The Role of defects and internal stresses on tuning the multifunctional properties of Metamagnetic Shape Memory AlloysThursday (27.09.2018) 09:30 - 09:45 S1/03 - 223 Part of:
The influence of defects and local stresses on the martensitic transformation (MT) and magnetic properties has been analyzed in Ni-Mn-Sn and Ni-Mn-Sn-Co alloys at both macroscopic and atomic scale level. Even without modifying the atomic order, it is shown that slight microstructural distortions brought by soft milling can be used to properly tune the MT, and, as a result, their related multifunctional properties. In Ni-Mn-Sn alloys, anti-phase boundaries linked to dislocations promote the antiferromagnetic coupling between the Mn atoms, which ultimately affect the MT and the magnetic properties . Besides, the evolution of the magnetization saturation has been discussed in terms of the density of the non-magnetic inclusions (defects) . Upon annealing, as long as the non-magnetic inclusions decrease, both the MT characteristics and the nanoscale magnetism are enhanced. The recovery-process of the microstructure has been characterized by Differential Scanning Calorimetry and 119Sn-Mossbauer spectroscopy (119Sn-MS). The recovery of the MT, in fact, can be directly tracked by monitoring the non-magnetic component revealed by 119Sn-MS (see Figure 1a) . Moreover, the nanoscale magnetism is investigated as a function of the microstructural state in Co doped alloys in both austenite and martensite phases, Figure 1b. In contrast to the ternary alloy, in Ni-Mn-Sn-Co alloys the presence of defects, far for worsening, enhance the magnetocaloric effect comparing with its annealed counterpart . These results show the potential of 119Sn-MS in order to quantify the overall contribution of defects to the MT, opening the door to the thermomechanical control, of the otherwise hardly tunable functional properties of Ni-Mn-Sn and Ni-Mn-Sn-Co alloys.
 I. Unzueta, J. López-García, V. Sánchez-Alarcos, V. Recarte, J. I. Pérez-Landazábal, J. A. Rodriguez-Velamazán, J. S. Garitaonandia, J. A. García and F. Plazaola, Applied Physics Letters 100, 181908 (2017)
 J. López-García, I. Unzueta, V. Sánchez-Alarcos, V. Recarte, J. I. Pérez-Landazábal, J. A. Rodriguez-Velamazán, J. A. García and F. Plazaola, Intermetallics, 94, 133-137 (2018)
 V. Sánchez-Alarcos, V. Recarte, J. I. Pérez-Landazábal, J. López-García, I. Unzueta, J.J. Beato-López, J. A. García, F. Plazaola and J. A. Rodriguez-Velamazán, Submitted to APL Materials