  In this paper, we present temperature and field dependent neutron diffraction
(ND) study to unravel the structural and the magnetic properties in
Ni50Mn38Sb12 Heusler system. This alloy shows martensitic transition from high
temperature austenite cubic phase to low temperature martensite orthorhombic
phase on cooling. At 3 K, the lattice parameters and magnetic moments are found
to be almost insensitive to field. Just below the martensitic transition
temperature, the martensite phase fraction is found to be 85%. Upon applying
the field, the austenite phase becomes dominant, and the field induced reverse
martensitic transition is clearly observed in the ND data. Therefore, the
present study gives an estimate of the strength of the martensite phase or the
sharpness of the martensitic transition. Variation of individual moments and
the change in the phase fraction obtained from the analysis of the ND data
vividly show the change in the magneto-structural state of the material across
the transition.
