Microstructural and In Situ Lorentz TEM Domain Characterization of As-Quenched and γ’-Precipitated Co49Ni30Ga21 Monocrystal

The article concerns the rarely described magnetic domain structure of Heusler alloys in the case of a single crystal [100]-oriented Co-Ni-Ga alloy. The structure of the magnetic domains of the alloy was compared in two states: in the quenched and additionally aged state. Ageing led to precipitation of the spherical phase γ’ nanoparticles (Co-rich, FCC lattice with a = 0.359 nm). Lorentz transmission electron microscopy observation methods combined with cooling and in situ heating of the sample in the transmission electron microscope in the temperature range from 140 K to 300 K were combined to observe the magnetic domain structure. Significant differences in the dimensions and morphology of magnetic domain boundaries have been demonstrated. The quenched sample showed no change in stripe domain structure when the aged sample showed significant development of branching magnetic structures. This may be due to a change in the chemical composition of the matrix resulting from a decrease in cobalt and nickel content at the expense of precipitations.