Crystal Structure of Ferromagnetic Nickel Oxide

Abstract

The determination of crystal structure was performed on the ferromagnetic nickel oxide obtained by the flame fusion method. Apart from a slight deviation of axial angle from 90°, it has a defect tetragonal structure belonging to the space group I 4 1 / amd ( D 4 h 19 ), the lattice constants being a =5.899 6 kX. and c =8.343 4 kX. (\(c/a{=}\sqrt{2}\)) at 31 .5 °C. Considering the deviation, the structure must be altered to a monoclinic one belonging to C 2/ m ( C 2 h 3 ), the lattice constants being a =5.104 4 kX., b =2.951 5 kX., c =2.948 2 kX. and β=125°11 .4 ' at the same temperature as above. The details of the atomic arrangements in both cases are given in the last column of Table 8. The saturation magnetization estimated under an appropriate assumption for the spin alignment agrees fairly well with the observation. Thus the comparison of the present structure with that of the ordinary nickel oxide may give us a peek into one of the processes of transition from an antiferromagnetic state to a ferromagnetic one.