Study of phase transitions and mesoscopic magnetic structure in Ni-Mn-Ga by means of small-angle polarized neutron scattering

Abstract Results of measuring small-angle neutron scattering (SANS) and neutron depolarization in Ni 49.1 Mn 29.4 Ga 21.5 single crystal in a wide range of temperatures and magnetic fields are presented. The characteristic temperatures of the alloy were found to be as follows: T C =373.7 K and the martensite transition temperature T m =306 K. It was shown that SANS below T C has magnetic nature and it is adequately described by the relationship I m = A ( q 2 + κ 2 ) −2 ( q is the scattering vector, R c =1/ κ is the correlation radius) at close up T C and T T C . It is suggested that SANS at T m T T C is due to magnetic decoration of nucleations of new martensite phase in process of phase transition and that percolation-type phase transition is evidently observed at T m . Temperature and field dependence of left–right asymmetry in the scattering of neutrons polarized along or opposite to the applied field which is due to the inelastic magnetic interaction of neutrons in the sample was observed and discussed.