Fabrication and magnetic properties of In2O3/NiMnGa core-shell nanowires

We have prepared composite nanowires consisting of In2O3 and NiMnGa, in which the In2O3 core was coated with a continuous layer of NiMnGa via pulsed laser deposition technique. We have verified the tubular structure of NiMnGa shell by means of transmission electron microscopy (TEM). X-ray photoelectron spectroscopy revealed the presence of Ni, Mn, and Ga elements and TEM-energy-dispersive X-ray spectroscopy indicated that these elements resided mainly in the shell region. Since X-ray diffraction patterns and lattice-resolved TEM images showed no crystalline NiMnGa phase, with scanning electron microscopy revealing that the shell is sufficiently thick (~ 55 nm), we suggest that the shell layer is amorphous. The ferromagnetic behavior, in terms of coercive field, remanent magnetization, and saturation magnetization in the hysteresis loop, was considerably enhanced by coating the In2O3 core with a NiMnGa shell layer, at the measurement temperature of 300 K as well as 5 K. We have carried out a comparison study for revealing the mechanisms, by which the ferromagnetism was enhanced by the shell-coating. Although the annealing-induced changes of In2O3 core cannot be ruled out, the presence of NiMnGa phase played a decisive role in enhancing the ferromagnetic behavior of composite nanowires.