Papers by Author: Hiroshi Sakurai

Abstract: Magnetic Compton profiles (MCPs) of Co/Au multilayers have been measured and analyzed by DV-Xα cluster model calculations from a viewpoint of perpendicular magnetic anisotropy (PMA). The PMA and the MCPs are discussed for the presently obtained results for Co/Au, along with the previously obtained results for Co/Pd and Co/Pt. A Co/Au multilayer shows a weak PMA which is caused by |m|=1 states of Co 3d electrons at a smooth Co/Au interface. The increase of the interface-to-volume ratio plays the main role in determining the perpendicular anisotropy in Co/Au multilayers. The strain of a Co layer can have a secondary role in determining the magnetic anisotropy in Co/Au multilayers, although the strain dominates PMA in the case of Co/Pd and Co/Pt multilayers.

Abstract: We have studied the coercive force of fine magnetic CoPt dot enhanced by nanometer-sizing of the dot. The 39-to 106-nm-sized CoPt magnetic dot arrays were formed by30-keV-electron beam (EB) drawing with thin calixarene resist and 200-eV-Ar ion milling. Using the fine magnetic dot arrays, we measured coercive forces of the dot by x-ray magnetic circular dichroism (XMCD) with an energy of 11.56 keV, which corresponds to an energy edge of Pt-L3. It is experimentally demonstrated that a coercive force of the nanometer-sized magnetic column increased as the dot diameter decreased. Keywords: Coercive force, nanomagnetic column, XMCD, magnetic storage, EB lithography

Abstract: Mn_0.7Zn_0.3Fe₂O₄ is synthesized by sintering the nanosize precursor with sintering aids, which is synthesized by the coprecipitation method. The crystal growth of Mn_0.7Zn_0.3Fe₂O₄ is controlled by the amount of sintering aids. Complex permeability is explained by the Maxwell-Garnett (MG) effective medium model. The ferromagnetic resonance frequency more than 1 GHz can be explained by the shape anisotropy under the sintering process of the Mn_0.7Zn_0.3Fe₂O₄ particles. These results suggest possibility of Mn_0.7Zn_0.3Fe₂O₄ as a high frequency device material.

Abstract: Mn_1-xZn_xFe₂O₄ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) are synthesized using sintering coprecipitation method. The coprecipitation retains from 0 hours to 48 hours at 1200 °C. The synthesis of a Mn_0.6Zn_0.4Fe₂O₄ is almost completed even though retaining time is for 0 hours at 1200 °C. The crystal growth of Mn_0.6Zn_0.4Fe₂O₄ particles proceeds rapidly retaining up to 6 hours and saturates retaining more than 6 hours at 1200 °C. The permeability and the electric resistivity are affected by the crystal growth of Mn_0.6Zn_0.4Fe₂O₄ particles.

Abstract: sotropic and directional autocorrelation functions have been calculated using the DV-Xα method on polyethylene type clusters to investigate the effect of its characteristic dimensionality of the wavefunctions. Directional autocorrelation functions are calculated along the c-axis, the direction of the long chain of carbon atoms, and along an axis perpendicular to it. The analysis of the molecular orbital dependence of the autocorrelation function reveals that the long range order along the c-axis can be enhanced as increasing the length of the cluster and the orbitals near the highest occupied molecular orbital have a key role for the one-dimensional order.

Abstract: sotropic and directional autocorrelation functions are calculated for 14 electron diatomic molecules, N₂, CO, and BF, using the DV-Xα method. In order to investigate the effect of chemical bonds for the molecules, directional autocorrelation functions parallel and perpendicular to the bond are investigated. The anisotropies of the directional autocorrelation functions of N₂ and CO are different from the anisotropy of BF, which has a wave shape.

Abstract: The effects of strain and interface roughness at the Co/Pd interface are investigated from the viewpoint of perpendicular magnetic anisotropy (PMA) using the DV-Xα cluster model calculation method. It is found that spin projected occupation number ratio of magnetic quantum number |m| = 2 for the Co 3d electrons enhances by expanding the lattice within a close-packed plane of fcc stacking and, hence, enhances the PMA. Rough interface decreases the spin projected occupation number ratio of |m| = 2 and, hence, decreases the PMA. These results explain the PMA properties of Co/Pd multilayers fabricated using molecular beam epitaxy (MBE) technique and RF sputtering techniques.

Abstract: Isotropic and directional Compton profiles are calculated for 14 electron diatomic molecules, N₂, CO, and BF, using the DV-Xα method. In order to investigate the effect of chemical bonding for Compton profiles, parallel and perpendicular directional Compton profiles to the molecules are calculated and compared with the results from Hartree-Fock and configuration interaction methods. The DV-Xα method could describe the more detailed character of covalent bonding than that of ionic bonding.

Abstract: Compton profiles related to the electron momentum distribution are calculated using the DV-Xα method for a series of rare gases from He to Rn. To verify the criteria of the DV-Xα-derived Compton profiles, our results are compared with those obtained from the Hartree-Fock method. The trend of Compton profiles obtained from the DV-Xα method is discussed.

Abstract: We compare two Co/Pd multilayers with correspondingly smooth and rough interfaces. The first is a Co (1.5 nm)/Pd (2.6 nm) multilayer with a smooth interface deposited by the MBE technique, and the second is a Co (1.6 nm)/Pd (4.0 nm) multilayer with a rough interface deposited by the sputter technique. Both multilayers have almost the same perpendicular magnetic anisotropy energy, 1.15 Merg/cc for the Co (1.5 nm)/Pd (2.6 nm) multilayer and 1.20 Merg/cc for the Co (1.6 nm)/Pd (4.0 nm) multilayer, respectively. The symmetry of the wave function, which is measured using the magnetic Compton profile, is almost the same for both multilayers. This suggests that the smooth interface controls the wave function and enhances the PMA energy even if the Co/Pd multilayer has a thinner Pd layer.