[en] Several wet and dry methods for the conversion of UF₆ to UO₂ powder, e.g., the ammonium diuranate (ADU) process and the integrated dry route process, have been developed to an industrial scale. Although the UO₂ powders fabricated by conventional methods have good ceramic characteristics, there is room for improvement. To extend burnup of nuclear fuel, a decrease in fission gas release from UO₂ pellets is required. It has been considered that large-grain pellets satisfy this requirement, but it is difficult to obtain such large-grain pellets by using conventional UO₂ powder. A new method has been developed to produce a highly active UO₂ powder that can greatly contribute to improvement of the fabrication process of nuclear fuel pellet. By using this highly active UO₂ powder, large-grain pellets can be made easily, and low-temperature sintering can be achieved

[en] The relationship between crystallographic grain orientation and the three kinds of surface energy components; dispersion, polar, and hydrogen bonding components, in Co₇₃Cr₁₈Pt₆Ta₃ perpendicular magnetic recording media with an amorphous C or a Ti₉₀Cr₁₀ underlayer was discussed. Each surface energy component of the thin film was calculated from an extended Fowkes theory by measuring the contact angle of a test liquid on the thin film. The experimental results revealed that the polar component of surface energy of the Co₇₃Cr₁₈Pt₆Ta₃ magnetization film with the C underlayer affected greatly the Co [0 0 1] preferred orientation of the Co₇₃Cr₁₈Pt₆Ta₃ magnetization film, while the surface energy of the Co₇₃Cr₁₈Pt₆Ta₃ magnetic layer with the Ti₉₀Cr₁₀ underlayer had little influence on the distribution of it

[en] The multi-chamber slab-shape fluidized bed reactor is being developed in Mitsubishi Material Corporation for the conversion of UO₃ to UF₆ especially toward the recycle use of reprocessed uranium. The design feature of the new reactor is the adoption of slab-shape for the reactor and the partition of the reactor interior to several sub-chambers. It enables substantial reduction in size of conversion process equipments, and thus contributes to the reduction of the conversion costs. (author)

[en] Reversed single magnetic bits of 130 nm in diameter were successfully written in a CoNi/Pt multilayered film by means of magnetic probe recording. A weak exchange coupled layer deposited onto a stronger exchange coupled layer effectively induces a local magnetic reversal, which results in the formation of small and stable magnetic bits

[en] Amorphous C and Si films were sputter-deposited as underlayers of Co/Pd multilayer perpendicular magnetic recording media. The magnetic properties of the media were significantly affected by the underlayer thickness; namely, the values of coercivity H_c and nucleation field -H_n increased and the value of α decreased with merely increasing the thickness of C or Si underlayer, where α is the derivative of M-H loop at the value of coercivity. The coercivity was not always affected by magnetic anisotropy constant K_u for the Co/Pd media. In read-write experiments, the higher S/N ratio was obtained for the media with the thicker C or Si underlayer, which exhibited low α and high H_c. In the time decay experiments of magnetization, the Co/Pd multilayer media with C or Si underlayer possessed good thermal stability. This study demonstrated that the introduction of C or Si underlayer greatly improves magnetic properties, read-write characteristics, and thermal stability of Co/Pd multilayer perpendicular magnetic recording media

[en] Signal and noise characteristics of Co/Pd multilayer perpendicular magnetic recording media are discussed based upon MFM analysis. The noise of the Co/Pd multilayer media is originated mainly from irregularities in the magnetic transition regions, and can be drastically suppressed by increasing the thickness of the carbon underlayer although a large number of reversed magnetic domains between the magnetic transitions still exist. The fine magnetic clusters formed in the medium with a thick carbon underlayer result in clear magnetic transition boundaries of recorded bits in the high recording density region. By examining the profile of the M-H loops, the decrement in the α value, which is defined as the slope of M-H loop at the value of coercivity, improves the signal to noise (S/N) ratio for the Co/Pd multilayer media

[en] The effect of amorphous carbon underlayer thickness on the microstructure of the Co/Pd multilayer perpendicular magnetic recording media was investigated. From the magnetic force microscopy observation in the AC-demagnetized state of the Co/Pd multilayer media, the magnetic cluster size was observed to effectively decrease with an increase in carbon underlayer thickness, where the higher coercivity and the higher S/N ratio of the Co/Pd multilayer media were obtained with the thicker underlayer. Furthermore, the distribution of [1 1 1] orientation of FCC-Pd became broader, and the grain size decreased with an increase in the carbon underlayer thickness. These effects caused the magnetic exchange decoupling of Co/Pd multilayer media. We suggested that the change of microstructure was directly related to the surface roughness of the amorphous carbon underlayer

[en] Effects of the introduction of a Pd/Si dual seedlayer on the microcrystalline structure and magnetic properties of [Co/Pd]_n multilayered perpendicular magnetic recording media were investigated. The Pd/Si dual seedlayer was composed of a Pd upper seedlayer and a Si under seedlayer. The Pd upper seedlayer with a thickness of up to 10 nm markedly increased the coercivity of [Co/Pd]_n multilayered media in the direction perpendicular to the film surface. The highest coercivity of 7.8 kOe was obtained for the [Co/Pd]₁₀ medium with a Pd (10 nm)/Si (100 nm) dual seedlayer. The Pd upper seedlayer not only facilitated the formation of regular interfaces between the Co and Pd layers, but also reduced the thickness of the deteriorated initial layer in the [Co/Pd]_n multilayer, resulting in enhancement of the magnetic anisotropy field. The [Co/Pd]_n multilayered medium with the Pd/Si dual seedlayer exhibited weak intergranular exchange coupling between [Co/Pd]_n grains, which led to excellent read-write characteristics

[en] The possibility of magnetic probe recording into a continuous perpendicular medium is discussed. By applying a current from the tip to the medium, a very localized area can be heated and bits as small as 80 nm in diameter could be written. This value is close to the calculated minimum diameter of reversed cylindrical domains in our perpendicular medium. A current can be injected directly from the tip to the medium by means of a current source, or one can use capacitive currents. We prefer the first method, since the current, and therefore the heating process, can be controlled more precisely. The energy required to write a bit is in the order of 1 nJ. Calculations show that most of the heat is dissipated at the tip end. Demagnetizing fields of the surrounding material play an important role and are so strong that bits can be written without applying an external field. By decreasing the film thickness, the demagnetizing fields are reduced, and selective overwriting of previously written bits could be demonstrated

[en] We present our results on the development of magnetic sensors for application in magnetic probe recording. Successful writing experiments on a magnetic medium with perpendicular anisotropy show that magnetic domains of 130 nm can be reversed in a heat-assisted process. For reading purposes we propose a magnetoresistive sensor. The optimization of the shape of the sensor was performed using micromagnetic simulations with the requirement that the sensor has to be capable of both read and write operations. At this stage, the experimental realization of the sensor was carried out at a wafer-base level. The fabrication technique consists of a combination of optical lithography and focused ion beam etching