  The fascinating multiple magnetic states observed in the Ni-Mn-Sn based
metamagnetic shape memory alloy are addressed through a combined muon spin
relaxation (muSR) and neutron powder diffraction studies. The material used in
the present investigation is an off-stoichiometric alloy of nominal
composition, Ni[2.04]Mn[1.4]Sn[0.56]. This prototypical alloy, similar to other
members in the Ni-Mn-Sn series, orders ferromagnetically below T[CA] (= 320 K),
and undergoes martensitic type structural transition at T[MS] (= 290 K), which
is associated with the sudden loss of magnetization. The sample regains its
magnetization below another magnetic transition at T[CM] = 260 K. Eventually,
the composition shows a step-like anomaly at T[B] = 120 K, which is found to
coincide with the blocking temperature of exchange bias effect observed in the
alloy. In our study, the initial asymmetry A_[10] ) of the $\mu$SR data falls
rapidly below T[CA], indicating the onset of bulk magnetic order. A[10] regains
its full asymmetry value below T[MS] suggesting the collapse of the
ferromagnetic order into a fully disordered paramagnetic state. Below the
second magnetic transition at T[CM], asymmetry drops again, confirming the
re-entrance of a long range ordered state. Interestingly, A[10] increases
sluggishly below T[B], indicating that the system attains a disordered/glassy
magnetic phase below T[B], which is responsible for the exchange bias and
frequency dispersion in the ac susceptibility data as previously reported. The
neutron powder diffraction data do not show any magnetic superlattice
reflections, ruling out the possibility of a long range antiferromagnetic state
at low temperatures. The ground state is likely to be comprised of a
concentrated metallic spin-glass in the backdrop of an ordered ferromagnetic
state.
