Magnetization and high resolution neutron powder diffraction measurements have been made on the magnetic shape memory alloy Ni1.84Mn 1.64In0.52. The compound undergoes a broad structural phase transition, which on heating starts at ∼150K and finishes at ∼215K. On cooling there is a ∼20K hysteresis. The high temperature parent phase is cubic (a=5.988 Å) with the L21 structure in which the excess Mn atoms occupy the vacancies on the Ni and In sites. The magnetic moment is located mainly on the Mn atoms with the same magnitude on both the 4a (Mn) and 4b (In) sites. The low temperature martensite is monoclinic with parameters a=4.405(2), b=5.553(2), c=12.950(2)Å, β=86.47(10)° and space group P2/m. The magnetic properties of the martensitic phase are complex and indicate metamagnetic behaviour.
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