Yasumitsu Shimomura

X-Ray Diffraction Study on CoO

Low temperature x-ray diffraction experiment were performed to investigate the crystal symmetry of antiferromagnetic CoO and its domain structure. A new rhombohedral deformation was found in addition to the well known tetragonal deformation. The experimental result is consistent with the magnetic structure found by Roth, and can be interpreted by Kanamoris theory. Two types of magnetic domains were found to exist in CoO, as are expected from the magnetic structure and the related lattice deformations.

On Nickel Oxides of High Oxygen Content

Nickel oxides of high oxygen content formed by incomplete dissociation of nickel nitrate were investigated crystallographically and magnetically. The oxygen excess of these oxides ranges from zero to 0.2 gr. atom/mol., and their crystal structures are not essentially different from that of the ordinary nickel oxide. As they are not in a stable state, they have some curious but important behaviors. That is, with the degree of excess, they become to have a cubic structure the parameter of which is larger than that ( a ) of a rhombohedrally deformed one, and at sufficiently high oxygen contents they behave as something like a ferromagnetics. Such rather extraordinary phenomena may be considered to be originated from the fact that the oxygen excess in the specimens owes not only nickel vacancies but also the absolute excess of anions. In the measurements of susceptibility, the coincidency between the heating and cooling curves is very good for ferromagnetics-like oxides, while it is not for antiferromagnetic ...

Some Physical Properties of Nickel Oxides

Variation of the magnetic susceptibility, electric resistivity and specific heat with temperature have been observed for various nickel oxides containing different amounts of copper. The anomaly temperatures of these properties and also of their lattice generally differ from one another. Among these temperatures the last one is the lowest and the magnetic one is the highest, and the higher is the copper content the larger is the difference. It may be concluded from these results that the deformation of nickel oxide must be originated from the antiferro-magnetic exchange interaction as proposed by Greenwald and Smart, 4) but at the same time it seems to be affected by the other factors e.g. the ionic radius ratio and the vacancies.

Precipitates with a Defect Structure in Thin Film of NiO

Thin films of single crystal of NiO are prepared by the method initiated by Cech and Alessandrini. The films are heated at 1400~1600°C in air and are examined by means of electron microscopy and electron diffraction. Many coherent particles of a second phase with characteristic shapes appear in the matrix film of NiO. They have a defect structure of Ni-deficient NiO, which is of spinel-type. Growth and morphology of the precipitates are observed and discussed.

FMR Study on NiFe2O4 Precipitates in NiO Containing Fe Ions

Ferromagnetic resonance measurements were performed on NiFe 2 O 4 precipitates formed in single crystals of NiO containing Fe ions. It is concluded that the rhombohedral deformation of NiO below its Neel temperature is propagated into the NiFe 2 O 4 precipitates and thus a uniaxial anisotropy is induced magnetomechanically in the precipitates besides the well-known cubic anisotropy. Furthermore, it is indicated that exchange interaction of spins across the interface between NiFe 2 O 4 precipitates and the NiO matrix is also important at the early stage of the precipitation.

Some Preliminary Electron Microscope Observations on NiO Bombarded by Ions or Electrons

From electron micrographs and the corresponding diffraction patterns obtained for NiO bombarded by ions (air, 1~2 kv.) or electrons (100 kv.), the following results have been obtained. (1) Images of ion damages are similar to those in other substances and can be annealed out at 1200°C in air. Lamellar structure (spacing: ~50 A) and superlattice reflections are sometime detected in the annealed specimens. (2) Microstructures of the electron bombarded NiO can be classified into the following four types: (a) The annealed structure. (b) The aggregation of thin (in or [001]) crystallites. (c) The dense distribution of Ni particles (several hundred A in diameter) over the (001) surface of NiO with the orientation: (001)Ni//(001)NiO, [100]Ni//[100]NiO. (d) The coarser distribution of larger Ni particles, which keep orientation relationships of a pair of spinel twins among themselves.