Intermartensitic transitions and phase stability in Ni50Mn50-xSnx Heusler alloys

Ni-Mn based Heusler alloys are of considerable interest due to their multifunctional properties such as magnetic shape memory, magnetocaloric effect and spintronics. The reason for these multifunctional properties is the presence of a first order martensitic transition and its strong coupling to the magnetization. In this work, one of the outstanding class of martensitic Heuslers, Ni-Mn-Sn, is investigated in relation to magneto-structural phase transitions and the stability of the various crystallographic structures under varying temperature. Temperature-dependent X-ray diffraction, resistance and magnetization measurements on Ni50Mn50-xSnx alloys are performed in a broad valence electron concentration range 7.91 <= (e/a) <= 8.34 (5.1 <= x <= 20.3 at.%). The results reveal that in addition to the austenite-martensite transition, further intermartensitic transitions take place with decreasing temperature. Depending on the composition, we observe that the parent martensite phase tends to transform to L1(0) martensite as the ground state phase when the temperature is lowered. A phase diagram of Ni50Mn50-xSnx is constructed to include intermartensitic phase transition boundaries. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.