(a)  Mg-Ni

(b) Mg-Ni-H

(c) Mg-Ni

Figure 2: X-ray diffraction patterns of Mg-Ni ultrafine-particles (a), Mg-Ni ultrafine particles after hydrogen absorption at 400°C, 4 MPa, (b), and Mg-Ni ultrafine particles after hydrogen desorption (c).