  Magneto-structural instability in the ferromagnetic shape memory alloy of
composition Ni$_2$Mn$_{1.4}$Sn$_{0.6}$ is investigated by transport and
magnetic measurements. Large negative magnetoresistance is observed around the
martensitic transition temperature (90-210 K). Both magnetization and
magnetoresistance data indicate that upon the application of an external
magnetic field at a constant temperature, the sample attains a field-induced
arrested state which persists even when the field is withdrawn. We observe an
intriguing behavior of the arrested state that it can remember the last highest
field it has experienced. The field-induced structural transition plays the key
role for the observed anomaly and the observed irreversibility can be accounted
by the Landau-type free energy model for the first order phase transition.
