Giant magnetic-field-induced strain in NiMnGa seven-layered martensitic phase

TLDR

X‑ray diffraction shows the phase is nearly orthorhombic with lattice parameters a = 0.619 nm, b = 0.580 nm, c = 0.553 nm, and mechanical and magnetic‑anisotropy measurements confirm twin‑boundary motion under magnetic field. The seven‑layered martensitic phase exhibits a giant 9.5 % strain at ambient temperature under <1 T, driven by magnetic‑field‑controlled twin‑boundary motion and associated with a seven‑layer shuffling‑type modulation along (110)[11̄0]p.

Abstract

Giant magnetic-field-induced strain of about 9.5% was observed at ambient temperature in a magnetic field of less than 1 T in NiMnGa orthorhombic seven-layered martensitic phase. The strain proved to be caused by magnetic-field-controlled twin boundary motion. According to an analysis of x-ray diffraction data, the crystal structure of this phase is nearly orthorhombic, having lattice parameters a=0.619 nm, b=0.580 nm, and c=0.553 nm (in cubic parent phase coordinates) at ambient temperature. Seven-layer shuffling-type modulation along the (110)[11̄0]p system was recorded. The results of mechanical tests and magnetic anisotropy property measurements are also reported.