Sequence of structural and magnetic transitions in Ni48Co2Mn39Sn11 shape memory alloy

The structural and magnetic transitions in Ni48Co2Mn39Sn11 shape memory alloy were systematically investigated. During cooling, the paramagnetic austenite transforms into paramagnetic martensite at T-M similar to 375 K, followed by a gradual transition from paramagnetic to superparamagnetic martensite around T-S similar to 320 K. Upon further cooling through T-P similar to 100 K, the superparamagnetic clusters collectively freeze into a superspin glass state as corroborated by aging, rejuvenation, and memory effects. Consequently, the unique transition sequence of paramagnetic austenite --> paramagnetic martensite --> superparamagnetic martensite --> superspin-glass martensite is disclosed. (C) 2011 Elsevier BY. All rights reserved.