Macroscopic pattern formation preceding martensitic transformation in a ferromagnetic shape memory alloy Ni₅₁ Fe₂₂ Ga₂₇

This paper reports a macroscopic pattern formation that occurs before the onset of a martensitic transformation in a ferromagnetic shape memory alloy, Ni51 Fe22 Ga27. Electron holography studies reveal that the magnetic flux pattern in the parent (cubic) phase changes dramatically with cooling. Interestingly, the flux pattern developed in the parent phase is inherited by the martensitic (monoclinic) phase. Observations of the diffuse electron scattering indicate that the change in the magnetic flux pattern is triggered by a lattice anomaly, which appears to produce a long-range strain field in the parent phase.