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Department of Physics Engineering*nonmember

Fluctuation Spectrum of Director in Cholesteric Phase with External Field, M. Yamashita: Mol. Cryst.
Liq. Cryst. 409, pp. 219-227, 2004.
Fluctuation spectrum of molecular orientation in the cholesteric phase exposed to the external
field with positive anisotropy is calculated for the general case of Frank's elastic constants. The
stability of the phase is certified in the meaning of Peierls-Landau theory.

The Order and the Polarisation of the System Composed of Polar Gay-Berne Molecules with Bend, T.
Miyazaki* and M. Yamashita: Mol. Cryst. Liq. Cryst. 413, pp. 117-124, 2004.
NVT molecular dynamics simulation is carried out to study the relation of molecular shape anddipole moment to the liquid crystalline ordering at the system of coupled Gay-Berne molecules which
are dimers of two types of Gay-Berne particles coupled by harmonic spring at each end. The
appearances of polarization and biaxiality together with the location of clearing temperature arereported for various types of combination of position and direction of the dipole attached to molecule.

Ordering in Chiral Smectics at Freely Suspended Film, M. Yamashita: Ferroelectrics 309, pp. 63-73,
2004.
The method to study phase transitions of thin systems on the basis of the bulk phase diagram isapplied to a freely suspended film of ferroelectric smectics showing a first order phase transition in thebulk, where the ordering effect due to surface layers is replaced by an effective field which is conjugate
to the order parameter. In the framework of a phenomenological free energy, whose coefficients are
determined form the experimental evidence about C7, behaviours of transition are clarified, whichcoincides with experimental findings, and especially the small shift of transition temperature from thebulk one is elucidated. The continuous change occurring in the system of thickness just below a critical
thickness is proved to be achieved by an insertion of an unstable state of the interior layers, which isnever realised in the bulk. This mechanism of continuous change shows the difference between theordering effects due to the boundaries and external fields.

Isotropic, Nematic and Smectic A Phase Behaviour in a Fictitious Filed, M. Torikai and M. Yamashita:
J. Phys. Soc. Jpn., 73, pp. 2154-2157, 2004.
Phase behaviours of liquid crystals under external fields, conjugate to the nematic order andsmectic order, are studied within the framework of mean field approximation developed by McMillan.
It is found that phase diagrams, of temperature vs interaction parameter of smectic A order, show
several topologically different types caused by the external fields. The influences of the field conjugate
to the smectic A phase, which is fictitious field, are precisely discussed.

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Nematic Ordering of a Liquid Crystalline Homeotropic Cell, M. Yasen, M. Torikai and M. Yamashita: J.
Phys. Soc. Jpn., 73, pp. 2453-2457, 2004.
Nematic ordering in a very thin system under the homeotropic anchoring condition is studied in
the framework of the Maier-Saupe model. Nonuniformity due to the boundary effect is described interms of an effective field which is conjugate to the order parameter, and behaviour of the system isanalysed by observing loci of the effective fields on the phase diagram of the bulk. A continuous change
occurring at the system with thickness just smaller than a critical thickness is shown to be mediatedby an unstable state; a metastable high-temperature phase changes to a metastable low-temperature
one continuously via an unstable phase between them. This mechanism is an analogue of thephenomenon occurring in a freely suspended film of a certain chiral smectic material.

Critical behavior near the metal-insulator transition in the one-dimensional extended Hubbard model
at quarter filling, Kazuhiro SANO, Yoshiaki Ono* : Phys. Rev. B70, pp.155102-1--155102-6, 2004.
We examine the critical behavior near the metal-insulator transition (MIT) in the
one-dimensional extended Hubbard model with the on-site and the nearest-neighbor interactions U
and V at quarter filling using a combined method of the numerical diagonalization and therenormalization group(RG). The Luttinger-liquid parameter (Kr ) is calculated with the numerical
diagonalization for finite size systems and is substituted into the RG equation as an initial condition to
obtain Kr in the infinite size system. This approach also yields the charge gap in the insulating statenear the MIT. The results agree very well with the available exact results for U=infinity even in thecritical regime of the MIT where the characteristic energy becomes exponentially small and the usual
finite size scaling is not applicable.

Antiferromagnetic Exchange Coupling in RE-TM Films, Akira Inagaki, Masaya Tsuneoka, Atsushi
Ohshima, Tadashi Kobayashi, Yuji Fujiwara, Shigeru Shiomi and Tsutomu Shiratori*: J. Magn. Soc.
Jpn., 28, pp.312-317, 2004.
This paper reports the magnetic and magneto-optical properties of antiferromagnetic exchange
coupled (AFC) RE-TM double layered films prepared by sputter deposition. The sample structure is
glass/underlayer
Ru/Gd-Fe-Co/(E-layer
Fe-Co)/AFC
layer
Ru/(E-layer
Fe-Co)/Gd-Fe-Co/protectivelayer Ru. The exchange coupling energy J was found to depend on Ru
thickness of the AFC layer. The first AFC peak was found at an AFC layer thickness of 3.0 Å. Next we
inserted a thin Fe-Co layer called the E-layer, between the AFC layer and the magnetic layer toimprove the J value. In AFC RE-TM double layered films, a complicated Kerr loop was observed wheneach magnetic layer was thin. Then we compared the calculated result with the experimental result todistinguish the ferromagnetic coupling from the AFC. Next we investigated thermal stability of J.
Wall Structure and Energy on DWDD, Atsushi Ohshima, Kentaro Kusano, Tadashi Kobayashi, Yuji
Fujiwara, Shigeru Shiomi and Masahiko Kaneko*: Trans. Magn. Soc. Jpn., 4, pp.152-155, 2004.
Wall structure and energy have been simulated for the Domain Wall Displacement Detection

A―51(DWDD), and the front process and the rear process under temperature gradient have been
considered. For the front process, when the mark length is comparable with the domain wall width in
the displacement (D) layer, the domain copied on the D-layer from the memory layer collapses. By
making the D-layer thin, the minimum mark length for which the domain wall displacement occurs
can be shortened. For the rear process, we confirmed that by inserting the control layer between the
D-layer and the switching layer, the mark length with which the ghost signal is suppressed becomes
longer. By making the anisotropy energy constant in the D-layer increase, improvement in the DWDD
process is expected.

Noncollinear magnetism phenomena induced at surface domain walls and in vortex cores of magnetic
quantum dots, A. J. FREEMAN*, Kohji NAKAMURA, Tomonori ITO : Journal of Magnetism andMagnetic Materials 272-276, pp. 1122-1127, 2004.
We report noncollinear magnetism phenomena by means of several recent examples: (a)enhancement of magnetocrystalline anisotropy in ferromagnetic (FM) Fe films by intra-atomic
noncollinear magnetism, (b) noncollinear magnetic structures of domain walls in FM Fe andantiferromagnetic NiMn, and (c) curling spin and orbital structures in the vortex core of an Fe
quantum dot, as obtained from the first principles full-potential linearized augmented plane wave
method including noncollinear magnetism with no shape approximation for the magnetization. These
results are in good agreement with experiments, and give new information about magnetic phenomena
at surfaces and in nanostructures.

Noncollinear magnetism and enhancement of magnetocrystalline anisotropy at the Σ3(111) grainboundary in ferromagnetic Fe, Kohji NAKAMURA, Tomonoi ITO, A. J. Freeman*, L. Zhong*, J. F.
Castro* : Applied Physics Letters 84 , pp. 4974-4976, 2004.
Magnetic structures and magnetocrystalline anisotropy of the Σ3(111) grain boundary (GB) in
ferromagnetic Fe are investigated by the first-principles full-potential linearized augmented
plane-wave method including intra-atomic noncollinear magnetism. In breaking the spatialtranslation symmetry in a crystalline solid, GB is found to give rise to a magnetic noncollinearity,
where the magnetic moments at both sides of the GB orient at a angle about 10° with respect to eachother. Importantly, the presence of the GB enhances the magnetocrystalline anisotropy energy by one
order of magnitude from its bulk value and may induce a pinning effect on the magnetization rotationor magnetic domain wall motion.

Atomically sharp magnetic domain wall in thin films Fe(110): A first principles noncollinear
magnetism study,
Kohji NAKAMURA,, Yoshifumi TAKEDA, Toru AKIYAMA, Tomonori ITO, A. J.
Freeman* : Physical Review Letters 93, pp.057202-1-4, 2004.
Magnetic domain wall structures in an Fe(110) monolayer are determined by the highly precise
firt principles full-potential linearized augmented plane-wave method including intra-atomic
noncollinear magnetism. The self-consistent results demonstrate that the magnetization changes fromone orientation to the opposite (180°) orientation within 8 Å width without any abrupt rotation. This

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narrow domain wall is found to arise from band effects. Our results are consistent with and support
domain walls having a 6 Å width recently observed in spin-polarized scanning tunneling microscopy
experiments.

Magnetic structures and out-of-plane magnetic anisotropy at the exchange bias interface: Co/FeMn,
Kohji NAKAMURA, Tomonori ITO, A. J. Freeman* : Physical Review B 70, pp. 060404(R)-1-4, 2004.
The magnetic structures and anisotropy at the compensated ferromagnetic/antiferromagnetic
Co/FeMn interface are investigated by the highly precise first principles full-potential linearized
augmented plane-wave method that incorporates intra-atomic noncollinear magnetism in order tounderstand the magnetic complexity involved in the spin-flop coupling and the presence of intra-atomic
noncollinear magnetism. The self-consistent results predict that the Fe moments in the FeMn layer
reorient away from their directions in bulk FeMn so as to be parallel to the Co moment direction – areorientation that induces an out-of-plane magnetic anisotropy. These results appear to support andconfirm recent experimental x-ray magnetic circular dichroism findings that rule out spin-flop couplingas the mechanism for exchange bias in this system.

Modern computational magnetism: role of noncollinear magnetism in complex magnetic phenomena,
A. J. FREEMAN* and Kohji NAKAMURA: Physica Status Solidi (b) 241, pp. 1399-1405, 2004.
Modern computational magnetism continues to grow at an accelerating pace stimulated by new
and exciting discoveries important for basic science and technological applications. Here, we review
some recent important progress made in treating complex noncollinear magnetic phenomena arisingfrom the breaking of symmetry at surfaces, interfaces, and nanostructures, by means of our newly
generalized first principles full-potential linearized augmented plane wave (FLAPW) method fornoncollinear magnetism with no shape approximation to the magnetization. Because of space
limitations, we restrict our report illustrate results of the noncollinear magnetic structures induced at
the FM NiFe/AFM NiMn interfaces, in the domain walls of FM Fe and AFM NiMn, and in the vortex
cores of a Fe quantum dot. These results are in good agreement with experiments and give new
information about magnetic phenomena at surface, interfaces, and in nanostructures.

Systematic theoretical investigations of adsorption behavior on the GaAs(001)-c(4x4) surfaces,
Tomonori ITO, Kazumi TSUTSUMIDA, Kohji NAKAMURA, Yoshihiro KANGAWA*, Kenji
SHITRAISHI*, Akihito TAGUCHI*, Hiroyuki KAGESHIMA* : Applied Surface Science 237, pp.
194-199, 2004.
Adsorption behavior on the GaAs(001)-c(4x4) surfaces is systematically investigated by using
our ab initio-based approach and the Monte Carlo methods. The change in stable structure of thec(4x4) surfaces is clarified by considering adsorption or desorption of surface dimers as functions oftemperature and As pressure. The calculated results imply that the c(4x4) surface with As dimers is
stable at low temperatures less than ~400 K, whereas the surface with Ga-As dimers is stabilized athigh temperatures in the range of ~400 K to ~700 K. The disordered dimer arrangements consistingof Ga and As substituted by each other in the c(4x4) unit cell hardly appear even at high temperatures

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such as ~800 K. We also investigate the behavior of Ga and As adatoms on these c(4x4) surfaces. The
calculated results reveal that Ga atoms can adsorb and migrate on the surfaces while desorption of As
adatoms proceeds without sufficient migration.

Theoretical investigations of adatom behavior on non-planar surfaces with GaAs(n11)A, Koichi
ASANO, Yoshihiro KANGAWA*, Hirotoshi ISHIZAKI, Toru AKIYAMA, Kohji NAKAMURA,
Tomonori ITO : Applied Surface Science 237, pp. 206-212, 2004.
The behavior of Ga and As adatoms on non-planar surfaces consisting of GaAs(001)-(2x4) andGaAs(n11)A (n=2, 3 and 4) surfaces are investigated by empirical interatomic potentials with the aidof ab initio calculations. The calculated results imply that Ga adsorption energies strongly depend on
the surface orientation, whereas As adsorption energies keep almost constant. The difference inadsorption energies can be interpreted by considering strain energy. In particular, Ga adatom isstabilized on the (311)A surface by the smallest strain energy forming interatomic bonds with three As
atoms located at the regular fcc sublattice. Furthermore, we roughly simulate resultant surface profile
of GaAs thin films on the non-planar surfaces consisting of the (001)-(2x4) top and (n11)A side surfaces
based on the rate equation. The simulated results reveal that the non-planar surface with (311)A sidesurface forms the linear surface profile.

First-principles analyses of O2 molecules around ultrathin SiO2/Si(100) interface, Toru AKIYAMA,
Hiroyuki KAGESHIMA*, Tomonori ITO : Japanese Journal of Applied Physics 43, pp. 7903-7908,
2004.
The microscopic structures and reaction mechanisms of O2 molecules at ultrathin SiO2/Si(100)interface are investigated based on first-principles total-energy calculations. It is found that themolecular-type oxygen is stable in the SiO2 region of the interface, while the O2 in the Si substratedissociates and two Si-O-Si bonds are formed. It is also found that the O2 in the SiO2 region candirectly react with the Si substrate. The energy barrier for its reaction (0.2 eV) does not correspond to(previously consented) serving process of interfacial Si-Si bonds, but to the formation of weak Si-O
bonds between the O atoms of oxidant and the interfacial Si atoms: The hybridization of theoxygen-2p orbitals of the oxidant and the valence band states of the Si substrate is the principal factorof the reaction. The calculated results imply that other microscopic mechanisms such as accumulationof interfacial strain or its release mechanisms are involved in the interfacial reaction during Si
oxidation.

Theoretical study of excess Si emitted from Si-oxide/Si interface, Hiroyuki KAGESHIMA*, Masashi
UEMATSU*, Kazuto AKAGI*, Shinji TSUNEYUKI*, Toru AKIYAMA, Kenji SHIRAISHI* : Japanese
Journal of Applied Physics 43, pp. 8223-8226, 2004.
The excess Si emitted from the Si-oxide/Si interface is studied using the first-principles
calculations. It is shown that the excess Si can have many (meta-) stable positions around the interface.
In addition, some positions in the oxide do not have any dangling bonds or floating bonds in contrast to
those in the bulk crystalline Si. The results indicate that the emitted Si can be located in the oxide layerA―54

but they do not necessarily cause charge traps in the oxide. The emitted Si atoms are thought to just be
oxidized and absorbed into the oxide while a portion of them cause the E’ centers, the Pb centers or
charge traps.

Thermodynamic stability for group IV alloy semiconductors [in Japanese]. Tomonori ITO, Yoshihiro
KANGAWA* : Journal of the Japanese Association for Crystal Growth 31, pp. 4-11, 2004.
Thermodynamic stability of group IV alloy semiconductors such as Si1-x-yGexCy solid solutions inbulk and thin film states is systematically investigated by excess energy calculations based on
empirical interatomic potentials and Monte Carlo (MC) simulations. In bulk state, the calculated
excess energies for Si1-x-yGexCy have positive values over the entire concentration range. This implies
that Si1-x-yGexCy with a random distribution of Si, Ge and C is thermodynamically unstable at 0 K.
Furthermore, the excess energies of Si1-x-yGexCy increase with Ge content x when C content y remains
constant. This is because an increase of Ge content introduces large strain energy in Si1-x-yGexCy. In
thin film state, although lattice constraint at the interface reduces the excess energies by 20-30 % of
those in bulk state, we obtain similar results to those in bulk state. Further MC simulation reveal that
Ge atoms segregate in the topmost layer and C atoms accumulate in the second layer.

Plastic Deformations of Micro-Spheres by Solidified Lubricants and Lubricants' Shear Characteristics
under Very High Pressure (Part 1) − Observation of Plastically-Deformed Micro-Spheres − [inJapanese], Yuichi NAKAMURA, Yutaka ISHIBASHI* and Yasushi KUROSAKI: Tribologist, 49-6, pp.
518-524, 2004.

Fractal analysis of adhesion on tool surface in compression of aluminum strips by using AFM [inJapanese], Masahito MATSUI, Yasushi KUROSAKI and Yusuke MIYAUCHI: Journal of Japan
Institute of Light Metals, 54-1, pp. 9-13, 2004.
Adhesion properties in simple compression of aluminum strips are analyzed in the
micro/nanometer range by employing the zeroset and power spectrum fractal analyses. An atomic
force microscope (AFM) is used to estimate the fractal dimensions. It is found that the adhesion andtool and specimen surfaces have fractal structure. Various fractal dimensions obtained for theadhesion and tool and specimen surfaces are compared to each other and discussed. When the surface
roughness of tool is same, the ratio of the total adhesion area depends on the fractal dimension.
Though the AFM apparatus is difficult to distinguish the adhesion particles from the tool surface, thepower spectrum dimension has possibility of distinguishing the adhesion particles from the tool
surface. Finally, a method for computer simulation of the nanometer scale surface structure ispresented, and satisfactory images are constructed.

Nanofractal Analysis on Material Surfaces Using AFM, Mir Behdad Khamesee, Yasushi Kurosaki,
Masahito Matsui and Kenichi Murai: Materials Transactions, 45-2, pp. 469-478, 2004.
The surface structures of four materials (a pure aluminum sheet, an aluminum alloy sash, aA―55

thickness gauge and a magnetic tape) are observed on the nanometer scale by atomic force microscopy(AFM) and analyzed by one-dimensional fractal analyses. It is confirmed for all the surfaces that they
have a self-affined fractal property under a resolution of 1nm. The two-dimensional fast Fouriertransformation (2D-FFT) analysis is also applied to these surfaces and their characteristics areclarified. The power spectrum model for surface simulation is proposed and its validity is confirmed byexperimental results. A method for simulating surface structure of any materials is presented, and its
validity is shown on some materials whether in-plane isotropic or anisotropic. A computer aided
engineering (CAE) system composed of 2D-FFT and inverse FFT (IFFT) for quantitative estimation of
surface nanostructures is advanced and applied to various surface problems. It enables the mass dataof material surface to compress into only three parameters.