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Properties and Structure of High Frequency Soft Magnetic Nano-composite Films
Shigehiro Ohnuma,Hiroshi Masumoto 한국자기학회 2011 Journal of Magnetics Vol.16 No.4
Metal-insulator type, nano-granular soft magnetic films have been reviewed from the viewpoint of high frequency magnetic materials. The formation of nano-granular structure is related to the magnitude of heat of formation of intergranule materials. Variation of the ratio of granule phase to intergranule phase in the film is found to produce various characteristics in the magnetic properties of the film. The HRTEM observation reveals that neighboring granules in the film with above 60 at.% Co, contact at considerable points and the films show soft magnetic properties which are explainable in terms of the random anisotropy model for nanocrystalline materials. Addition of Ni group elements in Co-O based films enhances their anisotropy field up to 400 Oe and they exhibit excellent frequency response of permeability. Also, large electromagnetic noise suppression effect is demonstrated as one of their potential applications.
Temperature Dependence of the Coercive Force of Ferromagnetic TM-Al-O (TM=Fe, Co) Granular Films
Shintaro Nakamura,Tsutomu Nojima,Akira yoshihara,Shigehiro Ohnuma 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The temperature dependence of the coercive force (Hc) of ferromagnetic TM–Al–O (TM=Fe, Co)granular films has been investigated in the temperature range from 290 down to 2 K. Fe–Al–O filmsshow weak anisotropy. In contrast, Co–Al–O films show clear in-plain anisotropy. The coerciveforces of Co–Al–O films show a logarithmic temperature dependence at low temperatures whilethose of Fe–Al–O films are almost independent of temperature.
Enhancement of Magneto-Optical Kerr Effect in Annealed Granular Films of Co-Au and $Co-AlO_x$
Abe, Masanori,Takeda, Eishi,Kitamoto, Yoshitaka,Shirasaki, Fumio,Todoroki, Norikazu,Gorodetzky, Gad,Ohnuma, Shigehiro,Masumoto, Tasuku,Inoue, Mitsuteru The Korean Ceramic Society 2000 The Korean journal of ceramics Vol.6 No.2
Co fine particles were dispersed in Au metal and $AlO_x$ amorphous matrices by vacuum evaporation and rf-sputtering, respectively, thus forming granular composite films having chemical compositions of $Co_{0.59}-Au_{0.41}$ and $Co_{0.52}/(AlO_x$)_{0.48}$. The films were annealed at 200~$500^{\circ}C$ to increase the size of the Co particles, from 30$\AA$ to 180$\AA$ in the Au matrix and 40$\AA$ to 180$\AA$ in the $AlO_x$ matrix, as revealed by X-ray diffraction analysis. The Co metal in as-deposited films have saturation magnetization equivalent to that of bulk Co, which is unchanged by the annealing, showing that the Co metal is not oxidized by the annealing. Magneto-optical Kerr rotation measured at $\lambda$=400-900nm for the $Co_{0.59}-Au_{0.41}$ film as deposited is larger than that calculated for the composition. The rotation increases as the film is annealed at $200^{\circ}C$ and $300^{\circ}C$, approaching to that of bulk Co. The Kerr rotation for the $Co_{0.52}-(AlO_x)_{0.48}$ film as deposited is smaller than that calculated for the composition based on Bruggeman effective medium theory. However, the rotation increases much, exceeding the rotation of the bulk Co as annealed at $300^{\circ}C$ and $400^{\circ}C$. As a possible origin of the marked magneto-optical enhancement a weak localization of light in granular structure is suggested.