Magnetization and calorimetric measurements under a magnetic field have been used in order to determine isothermal magnetic field-induced entropy changes. Results obtained indirectly from magnetization data, quasi-directly from isofield calorimetric measurements, and directly from isothermal calorimetric runs are systematic and agree well with each other. We have analyzed the reproducibility of magnetocaloric properties with cycling from direct isothermal calorimetric measurements. Due to low thermal hysteresis, we have found that about 80% of the transition entropy change, ΔSt ≃ 25 J/kg K, can be reversibly induced under successive application and removal of a field of 6 T.

Elastocaloric and magnetocaloric effects in Ni-Mn-Sn(Cu) shape-memory alloy

"We have studied magnetocaloric and elastocaloric properties of a Ni-Mn-Sn(Cu) metamagnetic shape-memory alloy undergoing a magneto-structural transition (martensitic type) close to room temperature. Changes of entropy have been induced by isothermally applying both mechanical (uniaxial stress) and magnetic fields. These entropy changes have been, respectively, estimated from dilatometric measurements giving the length of the sample as a function of temperature at selected applied forces and magnetic fields and from magnetization measurements as a function of temperature at selected applied magnetic fields. Our results indicate that the elastocaloric effect is conventional and occurs in two steps which reflect the interplay between the martensitic and the incipient magnetic transitions. By contrast, the magnetocaloric effect is inverse and occurs in a single step that encompasses the effect arising from both transitions.

Caloric effects induced by magnetic and mechanical fields in a Ni50Mn25-xGa25Cox magnetic shape memory alloy

"We have studied the elastocaloric effect in a Co-doped Ni-Mn-Ga magnetic Heusler shape memory alloy in the vicinity of its martensitic transition. Measurements of the length change as a function of temperature have been carried out across the transition under applied compression stresses and magnetic fields. The isothermal stress-induced entropy changes have been computed from the experimental data. Results evidence a significant elastocaloric effect associated with the large entropy change of the structural phase transition. The alloy also exhibits a magnetocaloric effect at low applied magnetic fields. It is shown that application of a magnetic field below 1 T increases the estimated elastocaloric relative cooling power by about 20%. A comparison of elasto-and magnetocaloric properties indicates that a similar relative cooling power is reached under application of 10 MPa or 0.8 T.