Effect of Al doping on the martensitic transition and magnetic entropy change in Ni–Mn–Sn alloys

Martensitic phase transformations and magnetocaloric effect in Al co-sputtered Ni–Mn–Sb alloy thin films

“…There have been reports that the decrease of unit cell volume due to doping increases the martensitic transformation temperatures [30]. Hence, it can be concluded that the decrease in the Ni-Mn distance and a corresponding decrease of cell volume are only factors responsible for increasing T M in our Ni-Mn-Sb-Al thin films.…”

“…It is noted that, the FH curve does not retrace the FC curve and a thermal hysteresis width was observed in all samples. The presence of this thermal hysteresis indicates the presence of first-order structural transition [30]. On the other hand, the absence of thermal hysteresis near T A C indicates a second order magnetic transition from FM to PM state.…”

“…A monotonic increase in the martensitic transformation temperatures with increasing Al concentration could be easily seen in the Table 1. It has been reported in Ni-Mn-X (X = Sn, In and Sb) FSMAs that the T M increases with an increase in the value of valence electron concentration (e/a) [23] and decrease of unit cell volume [30]. In addition, the hybridization between the Ni atoms and the Mn atoms on the X sites is also an important driving force for the martensitic transformation in Mn-rich Ni-Mn-X Heusler alloys [21,29].…”

“…In addition, the hybridization between the Ni atoms and the Mn atoms on the X sites is also an important driving force for the martensitic transformation in Mn-rich Ni-Mn-X Heusler alloys [21,29]. While using the extended x-ray absorption fine structure (EXAFS) studies and first-principles calculations of Ni-Mn-In full Heusler alloys, it has also been suggested that the Ni-Mn hybridization may be responsible for the magnetic properties [30]. In such cases, once the Ni-Mn hybridization is established, any change in the Ni or Mn concentration will weaken the hybridization, leading to the shift of martensitic transformation.…”

“…The presence of smaller hysteresis widths in sample A1, A2 and A3 as compared to A0 indicates thermo elastic phase transformations in Ni-Mn-Sb-Al thin films. It means that the deformation energy during the martensitic phase transformations was elastically stored in the twin morphology of the martensitic structure and therefore less energy was consumed for phase transition in these films [30]. This can decrease the phase transition response time of materials as a result these materials could be working as actuators and sensor.…”