Masumi Sato

Magnetically induced phase separation and magnetic properties of Co–Mo hexagonal-close-packed structure thin films

Magnetically induced phase separation along the Curie temperature in the hexagonal-close-packed phase of a Co–Mo binary system has been predicted by thermodynamic calculations. Furthermore, the phase separation and magnetic properties of Co–Mo sputtered thin films have been investigated. Nanoscale compositional fluctuation caused by the magnetically induced phase separation has been confirmed in the films deposited on a heated substrate in the same manner as Co–Cr-based alloys. The magnetic anisotropy constant of the Co–Mo films is larger than that of Co–Cr films. From these results, it is concluded that the Co–Mo system is promising for use as a base alloy system for high density recording media.

Direct observation of magnetically induced phase separation in Co-W sputtered thin films

Phase separation of Co-W sputtered thin films having a large magnetocrystalline anisotropy energy have been investigated. A nanoscale compositional fluctuation caused by magnetically induced phase separation was directly confirmed in the films deposited on a heated substrate in analogy with Co-Cr-based alloys. The difference between the phase separation features in Co-W and Co-Cr is attributed to the difference in their elastic energy. It is expected that the phase separation is enhanced by selecting optimum sputtering conditions. The Co-W system, therefore, is considered to be a promising candidate as a base alloy system for high-density recording media.

Co-Mo and Co-Mo-Cr alloy thin films promising for magnetic recording

Phase separation behavior of Co-Mo thin films and magnetic anisotropy energy of Co-Mo and Co-Mo-Cr thin films deposited on Cr(112)//MgO(110) single crystal substrates have been studied by using an analytic transmission electron microscope and a vibrating sample magnetometer. The results show that the phase separation does happen in the Co-Mo thin films, resulting in Mo-rich phase surrounding Co-rich magnetic grains, similar as that in the Co-Cr system. However, the Mo-rich phase still shows the ferromagnetic characteristic at room temperature due to its not so high Mo content. The first order anisotropy constants of the Co-Mo thin films are about double that of the Co-Cr thin films in the composition range of 4.0-14.0 at.%Mo (or Cr). With the addition of Cr into the Co-8.7 at.%Mo thin film, the magnetic anisotropy constants show no obvious deterioration, but it results in the increase of anisotropy field.

Excitation of Helical Wave in the Positive Column

Both the experimental and the theoretical studies on the controlled excitation of the helical wave are made in weakly ionized mercury, helium and neon discharge cylindrical plasmas with a longitudinal magnetic field below the critical field value. The phase constant of the excited wave has almost linear relation with exciting frequency and becomes larger as the applied uniform magnetic field increases. The attenuation constant has a peak value near the critical frequency and the attenuation of the wave becomes smaller with increasing magnetic field. These relations are analysed theoretically as a kind of an electron drift resistive wave. The comparison of the experimental results with the calculated ones is in good agreement.

TRANSITION FROM A MOVING STRIATION TO A HELICAL OSCILLATION IN A POSITIVE COLUMN

A transition from a moving striation to a helical oscillation was observed in the positive column of a helium discharge at a pressure of 0.4 mm Hg as an applied longitudinal magnetic field was increased. The frequency and amplitude of the moving striation decreased with increasing magnetic field. When the magnetic field reached a critical value of about 1650 G, a helical oscillation appeared and the two waves were observed to coexist. The striation disappeared with a further increase of the field, but the helical oscillation continued to exist.

OBSERVATION OF THE CRITICAL MAGNETIC FIELD BY LIGHT INTENSITY FROM A POSITIVE COLUMN.

The light intensity of a positive column in a longitudinal magnetic field changes with the field and becomes minimum at the critical field when a helical oscillation appears in the positive column. As this change is very steep at the critical point, even when the longitudinal electric field does not clearly show the point, an observation of the light intensity of the positive column may be useful in detecting the critical field value.

Collision Diffusion of Plasma in Magnetic Field

Diffusion rate of a plasma across a magnetic field lower than the critical field for screw instability is measured and is compared with Simons diffusion theory which states that the diffusion of the plasma across the longitudinal magnetic field is not ambipolar in short discharge tubes. Mathematical treatment of the plasma state equation shows that the short circuit path to neutralize space charge pointed by Simon can not be made up in the plasma. A new measuring method by means of the voltage-current relation of the discharge tube in the magnetic field is introduced to determine the diffusion rate across the magnetic field quantitatively. According to the present investigations, there is no diffusion mechanism due to so called “short circuit effect,” and the diffusion is ambipolar independent of the tube dimension.

Hyperfine field of156Gd in TbFe2, TbFe3, TbCo2 and TbCo3 compounds

Time integral γ-γ angular correlation measurements have been made on156Gd in Tb-3d metal compounds, TbFe2, TbFe3, TbCo2 and TbCo3, using two Ge(Li) detetctors. From the observation of a linear relation between magnetic hyperfine fields at Gd and Tb nuclei in corresponding compounds, it is inferred that crystalfield induced variations of the Tb moment are negligible. The experimental results are discussed in terms of the conduction electron polarization caused by the magnetic moment of 3d metals.

Moving striation and. helical oscillation in a positive column

This paper reports co-existence of the moving striation and the helical oscillation in the positive column in a longitudinal magnetic field. The existing regions for these oscillations are graphically obtained in relation to the magnetic field and the electric field of the column and the experimental results of the co-existence can be explained by the graph. In very short tube, thee is no critical magnetic field therefore no helical oscillation but instead the moving striation up to very large magnetic field. The striation is also affected by external conditions such as discharge current, heater current etc.

Observation of the critical magnetic field by light intensity

Light intensity of a positive column in a longi tudinal magnetic field changes with the field and becomes minimum at the critical field value when the helical oscillation appears in the positive column. As this change is very steep at the critical point even when the longi todinal electric field does not clearly show no point, the observation of the light intensity of the positive column may be useful for the detection of the critical field value.