  Polycrystalline Ni-Co-Mn-Sn based ferromagnetic shape memory alloys (FSMAs)
show promise as actuator materials, but their practical application involving
magnetic field induced strain (MFIS) is often limited by three factors: the
requirement for high magnetic fields (> 5 T), martensitic transition
temperature away from room temperature, and limited recovery of pre-strain
applied to the martensite phase. Current work investigates the martensitic
transition (MT) and shape memory effect under the application of magnetic field
for bulk polycrystalline Ni37Co11Mn43Sn9 alloy. The outcome of the study
reveals a metamagnetic transition from the martensitic phase to the austenitic
phase at a low field of 2.8 T at 300 K which results 0.25% spontaneous MFIS.
Interestingly, 1.3% pre-strained specimen registers a 100% recovery with the
application of magnetic field of 4.5 T. Furthermore, the pre-strained specimen
exhibited a two-way shape memory effect between a strain value of 1.0% to 1.55%
during the field loading and unloading sequences. Notably, this study also
demonstrates, to the best of our knowledge , for the first time, that the
spontaneous strain and pre-strain add together. This finding paves the way for
achieving a giant MFIS by pre-straining a Ni-Mn-Sn/In class of FSMAs which
shows large spontaneous MFIS.
