Susumu Takemoto

Ferromagnetic Resonance of Electrically Conductive Manganese Ferrites

Resonance experiments have been performed between 77–350 K at 9.3 GHz on single crystal spheres of manganese ferrite of low resistivities (0.1∼0.3Ω cm at room temperature). The linewidth shows a maximum at a temperature from 100 K to 200 K, with a marked dependence upon the sample size as well as upon the resistivity of specimen. A characteristic deviation of the resonance field in from that expected by Kittels formula is also noted. Detailed description is given to show the observed results to be attributable to an eddy current effect rather than due to the so-called slow or fast relaxation mechanisms. The linewidth maximum is interpreted to occur in a temperature region over which the excitation of resonant mode varies from “surface type” to “volume one” corresponding to the change in skin depth.

Antiferromagnetic Domain Structures in Vapour-Grown NiO (111) Platelets Containing Growth Twins

Domain structures are examined on ribbon-shaped (111) platelets of NiO crystals containing thin lamellae twinned on the (111) plane with respect to each other. Together with configurations of T-domains realized across the twin planes detailed configurations of T-walls are determined by optical and X-ray observations. Characteristics of observed T-domain structures can be reasonably interpreted by considering the elastic interaction between T-walls and twin planes through the rhombohedral striction as well as the anisotropic shape of specimen.

Resonant Modes in FMR of Low Resistivity Ferrites

Resonance experiments at 9.3 GHz have been performed for cylindrical rods of manganese-zinc ferrite of low resistivity (∼0.3 \(\varOmega\) cm at 300 K), with dc magnetic field parallel to their axis. For an appropriate value of rod radius, the surface and volume type resonant modes are excited in different dc magnetic fields on the same sample and at the same temperature, resulting in two distinct peaks on the absorption curve. The results make it clearer how the skin depth affects the anomalies in the resonance properties of electrically conductive manganese ferrites. The description is made in connection with the results reported previously for spherical samples.

Excitation Mechanisms in Pulsed Ar-Kr Discharges

Excitation mechanisms of Ar–Kr ion lasers have been investigated by observing time sequences of spontaneous emissions from upper laser levels in the pulsed discharge mode. The experimental results show that a dominant excitation mechanism of Ar gas in Ar–Kr mixtures changes, with increasing Kr content, from direct electron collisions into excitation transfer collisions between Kr ion and Ar atom. The excitation mechanism of Kr gas is predominantly due to a direct electron excitation and no appreciable change with the gas composition is found.