Internal stress dependent structural transition in ferromagnetic Ni–Mn–Ga nanoparticles prepared by ball milling

Ni–Mn–Ga nanoparticles were prepared by ball milling technique. X-ray diffraction pattern of the milled powders has a broad peak near the location of the prominent peak for the Heusler phase of Ni2MnGa, indicating very disordered structures with small particle sizes. Structural properties of milled Ni–Mn–Ga particles recover to those of the bulk state after appropriate annealing temperature. It is worth noting that particles with size above 50 nm exhibit martensitic transformation. The average internal stress was calculated to be 2.83–1.13 MPa stored in the distorted lattice. Saturation magnetization of the milled sample increases with annealing temperature due to re-crystallization and grain growth.