Antiferromagnetic Domain Structure Research Articles

Visualization of antiferromagnetic domain structures on as-grown NiO crystals by optical methods

The antiferromagnetic T-domain structures on a bulk NiO crystal surface could be visualized by means of incident-light types of microscope such as a differential interference microscope, a phase-contrast microscope and a high-dispersion interference contrast method. The visualization of the antiferromagnetic domain is possible due to the facial tilt which was induced in the NiO crystal due to the antiferromagnetic ordering below the Neel temperature. The lateral resolution of the present methods in visualization of the domain structure is about 1μm, which is better than that of X-ray or neutron topography. The tilt angle between each domain was measured by two-beam interferometry; the average experimental value (9′23″) agrees fairly well with the calculated value (8′24″). Direct observation of the movement and disappearance of the domain boundaries upon heating could also be carried out under the phase-contrast microscope.

Memory effects of the antiferromagnetic domain structures in MnF2

Memory effects of the antiferromagnetic domain structures in MnF₂

Behaviour of antiferromagnetic domains in KNiF 3

The antiferromagnetic domain structure of KNiF 3 is described. Wall motion in fields up to 1 T has been studied down to 4.2 K using synchrotron radiation for X-ray topography. Néel's theory of wall motion has been directly verified and the effective magnetocrystalline anisotropy energy deduced to be 18±2 Jm -3 at 4.2 K.

The influence of domain structure on the magnetic properties of hematite

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Fluxed-melt growth of nickel oxide crystals and their electrical properties

Nickel oxide crystals prepared at temperatures near the melting point by the Verneuil and d.c. arc methods contain excess oxygen. The electrical properties of such crystals are dominated by impurity band conduction associated with the excess oxygen. NiO containing excess oxygen is black, while stoichiometric material is green in colour. Crystals of nickel oxide were grown by cooling their solution in PbF 2 (approximate ratio NiO:PbF 2 is 1:40 by weight) at 2 °C/hr from 1290 to 800åC. The cooling process was accompanied by much evaporation of the flux. Octahedra with almost perfect terminal {111} faces, up to 6 mm on edge, were produced from a 500 cm 3 crucible. Thin regions of the crystals were green by transmitted light. These flux-grown crystals exhibit less strain and are more regular in their anti-ferromagnetic domain structure than crystals produced by flame-fusion or d.c. arc techniques. Measurements of the electrical conductivity and frequency dependence of permitivity show that NiO grown from a fluxed melt is nearly stoichiometric. The magnetic susceptibility of such NiO is 2% lower than that of flame-fusion material. It is shown that the presence of excess oxygen also increases the magnetic susceptibility.

The antiferromagnetic domain structure of epitaxial nickel oxide

Epitaxially grown nickel oxide single crystals (thickness 10 to 200 μm) have been examined below the Neel temperature (523° K) by optical and X-ray diffraction topographic techniques. The antiferromagnetic domain structure in the as-grown crystals is extremely complex and sensitive to crystal thickness. Annealing simplifies the domain structure, but the presence of the magnesium oxide substrate is shown to inhibit the formation of the large domains observed in well-annealed Verneuil-grown crystals. The misorientation between adjacent domains has been measured by a direct technique and shown to be consistent with the theoretical value.

Electron microscopic observation of order twins and anti-phase boundaries in tetragonal NiMn

The microstructure of the low temperature phase of NiMn has been examined by transmission electron microscopy. It was found that the ordered alloy has a twinned structure which minimizes the strains induced by ordering. The individual crystals are further fragmented by anti-phase boundaries. The presence of a twinned structure implies also a fragmentation into an anti-ferromagnetic domain structure.

Exchange Anisotropy and Strain Interactions in the Ni-NiO System

The interactions between Ni and NiO were investigated by examining the magnetic properties of Ni films on single-crystal NiO substrates. The orientations of the NiO substrates were (001) (compensated spin planes), and (111) (parallel spin planes). With (001) NiO the Ni films were strained an amount corresponding approximately to the rhombohedral deformation of NiO below its Néel temperature. The amplitude and symmetry of magnetic torque data were consistent with the magnitude of this strain and the symmetry of the antiferromagnetic domain structure, respectively. Ni films on (111) NiO substrates had a complex field dependence of rotational hysteresis. This behavior was analyzed in terms of exchange anisotropy coupling and the interaction of the field with both the Ni and NiO spin systems. The analysis provided good agreement with the data for an exchange anisotropy energy of 1.75 erg/cm2 of interface, a crystalline anisotropy of NiO in its parallel spin plane of 1.1×103 erg/cc NiO, and a ``flop field'' for NiO in its parallel spin plane of 5 to 10 kOe. The analysis showed that two new regions of rotational hysteresis loss are present in fields ≥ the ``flop field'' of the antiferromagnetic spin system. Some more general features of exchange anisotropy coupling are also discussed.

Magnetomechanical damping in chromium

Abstract Damping hysteresis observed with changing temperature and strain-amplitude below ∼40°c end a marked reduction of strain-amplitude-dependent damping in this region when a biasing tensile stress is present, is consistent with the suggestion that an antiferromagnetic domain structure exists in chromium below ∼40°c.