2024/02/27 更新

写真a

ツノダ ヨリヒコ
角田 頼彦
所属
理工学術院
職名
名誉教授
学位
博士(理学) ( 大阪大学 )

所属学協会

  •  
     
     

    日本中性子科学会

  •  
     
     

    日本金属学会

  •  
     
     

    日本物理学会

研究キーワード

  • 固体物性Ⅱ(磁性・金属・低温)

  • Metallic System)

  • Solid State Physics (Magnetism

 

共同研究・競争的資金等の研究課題

  • メスバゥアー効果を用いた磁性の研究

  • 中性子散乱による固体物性の研究

  • Neutron Scattering

Misc

  • Magnetic diffuse scattering of neutrons in an ordered Fe3Pt Invar alloy

    Yorihiko Tsunoda, Masao Takasaka, Syusuke Hosoda

    PHYSICAL REVIEW B   80 ( 13 ) 134407  2009年10月

     概要を見る

    Using an ordered Fe72Pt28 Invar alloy single-crystal, spin modulations due to the local lattice distortions in the premartensitic embryos were studied by neutron scattering. Magnetic diffuse scattering caused by the modulations of spin structure was found around the (1 0 0) and (1 1 0) super-lattice points. The diffuse scattering intensity caused by the spin modulations is far stronger than that due to the lattice displacement of the localized spins. The spin modulations extend to wider space than the cluster sizes with the lattice distortion. Relations are discussed between the spin modulations and the various anomalous magnetic behaviors reported by previous authors as common properties of the Invar alloys.

    DOI CiNii

  • Magnetic diffuse scattering of neutrons in an ordered Fe3Pt Invar alloy

    Yorihiko Tsunoda, Masao Takasaka, Syusuke Hosoda

    PHYSICAL REVIEW B   80 ( 13 ) 134407  2009年10月

     概要を見る

    Using an ordered Fe72Pt28 Invar alloy single-crystal, spin modulations due to the local lattice distortions in the premartensitic embryos were studied by neutron scattering. Magnetic diffuse scattering caused by the modulations of spin structure was found around the (1 0 0) and (1 1 0) super-lattice points. The diffuse scattering intensity caused by the spin modulations is far stronger than that due to the lattice displacement of the localized spins. The spin modulations extend to wider space than the cluster sizes with the lattice distortion. Relations are discussed between the spin modulations and the various anomalous magnetic behaviors reported by previous authors as common properties of the Invar alloys.

    DOI CiNii

  • Lattice dynamics of cubic NaNbO3: An inelastic neutron scattering study

    Izumi Tomeno, Yorihiko Tsunoda, Kunihiko Oka, Masato Matsuura, Masakazu Nishi

    Physical Review B - Condensed Matter and Materials Physics   80 ( 10 ) 104101  2009年09月

     概要を見る

    The phonon-dispersion relations for cubic NaNbO3 have been determined along the [100], [110], and [111] directions using inelastic neutron scattering. A simultaneous softening of transverse acoustic (TA) phonon modes occurs at the zone-boundary M (0.5,0.5,0) and R (0.5,0.5,0.5) points, indicating the instabilities of in-phase and out-of-phase rotations of the oxygen octahedra about the [001] direction. These zone-boundary modes exhibit an extremely gradual softening as the temperature is lowered toward Tc1 =913K. The inelastic diffuse scattering at the M (0.5,0.5,0) point polarized along the [1 1̄ 0] direction remains up to 9 meV, whereas the inelastic diffuse scattering at the M point polarized along the [001] direction is suppressed. Polarization dependence shows that the inelastic diffuse scattering at the M and R points originates from the dynamical motion of oxygen octahedra. The transverse optic (TO) phonon modes along the [110] direction polarized with the [001] direction also soften around q= [0.15,0.15,0] and merge into the lower-energy TA phonon modes. This is basically similar to the waterfall phenomenon observed for Pb-based perovskite relaxor ferroelectrics. The extreme broad longitudinal acoustic (LA) and TA modes in NaNbO3 contribute significantly to the inelastic diffuse scattering around Bragg points. The broadening of TA and TO modes are attributed to the anharmoic lattice potential in NaNbO3. The coexistence of long-wavelength and zone-boundary phonon instabilities above Tc1 =913K is closely related to the complex sequence of phase transitions in NaNbO3. © 2009 The American Physical Society.

    DOI CiNii

  • Neutron Diffraction Study of Martensitic Transformation of Off-Stoichiometric Single-Crystal Ni2MnGa

    Kazuko Inoue, Yasuo Yamaguchi, Haruhiro Hiraka, Toetsu Shishido, Hidefumi Maeda, Yorihiko Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 3 ) 034602  2009年03月

     概要を見る

    Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiometric Heusler-type Ni2.16Mn0.78Ga1.06 single crystal (conduction electron-to-atom ratio = 7.56). The splitting of a cubic (020) peak on a reciprocal lattice c*-plane was traced with decreasing temperature from 400 to 37 K. It was found that an orthorhombic structure (a > b > c) appears slightly below the transformation temperature as a metastable transient precursor structure before the formation of a final stable tetragonal structure (a = b < c). The modes of deformation from cubic to orthorhombic are (i) simple shrinking and elongation of two cubic axes or (ii) a shuffling-like deformation along the cubic < 110 > direction on one of the cubic planes. The mode of deformation from orthorhombic to tetragonal is a shuffling-like deformation along the orthorhombic < 110 > direction on the orthorhombic c-plane. Both shuffling-like deformations originate from tilting deformations that preserve the common < 111 > direction.

    DOI

  • Neutron Diffraction Study of Martensitic Transformation of Off-Stoichiometric Single-Crystal Ni2MnGa

    Kazuko Inoue, Yasuo Yamaguchi, Haruhiro Hiraka, Toetsu Shishido, Hidefumi Maeda, Yorihiko Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 3 ) 034602  2009年03月

     概要を見る

    Neutron diffraction was applied to investigate the martensitic transformation of an off-stoichiometric Heusler-type Ni2.16Mn0.78Ga1.06 single crystal (conduction electron-to-atom ratio = 7.56). The splitting of a cubic (020) peak on a reciprocal lattice c*-plane was traced with decreasing temperature from 400 to 37 K. It was found that an orthorhombic structure (a > b > c) appears slightly below the transformation temperature as a metastable transient precursor structure before the formation of a final stable tetragonal structure (a = b < c). The modes of deformation from cubic to orthorhombic are (i) simple shrinking and elongation of two cubic axes or (ii) a shuffling-like deformation along the cubic < 110 > direction on one of the cubic planes. The mode of deformation from orthorhombic to tetragonal is a shuffling-like deformation along the orthorhombic < 110 > direction on the orthorhombic c-plane. Both shuffling-like deformations originate from tilting deformations that preserve the common < 111 > direction.

    DOI

  • Spin Correlations in a simple cubic antiferromagnet L1-2 -type Pt3Fe

    R. Matsui, Y. Tsunoda

    J. Phys. : Cond. Matt.   21   124209  2009年

  • Spin Correlations in a simple cubic antiferromagnet L1-2 -type Pt3Fe

    R. Matsui, Y. Tsunoda

    J. Phys. : Cond. Matt.   21   124209  2009年

  • Lattice dynamics of cubic NanbO3: An inelastic neutron scattering study

    I. Tomeno, Y. Tsunoda, K. Oka, M. Matsuura, M. Nishi

    Phys. Rev. B   80 ( 10 ) 104101  2009年

    DOI CiNii

  • Elastic diffuse scattering of neutrons in FeNi Invar alloys

    Y. Tsunoda, L. Hao, S. Shimomura, F. Ye, J. L. Robertson, J. Fernandez-Baca

    PHYSICAL REVIEW B   78 ( 9 ) 094105  2008年09月

     概要を見る

    Elastic diffuse scattering of neutrons was found around various Bragg-peak positions in FeNi Invar alloys. The diffuse scattering intensities depend on the temperature and Ni concentration. The intensities increase with decreasing temperature and decrease with increasing Ni concentration. The distribution of diffuse scattering intensity changes from peak to peak and is well explained by the formation of clusters with a lattice deformation consisting of a shear wave propagating along the < 1 1 0 > direction and with the < 1 - 1 0 > polarization vector. The ranges of temperature and Ni concentration, for which diffuse scattering is observed, coincide with those for which the Invar anomalies are observable. The origin of the clusters together with the lattice deformation and their role with regard to the Invar effects are discussed as well as the possibility of a precursor for the fcc-bcc martensitic transformation observed in FeNi alloys.

    DOI CiNii

  • Elastic diffuse scattering of neutrons in FeNi Invar alloys

    Y. Tsunoda, L. Hao, S. Shimomura, F. Ye, J. L. Robertson, J. Fernandez-Baca

    PHYSICAL REVIEW B   78 ( 9 ) 094105  2008年09月

     概要を見る

    Elastic diffuse scattering of neutrons was found around various Bragg-peak positions in FeNi Invar alloys. The diffuse scattering intensities depend on the temperature and Ni concentration. The intensities increase with decreasing temperature and decrease with increasing Ni concentration. The distribution of diffuse scattering intensity changes from peak to peak and is well explained by the formation of clusters with a lattice deformation consisting of a shear wave propagating along the < 1 1 0 > direction and with the < 1 - 1 0 > polarization vector. The ranges of temperature and Ni concentration, for which diffuse scattering is observed, coincide with those for which the Invar anomalies are observable. The origin of the clusters together with the lattice deformation and their role with regard to the Invar effects are discussed as well as the possibility of a precursor for the fcc-bcc martensitic transformation observed in FeNi alloys.

    DOI CiNii

  • Anomaly in the field dependence of the anisotropic magnetic susceptiblity of a single-grained α-Mn

    Hiroshi Nakano, Masahiro Mori, Yorihiko Tsunoda, Susumu Matsuo

    Journal of Magnetism and Magnetic Materials   320 ( 16 ) 2094 - 2098  2008年08月

     概要を見る

    A kink was observed near 20 kOe in the field dependence of the magnetization in a single-grained α-Mn without a magnetic hysteresis below the Neel temperature in an accurate magnetization measurement below 80 kOe. It was observed along [1 0 0], [1 1 0] and [1 1 1] crystallographic directions. The field dependence of the magnetization above 40 kOe extrapolates to positive finite magnetization at null field. The kink suggests a weak metamagnetism induced by the external magnetic field. A small but clear anisotropy was observed between the weak-field susceptibilities along [1 0 0] and [1 1 0]/[1 1 1] directions. A previously reported large susceptibility anomaly was not affirmed between 90 and 270 kOe. © 2008 Elsevier B.V. All rights reserved.

    DOI CiNii

  • Anomaly in the field dependence of the anisotropic susceptibility of a single grained alpha-Mn

    H. Nakano, M. Mori, Y. Tsunoda, S. Matsuo

    J. Mag. Mag. Mater.   320 ( 16 ) 2094 - 2098  2008年

    DOI CiNii

  • Simple cubic antiferromagnet Pt3Fe alloy under uniaxial pressure

    S. Yano, Y. Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 ) 1841 - 1843  2007年03月

     概要を見る

    Magnetism of simple cubic antiferromagnet Pt3Fe alloy was studied by neutron scattering under uniaxtial pressure. NW temperature while relative intensity of the (1)/(1)(2)/(2)0 Bragg peak at the low-temperature phase decreased under the uniaxial pressure. Actual nonincreased, collinear magnetic structure model at the low-temperature phase was proposed under the reasonable assumption. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Magnon and magnetic structure of FePt alloy

    S. Akiyama, Y. Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 ) 1844 - 1846  2007年03月

     概要を見る

    To determine the exchange coupling constants between spins, magnon dispersion relation in FePt alloy was studied by neutron inelastic scattering measurements. Data analysis based on the localized spin model led to the result that magnetic moments of Pt atoms couple with those of Fe atoms anti-parallel. Powder diffraction measurements were also performed to determine the sizes and the direction of magnetic moments of Fe and Pt atoms. The results were 1.93 and -0.49 mu(B) for Fe and Pt, respectively. The results are consistent with those of magnon dispersion relation. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Spin-glass-like behavior of MnCu alloy

    M. Yanagida, Y. Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 ) 1529 - 1531  2007年03月

     概要を見る

    Strong inelastic scattering of neutrons extends along the first Brillouin zone boundary of FCC structure on Mn73Cu27 alloy at room temperature, indicating that Mn spins fluctuate dynamically with strong spin correlations. The fluctuation is considered to be caused by geometrical spin frustration of the octahedral antiferromagnet and suppresses the magnetic LRO. At low temperature, part of spins freezes due to the randomness of atomic arrangements, resulting in spin-glass-like behavior. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Simple cubic antiferromagnet Pt3Fe alloy under uniaxial pressure

    S. Yano, Y. Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 ) 1841 - 1843  2007年03月

     概要を見る

    Magnetism of simple cubic antiferromagnet Pt3Fe alloy was studied by neutron scattering under uniaxtial pressure. NW temperature while relative intensity of the (1)/(1)(2)/(2)0 Bragg peak at the low-temperature phase decreased under the uniaxial pressure. Actual nonincreased, collinear magnetic structure model at the low-temperature phase was proposed under the reasonable assumption. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Magnon and magnetic structure of FePt alloy

    S. Akiyama, Y. Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 ) 1844 - 1846  2007年03月

     概要を見る

    To determine the exchange coupling constants between spins, magnon dispersion relation in FePt alloy was studied by neutron inelastic scattering measurements. Data analysis based on the localized spin model led to the result that magnetic moments of Pt atoms couple with those of Fe atoms anti-parallel. Powder diffraction measurements were also performed to determine the sizes and the direction of magnetic moments of Fe and Pt atoms. The results were 1.93 and -0.49 mu(B) for Fe and Pt, respectively. The results are consistent with those of magnon dispersion relation. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Spin-glass-like behavior of MnCu alloy

    M. Yanagida, Y. Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   310 ( 2 ) 1529 - 1531  2007年03月

     概要を見る

    Strong inelastic scattering of neutrons extends along the first Brillouin zone boundary of FCC structure on Mn73Cu27 alloy at room temperature, indicating that Mn spins fluctuate dynamically with strong spin correlations. The fluctuation is considered to be caused by geometrical spin frustration of the octahedral antiferromagnet and suppresses the magnetic LRO. At low temperature, part of spins freezes due to the randomness of atomic arrangements, resulting in spin-glass-like behavior. (c) 2006 Elsevier B.V. All rights reserved.

    DOI

  • Spin-flip transition of L10-type PtMn alloy single crystal studied by neutron scattering

    H. Hama, R. Motomura, T. Shnozaki, Y. Tsunoda

    J Phys. : Cond. Matt.   19   176228  2007年

  • Lattice symmetry of the spiral spin-density wave state in Gamma-Fe precipitates in Cu

    Y. Tsunoda, H. Nogami, M. Takasaka

    Phys. Rev. B   76 ( 5 ) 054419  2007年

    DOI CiNii

  • Spinel-type frustrated spin system MgCr2O4

    H. Suzuki, Y. Tsunoda

    J. Phys. Chem. Solids   68   2060 - 2063  2007年

    DOI

  • Spin-flip transition of L10-type PtMn alloy single crystal studied by neutron scattering

    H. Hama, R. Motomura, T. Shnozaki, Y. Tsunoda

    J Phys. : Cond. Matt.   19   176228  2007年

  • Lattice symmetry of the spiral spin-density wave state in Gamma-Fe precipitates in Cu

    Y. Tsunoda, H. Nogami, M. Takasaka

    Phys. Rev. B   76 ( 5 ) 054419  2007年

    DOI CiNii

  • Spinel-type frustrated spin system MgCr2O4

    H. Suzuki, Y. Tsunoda

    J. Phys. Chem. Solids   68   2060 - 2063  2007年

    DOI

  • Lattice dynamics of tetragonal PbTiO3

    Tomeno, I, Y Ishii, Y Tsunoda, K Oka

    PHYSICAL REVIEW B   73 ( 6 ) 064116  2006年02月

     概要を見る

    The phonon dispersion relations for tetragonal PbTiO3 have been determined along the [100], [110], and [001] directions at room temperature by inelastic neutron scattering. The zone-boundary TA phonon energies for PbTiO3 are considerably lower than those for BaTiO3 and SrTiO3, indicating the dominant role of Pb atoms in TA phonons. The zone-center TO-A(1) phonon energy is higher than the zone-center TO-E phonon energy. A preliminary high-temperature experiment has revealed the gradual softening of the TO-A(1) phonons and the stability of TO-E phonons up to 643 K (0.84 T-c). The TO-A(1) phonons have an extremely broad linewidth, in marked contrast to the well-defined TO-E phonons. The TO phonons at the zone-boundary M point indicate that the energy for the rotational mode of the oxygen octahedra is approximately half of that for the distortion of the octahedra along the c axis. The X-point TO phonon energies for PbTiO3 are much higher than those for Pb(Zn1/3Nb2/3)O-3, suggesting that the B-site atoms in ABO(3) contribute largely to the TO phonons in Pb-based perovskites. Present phonon dispersion relations are generally in agreement with the first-principles calculations for the zone-center and zone-boundary phonon energies.

    DOI CiNii

  • Lattice dynamics of tetragonal PbTiO3

    Tomeno, I, Y Ishii, Y Tsunoda, K Oka

    PHYSICAL REVIEW B   73 ( 6 ) 064116  2006年02月

     概要を見る

    The phonon dispersion relations for tetragonal PbTiO3 have been determined along the [100], [110], and [001] directions at room temperature by inelastic neutron scattering. The zone-boundary TA phonon energies for PbTiO3 are considerably lower than those for BaTiO3 and SrTiO3, indicating the dominant role of Pb atoms in TA phonons. The zone-center TO-A(1) phonon energy is higher than the zone-center TO-E phonon energy. A preliminary high-temperature experiment has revealed the gradual softening of the TO-A(1) phonons and the stability of TO-E phonons up to 643 K (0.84 T-c). The TO-A(1) phonons have an extremely broad linewidth, in marked contrast to the well-defined TO-E phonons. The TO phonons at the zone-boundary M point indicate that the energy for the rotational mode of the oxygen octahedra is approximately half of that for the distortion of the octahedra along the c axis. The X-point TO phonon energies for PbTiO3 are much higher than those for Pb(Zn1/3Nb2/3)O-3, suggesting that the B-site atoms in ABO(3) contribute largely to the TO phonons in Pb-based perovskites. Present phonon dispersion relations are generally in agreement with the first-principles calculations for the zone-center and zone-boundary phonon energies.

    DOI CiNii

  • Symmetry breaking in a frustrated Heisenberg spin system ZnCr3O4 - 1(Magnetic Measurement)

    I. Kagomiya, H. Suzuki, E. Kita, Y. Tsunoda, K. Kohn, K. Siratori

    J. Phys. Soc. Japan   75   064709  2006年

    DOI

  • Symmetry breaking in a frustrated Heisenberg spin system ZnCr3O4 - 1(Magnetic Measurement)

    I. Kagomiya, H. Suzuki, E. Kita, Y. Tsunoda, K. Kohn, K. Siratori

    J. Phys. Soc. Japan   75   064709  2006年

    DOI

  • Phonon density of states of pseudomorphic fcc-Fe film

    T Tanaka, A Tajima, R Moriizumi, C Oshima, Y Tsunoda, M Seto, S Kitao, T Mitsui

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 6 ) 1762 - 1765  2005年06月

     概要を見る

    The phonon density of states of a pseudomorphic fcc-Fe film with similar to 3 monolayers has been investigated by nuclear resonant inelastic scattering. The fcc-Fe layers are intercalated into an interface between monolayer hexagonal boron nitride and a Ni(111) substrate with a commensurate relation. The in-plane nearest-neighbor distance of the fcc-Fe film is shorter than that of uncompressed fcc-Fe precipitates in Cu by -1.8%. The compression increases the mean force constant of the fcc-Fe film, which is higher than that of uncompressed fcc-Fe precipitates by 5.8%.

    DOI CiNii

  • Phonon density of states of pseudomorphic fcc-Fe film

    T Tanaka, A Tajima, R Moriizumi, C Oshima, Y Tsunoda, M Seto, S Kitao, T Mitsui

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 6 ) 1762 - 1765  2005年06月

     概要を見る

    The phonon density of states of a pseudomorphic fcc-Fe film with similar to 3 monolayers has been investigated by nuclear resonant inelastic scattering. The fcc-Fe layers are intercalated into an interface between monolayer hexagonal boron nitride and a Ni(111) substrate with a commensurate relation. The in-plane nearest-neighbor distance of the fcc-Fe film is shorter than that of uncompressed fcc-Fe precipitates in Cu by -1.8%. The compression increases the mean force constant of the fcc-Fe film, which is higher than that of uncompressed fcc-Fe precipitates by 5.8%.

    DOI CiNii

  • The Particle Size Effect of the Spin Density Wave in Cubic γーFe Precipitates in Cu

    T. Naono, Y. Tsunoda

    J. Phys. Cond. Matter   16 ( 43 ) 7723 - 7732  2004年11月

    DOI CiNii

  • The particle size effect of the spin-density wave in cubic gamma-Fe precipitates in Cu

    T Naono, Y Tsunoda

    JOURNAL OF PHYSICS-CONDENSED MATTER   16 ( 43 ) 7723 - 7732  2004年11月

     概要を見る

    It is common knowledge that the magnetic structure of fcc Fe (gamma-Fe) can be described by means of an incommensurate spin-density wave (SDW). Previous experimental data, however, were mostly obtained for gamma-FeCo alloy precipitates in Cu in order to avoid the complexity of the structural phase transition. Since Fe is a fundamental element, reliable data on the SDW state for pure gamma-Fe are highly desired. We present here neutron scattering data for the SDW in pure gamma-Fe precipitates in Cu and discuss the particle size effect of the SDW.

    DOI CiNii

  • Magnetic properties of ZnFe2O4 as a 3-D geometrical spin frustration system

    T Usa, K Kamazawa, H Sekiya, S Nakamura, Y Tsunoda, K Kohn, M Tanaka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 10 ) 2834 - 2840  2004年10月

     概要を見る

    Magnetic properties of ZnFe2O4 were studied for various specimens prepared by different thermal and artificial treatments using neutron scattering, Mossbauer spectroscopy and DC and AC susceptibilities. We found a strong correlation between the magnetic Bragg peak intensity and the Mossbauer absorption line-width. Comparing with the susceptibility data, it is discussed what are the intrinsic magnetic properties of ZnFe2O4 as a typical 3-D geometrical spin frustration system.

    DOI CiNii

  • Magnetic properties of ZnFe2O4 as a 3-D geometrical spin frustration system

    T Usa, K Kamazawa, H Sekiya, S Nakamura, Y Tsunoda, K Kohn, M Tanaka

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   73 ( 10 ) 2834 - 2840  2004年10月

     概要を見る

    Magnetic properties of ZnFe2O4 were studied for various specimens prepared by different thermal and artificial treatments using neutron scattering, Mossbauer spectroscopy and DC and AC susceptibilities. We found a strong correlation between the magnetic Bragg peak intensity and the Mossbauer absorption line-width. Comparing with the susceptibility data, it is discussed what are the intrinsic magnetic properties of ZnFe2O4 as a typical 3-D geometrical spin frustration system.

    DOI CiNii

  • Dissociation of spin objects in geometrically frustrated CdFe <inf>2</inf>O<inf>4</inf>

    K. Kamazawa, S. Park, S. H. Lee, T. J. Sato, Y. Tsunoda

    Physical Review B - Condensed Matter and Materials Physics   70 ( 2 ) 1 - 5  2004年07月

     概要を見る

    Using inelastic neutron scattering, we measured the diffuse scattering pattern of the geometrically frustrated 110CdFe2O 4. The observed pattern resembles that of ZnCr2O 4, indicative of strong nearest-neighbor antiferromagnetic correlations in contrast to the ferromagnetic nearest neighbor interactions of the isomorphic ZnFe2O4. This result demonstrates that the subtle 90° Fe3+-O-Fe3+ interaction changes its nature by chemical pressure. Meanwhile, the temperature dependence of the diffuse scattering shows hexagonal spin objects decay very gradually with increasing temperature and can be seen even at temperature as high as five times Curie-Weiss temperature. At low temperatures, spin freezing with only short-range correlations is observed associated with 13 K susceptibility anomaly. No long-range order is found down to 0.1 K with applied field of up to 9 T.

    DOI

  • Dissociation of spin objects in geometrically frustrated CdFe <inf>2</inf>O<inf>4</inf>

    K. Kamazawa, S. Park, S. H. Lee, T. J. Sato, Y. Tsunoda

    Physical Review B - Condensed Matter and Materials Physics   70 ( 2 ) 1 - 5  2004年07月

     概要を見る

    Using inelastic neutron scattering, we measured the diffuse scattering pattern of the geometrically frustrated 110CdFe2O 4. The observed pattern resembles that of ZnCr2O 4, indicative of strong nearest-neighbor antiferromagnetic correlations in contrast to the ferromagnetic nearest neighbor interactions of the isomorphic ZnFe2O4. This result demonstrates that the subtle 90° Fe3+-O-Fe3+ interaction changes its nature by chemical pressure. Meanwhile, the temperature dependence of the diffuse scattering shows hexagonal spin objects decay very gradually with increasing temperature and can be seen even at temperature as high as five times Curie-Weiss temperature. At low temperatures, spin freezing with only short-range correlations is observed associated with 13 K susceptibility anomaly. No long-range order is found down to 0.1 K with applied field of up to 9 T.

    DOI

  • Temperature variation of the tetragonality in ordered PtFe alloy

    Y Tsunoda, H Kobayashi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   776 - 777  2004年05月

     概要を見る

    Tetragonal lattice distortion of the PtFe alloy was studied by neutron diffraction as a function of temperature. The tetragonality (1 - c/a) increases with increasing temperature up to the Curie temperature (T-C = 750 K). Data analysis based on the hard sphere model in the (1 1 1) plane leads to the shrink of the atomic volume of Fe with increasing temperature. The invar-like effect at high temperature would exert a significant influence on the magnetic anisotropy energy of this system. (C) 2004 Elsevier B.V. All rights reserved.

    DOI

  • Partial spin frustration system in the ordered Mn3Pt alloy

    T Ikeda, Y Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   482 - 484  2004年05月

     概要を見る

    Mn3Pt alloy has a special magnetic structure, which is considered that one third of Mn atoms have no magnetic moment. We found that the lattice slightly distorts to a tetragonal structure and our neutron scattering data in the F-phase show inelastic diffuse scattering located along the first Brillouin zone boundary of the FCC-structure, indicating that the one third of Mn spins fluctuate dynamically with strong correlations. The Mn3Pt alloy has a partial spin frustration. Coexistence of static collinear spin structure and dynamical spins in the F-phase is a characteristic of the ordered Mn3Pt alloy. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

  • Temperature variation of the tetragonality in ordered PtFe alloy

    Y Tsunoda, H Kobayashi

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   776 - 777  2004年05月

     概要を見る

    Tetragonal lattice distortion of the PtFe alloy was studied by neutron diffraction as a function of temperature. The tetragonality (1 - c/a) increases with increasing temperature up to the Curie temperature (T-C = 750 K). Data analysis based on the hard sphere model in the (1 1 1) plane leads to the shrink of the atomic volume of Fe with increasing temperature. The invar-like effect at high temperature would exert a significant influence on the magnetic anisotropy energy of this system. (C) 2004 Elsevier B.V. All rights reserved.

    DOI

  • Partial spin frustration system in the ordered Mn3Pt alloy

    T Ikeda, Y Tsunoda

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   482 - 484  2004年05月

     概要を見る

    Mn3Pt alloy has a special magnetic structure, which is considered that one third of Mn atoms have no magnetic moment. We found that the lattice slightly distorts to a tetragonal structure and our neutron scattering data in the F-phase show inelastic diffuse scattering located along the first Brillouin zone boundary of the FCC-structure, indicating that the one third of Mn spins fluctuate dynamically with strong correlations. The Mn3Pt alloy has a partial spin frustration. Coexistence of static collinear spin structure and dynamical spins in the F-phase is a characteristic of the ordered Mn3Pt alloy. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

  • Magnetic Field Effect on the Diffuse Scattering of a spin-frustrated spinel ferrite ZnFe2O4

    K. Kamazawa, S. Katano, Y. Tsunoda

    Physica B   345   3305 - 3306  2004年

    DOI

  • 連載 入門講座 「3軸法入門」(理論編)

    角田頼彦

    中性子科学会会誌 「波紋」   12~14  2004年

  • Magnetic Field Effect on the Diffuse Scattering of a spin-frustrated spinel ferrite ZnFe2O4

    K. Kamazawa, S. Katano, Y. Tsunoda

    Physica B   345   3305 - 3306  2004年

    DOI

  • Magnetism of Pt0.67Fe0.33 alloy

    Y Higashiyama, Y Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 12 ) 3305 - 3306  2003年12月

    DOI

  • Magnetism of Pt0.67Fe0.33 alloy

    Y Higashiyama, Y Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 12 ) 3305 - 3306  2003年12月

    DOI

  • Spin fluctuations in an octahedral antiferromagnet Mn3Pt alloy

    T Ikeda, Y Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 10 ) 2614 - 2621  2003年10月

     概要を見る

    A new spin frustration system with an octahedral configuration of magnetic atoms was found. In neutron scattering measurements for an ordered Mn3Pt alloy, inelastic diffuse scattering intensity distributes along the first Brillouin zone-boundary of the fee structure in the paramagnetic and the F-phases. Within the calculations based on a RPA, the experimental data in the paramagnetic phase are reproduced using antiferromagnetic couplings between the spins up to the third-neighbor exchange interactions. In the F-phase below the Neel temperature, a part of the Mn spins still fluctuates at the special site. The existence of the F-phase is a characteristic of the octahedral spin frustration system. The effects of the chemical disorder on the spin frustration are also studied using a specimen with a small atomic LRO parameter.

    DOI CiNii

  • Spin fluctuations in an octahedral antiferromagnet Mn3Pt alloy

    T Ikeda, Y Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 10 ) 2614 - 2621  2003年10月

     概要を見る

    A new spin frustration system with an octahedral configuration of magnetic atoms was found. In neutron scattering measurements for an ordered Mn3Pt alloy, inelastic diffuse scattering intensity distributes along the first Brillouin zone-boundary of the fee structure in the paramagnetic and the F-phases. Within the calculations based on a RPA, the experimental data in the paramagnetic phase are reproduced using antiferromagnetic couplings between the spins up to the third-neighbor exchange interactions. In the F-phase below the Neel temperature, a part of the Mn spins still fluctuates at the special site. The existence of the F-phase is a characteristic of the octahedral spin frustration system. The effects of the chemical disorder on the spin frustration are also studied using a specimen with a small atomic LRO parameter.

    DOI CiNii

  • Crossover of spin correlations in Pt100-XFeX (16 &lt;= X &lt;= 25) alloys

    Y Tsunoda, D Tsuchiya, Y Higashiyama

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 3 ) 713 - 717  2003年03月

     概要を見る

    Magnetic structures of Pt100-XFeX (X = 16, 18, 24 and 25) alloys were studied by means of neutron elastic and inelastic scattering. Non-collinear antiferromagnetic structure is experimentally verified for the ground state of the stoichiometric alloy Pt3Fe. The antiferromagnetic phase transition below T-N in Pt3Fe alloy is considered to be one of the crossover points of the antiferromagnetic spin correlations which show successive change towards the original point of the reciprocal lattice with increasing Fe concentration in the wide concentration range of the Pt-Fe system.

    DOI CiNii

  • Crossover of spin correlations in Pt100-XFeX (16 &lt;= X &lt;= 25) alloys

    Y Tsunoda, D Tsuchiya, Y Higashiyama

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   72 ( 3 ) 713 - 717  2003年03月

     概要を見る

    Magnetic structures of Pt100-XFeX (X = 16, 18, 24 and 25) alloys were studied by means of neutron elastic and inelastic scattering. Non-collinear antiferromagnetic structure is experimentally verified for the ground state of the stoichiometric alloy Pt3Fe. The antiferromagnetic phase transition below T-N in Pt3Fe alloy is considered to be one of the crossover points of the antiferromagnetic spin correlations which show successive change towards the original point of the reciprocal lattice with increasing Fe concentration in the wide concentration range of the Pt-Fe system.

    DOI CiNii

  • Magnetic Neutron Scattering Measurements on a single crystal of frustrated ZnFe2O4

    K. Kamazawa, Y. Tsunoda, H. Kadowaki, K. Kohn

    Phys. Rev. B   68 24412   1 - 9  2003年

  • Magnetic Neutron Scattering Measurements on a single crystal of frustrated ZnFe2O4

    K. Kamazawa, Y. Tsunoda, H. Kadowaki, K. Kohn

    Phys. Rev. B   68 24412   1 - 9  2003年

  • Atomic concentration wave in Pt-Ti and Pd-Ti alloys

    Y Kurimoto, Y Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   71 ( 12 ) 2827 - 2828  2002年12月

     概要を見る

    The atomic short range order of Pd-Ti and Pt-Ti alloys with a Ti concentration of about 10 at.% was studied by neutron diffraction. Temperature-independent diffuse satellite peaks were observed at incommensurate positions on the [100] axis. Due to the various properties of the diffuse satellite peaks, a concentration wave of constituent atoms appeared as a reflection of the special shape of the Fermi surfaces of the alloys. Its relationship to the Pt8Ti superlattice structure is discussed.

    DOI CiNii

  • Phonon Density States of γ-Fe Precipitates in Cu

    Y. Tsunoda, Y. Kurimoto, M. Seto, S. Kitao, Y. Yoda

    Phys. Rev. B   66 ( 21 ) 1 - 5  2002年12月

    DOI

  • Atomic concentration wave in Pt-Ti and Pd-Ti alloys

    Y Kurimoto, Y Tsunoda

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   71 ( 12 ) 2827 - 2828  2002年12月

     概要を見る

    The atomic short range order of Pd-Ti and Pt-Ti alloys with a Ti concentration of about 10 at.% was studied by neutron diffraction. Temperature-independent diffuse satellite peaks were observed at incommensurate positions on the [100] axis. Due to the various properties of the diffuse satellite peaks, a concentration wave of constituent atoms appeared as a reflection of the special shape of the Fermi surfaces of the alloys. Its relationship to the Pt8Ti superlattice structure is discussed.

    DOI CiNii

  • Phonon density of states of gamma-Fe precipitates in Cu

    Y Tsunoda, Y Kurimoto, M Seto, S Kitao, Y Yoda

    PHYSICAL REVIEW B   66 ( 21 ) 1 - 5  2002年12月

     概要を見る

    The phonon density of states of gamma-Fe precipitates in a Cu matrix were studied as a function of particle size by using nuclear resonant inelastic scattering of synchrotron radiation. The host metal affects the phonon density of states of the precipitates up to 30 nm in diameter. Larger precipitates are free from the influence of the host metal and show rather similar phonon density of states to those of fcc-Fe alloy bulk specimens such as stainless steel (310ss) and Fe70Ni30 at room temperature although gamma-Fe is unstable at room temperature under an atmospheric condition. Careful observation, however, yields characteristics of gamma-Fe precipitates in the phonon density of states.

    DOI

  • Inter-spin Interaction in ZnFe2O4

    Y. Yamada, K. Kamazawa, Y. Tsunoda

    Phys. Rev. B   66   64401 - 64407  2002年

  • Inter-spin Interaction in ZnFe2O4

    Y. Yamada, K. Kamazawa, Y. Tsunoda

    Phys. Rev. B   66   64401 - 64407  2002年

  • Mössbauer Study on a Triangular Lattice Antiferromagnet LuFeCoO4

    Takahiro Sunaga, Midori Tanaka, Nobuhiko Sakai, Yorihiko Tsunoda

    Journal of the Physical Society of Japan   70 ( 12 ) 3713 - 3718  2001年12月

     概要を見る

    Mössbauer spectra of a single crystal of LuFeCoO4 are studied in the temperature range between 4.2 K and 70 K. The Mössbauer spectra are separated into two components. We propose a model that one of three spins in a spin plane is parallel to the c-axis and other two orient to 120 to the c-axis. This model explains the experimental data satisfactory. It is concluded that the spins parallel to the c-axis are more stable than the other when temperature is increased. The Ising like character observed in susceptibility measurements can be explained by this spin arrangement in the spin planes.

    DOI CiNii

  • 中性子でみた遍歴電子スピングラスの構造と磁性

    角田頼彦

    日本物理学会    2001年

  • Spin Modulation Wave in Giant Magnetic Moment Systems PdCo and PtCo Alloys

    K. Fushimi, Y. Tsunoda

    J. Phys. Soc. Japan   70 ( 5 ) 1364 - 1368  2001年

    DOI CiNii

  • Spin Correlations in Mn3Pt

    T. Ikeda, Y. Tsunoda

    J. Phys. Soc. Japan   70巻 Suppl.A   130 - 132  2001年

  • Neutron Scattering Studies of PdMn and PtMn Alloys

    A. Harigae, T. Sunaga, Y. Tsunoda

    J. Phys. Soc. Japan   70巻 Suppl.A   133 - 135  2001年

  • Lattice Dynamics of Disordered Perovskite Pb(Zn1/3Nb2/3)O3

    I. Tomeno, S. Shimanuki, Y. Tsunoda, Y. Ishii

    J. Phys. Soc. Japan   70 ( 6 ) 1444 - 1447  2001年

    DOI

  • Charge and Spin ordering in LiMn2O4

    I. Tomeno, Y. Kasuya, 案dY. Tsunoda

    Phys. Rev. B   64巻   94422  2001年

  • Mossbauer Study on a Trianguler Lattice Antiferromagnet LuFeCoO4

    T. Sunaga, M. Tanaka, N. Sakai, Y. Tsunoda

    J. Phys. Soc. Japan   70 ( 12 ) 3713 - 3718  2001年

    DOI CiNii

  • Spin Modulation Wave in Giant Magnetic Moment Systems PdCo and PtCo Alloys

    K. Fushimi, Y. Tsunoda

    J. Phys. Soc. Japan   70 ( 5 ) 1364 - 1368  2001年

    DOI CiNii

  • Spin Correlations in Mn3Pt

    T. Ikeda, Y. Tsunoda

    J. Phys. Soc. Japan   70巻 Suppl.A   130 - 132  2001年

  • Neutron Scattering Studies of PdMn and PtMn Alloys

    A. Harigae, T. Sunaga, Y. Tsunoda

    J. Phys. Soc. Japan   70巻 Suppl.A   133 - 135  2001年

  • Lattice Dynamics of Disordered Perovskite Pb(Zn1/3Nb2/3)O3

    I. Tomeno, S. Shimanuki, Y. Tsunoda, Y. Ishii

    J. Phys. Soc. Japan   70 ( 6 ) 1444 - 1447  2001年

    DOI

  • Charge and Spin ordering in LiMn2O4

    I. Tomeno, Y. Kasuya, 案dY. Tsunoda

    Phys. Rev. B   64巻   94422  2001年

  • Atomic short-range order and magnetism in Pt1-xCrx alloys

    Y. Tsunoda, M. Hirano, J. L. Robertson

    Physical Review B - Condensed Matter and Materials Physics   62 ( 9 ) 5570 - 5575  2000年09月

     概要を見る

    Atomic short-range order and magnetism in Pt1-xCrx alloys with x=0.07, 0.10, 0.13, and 0.16 were studied by means of neutron scattering and susceptibility measurements. The latter showed a spin-glass-type anomaly at low temperature for x=0.13 and 0.16, but a monotonic increase towards the lowest temperature for x =0.07 and 0.10. In neutron scattering, broad satellite peaks with asymmetric intensities were observed for all specimens along the [1 0 0] direction, even at room temperature. These peaks are well explained as a concentration wave of constituent atoms accompanied with a periodic lattice deformation. Magnetic diffuse scattering was observed for the specimens with x=0.13 and 0.16. The origin of the spin-glass-like behavior in these alloys is ascribed to the dynamics and freezing of spin-density-wave cluster fluctuations, similar to the case of CuMn spin-glass alloys. A breakdown of the Kondo singlet state was studied for an x= 0.10 nonmagnetic alloy using neutron scattering under a magnetic field of 6 T.

    DOI CiNii

  • Atomic short-range order and magnetism in Pt1-xCrx alloys

    Y. Tsunoda, M. Hirano, J. L. Robertson

    Physical Review B - Condensed Matter and Materials Physics   62 ( 9 ) 5570 - 5575  2000年09月

     概要を見る

    Atomic short-range order and magnetism in Pt1-xCrx alloys with x=0.07, 0.10, 0.13, and 0.16 were studied by means of neutron scattering and susceptibility measurements. The latter showed a spin-glass-type anomaly at low temperature for x=0.13 and 0.16, but a monotonic increase towards the lowest temperature for x =0.07 and 0.10. In neutron scattering, broad satellite peaks with asymmetric intensities were observed for all specimens along the [1 0 0] direction, even at room temperature. These peaks are well explained as a concentration wave of constituent atoms accompanied with a periodic lattice deformation. Magnetic diffuse scattering was observed for the specimens with x=0.13 and 0.16. The origin of the spin-glass-like behavior in these alloys is ascribed to the dynamics and freezing of spin-density-wave cluster fluctuations, similar to the case of CuMn spin-glass alloys. A breakdown of the Kondo singlet state was studied for an x= 0.10 nonmagnetic alloy using neutron scattering under a magnetic field of 6 T.

    DOI CiNii

  • Atomic concentration waves in Pt-V and Pd-V alloys

    A Murakami, Y Tsunoda

    PHYSICAL REVIEW B   61 ( 9 ) 5998 - 6002  2000年03月

     概要を見る

    Pt-V alloys with V concentrations of 7, 10, 13, and 19 at.% were studied by neutron scattering. Although an equilibrium atomic long-range order has not been reported in these concentration ranges, we observed diffuse satellite peaks around the 1+/-delta,0,0 positions at room temperature. These satellite peak positions depend on the V concentration and are incommensurate with the lattice periodicity. The diffuse satellite peaks can be explained by an atomic concentration wave, in which the impurity atoms are coupled through oscillating screening charges. Thus, the concentration wave reflects the shape of the Fermi surfaces in the Pt alloys. In order to confirm the Fermi surface effect, Pd-V alloys with V concentrations of 10, 11.5, and 13 at.% were also studied because the Fermi surfaces of Pd are very similar to those of Pt. Diffuse satellite peaks around the 100 reciprocal lattice point were again observed at room temperature in the Pd-V alloys, supporting the idea that these concentration waves are reflections of the special shape of Pt and Pd Fermi surfaces.

    DOI

  • Atomic concentration waves in Pt-V and Pd-V alloys

    A Murakami, Y Tsunoda

    PHYSICAL REVIEW B   61 ( 9 ) 5998 - 6002  2000年03月

     概要を見る

    Pt-V alloys with V concentrations of 7, 10, 13, and 19 at.% were studied by neutron scattering. Although an equilibrium atomic long-range order has not been reported in these concentration ranges, we observed diffuse satellite peaks around the 1+/-delta,0,0 positions at room temperature. These satellite peak positions depend on the V concentration and are incommensurate with the lattice periodicity. The diffuse satellite peaks can be explained by an atomic concentration wave, in which the impurity atoms are coupled through oscillating screening charges. Thus, the concentration wave reflects the shape of the Fermi surfaces in the Pt alloys. In order to confirm the Fermi surface effect, Pd-V alloys with V concentrations of 10, 11.5, and 13 at.% were also studied because the Fermi surfaces of Pd are very similar to those of Pt. Diffuse satellite peaks around the 100 reciprocal lattice point were again observed at room temperature in the Pd-V alloys, supporting the idea that these concentration waves are reflections of the special shape of Pt and Pd Fermi surfaces.

    DOI

  • Neel Temp. of a-Mn Alloys with Nonmag. Impurities

    Y. Nakai, Y. Tsunoda

    J.Phys.Soc.Japan   69 ( 1 ) 292 - 293  2000年

    DOI

  • 丸善実験物理学講座「磁気測定1」

    丸善株式会社     125 - 185  2000年

  • SDW clusters in "Ferromagnetic" Pd97.5Mn2.5Alloy

    Y. Tsunoda, A. Harigae, J.L. Robertson, M.L. Crow

    Phys. Rev. B   62 ( 14 ) 9511 - 9516  2000年

    DOI

  • 遷移金属合金に於ける短距離秩序とフェルミ面

    角田頼彦

    日本結晶学会誌   42 ( 5 ) 413 - 419  2000年

     概要を見る

    Due to a special shape of Fermi surfaces in Pd and Pt metals, charge and magnetic impurity potentials induce the oscillatory shielding with large amplitude and extending to long distance along the [100] direction. As a result, Pd-M and Pt-M (M = Ti, V, Cr, Mn, Fe and Co) alloys show short range order of different types, but with the same symmetry. These are an atomic concentration wave for non-magnetic alloys (M = Ti, V, Cr), a spin-density-wave for spin-glass alloys (M = Cr, Mn) and a transverse spin modulation wave for ferromagnetic alloys (M = Fe, Co) .

    DOI CiNii

  • SDW clusters in "Ferromagnetic" Pd97.5Mn2.5Alloy

    Y. Tsunoda, A. Harigae, J.L. Robertson, M.L. Crow

    Phys. Rev. B   62 ( 14 ) 9511 - 9516  2000年

    DOI

  • Atomic Concentration Wave in PtV and PdV Alloys

    A. Murakami, Y. Tsunoda

    Phys. Rev. B   61   5998 - 6002  2000年

    DOI

  • Symmetry breaking in a frustrated Heisenberg spin system ZnCr3O4 - 2 (Neutron Scatt)

    Y. Tsunoda, H. Suzuki, S. Katano, K. Siratori, E. Kita, K. Kohn

    J. Phys. Soc. Japan   75   064710

    DOI

  • Symmetry breaking in a frustrated Heisenberg spin system ZnCr3O4 - 2 (Neutron Scatt)

    Y. Tsunoda, H. Suzuki, S. Katano, K. Siratori, E. Kita, K. Kohn

    J. Phys. Soc. Japan   75   064710

    DOI

▼全件表示

 

特別研究期間制度(学内資金)

  • 中性子散乱によるFeNiインバー合金の磁気構造の研究

    2007年10月
    -
    2008年03月

    アメリカ   オークリッジ国立研究所

特定課題制度(学内資金)

  • 強磁性と反強磁性が競合する系の磁性

    2003年  

     概要を見る

     遷移金属の磁性はd電子数とフェルミ面の形状という、異なる2つの要因に支配されている。この2つが異なる性質を安定化しようとするとき、系は複雑な磁気的振る舞いを示すであろう。PtやPdと3d遷移金属の合金はこのような系と考えられる。例えば、FeやMnとの合金では電子数では強磁性、フェルミ面からは反強磁性になろうとするため、FeやMnの濃度や原子秩序の変化によって複雑に磁性が変化する。PtFeやPtMn合金はその強い磁気異方性と高い転移温度から超高密度磁気記録媒体やGMR素子の材料として注目を浴びているが、その微視的な基礎研究は1960年代からほとんど進展がない。本研究はこれらの系の磁性を、「強磁性と反強磁性スピン相関が競合する系」という新しい視点に立ち、最新の実験技術を駆使して研究しなおし、これらの系の磁性の基礎を解明し、磁気応用材の開発に寄与することを目的としている。 これまでの研究成果1)PdFeやPtFe無秩序合金はこれまで巨大磁気モーメント系として有名で、単純な強磁性体と考えられていた。しかし中性子散乱で[100]軸上に  磁気衛星反射が観測され反強磁性のスピン相関が共存していることが判明した。(論文1、2)2)Pt3Fe規則合金は反強磁性ー反強磁性相転移を起こすが、その原因が、あるスピン波のモードが凍結して起こることを見つけた。(論文3)3)Pt67Fe33合金の磁性は高温での強磁性相から低温の反強磁性に相転移すると考えられていたが、単結晶の中性子散乱の実験から強磁性領域  と反強磁性領域が混在した不均一モデルで説明できることが判明した。(論文4)4)Pt50Fe50規則合金では低温からキュリー温度まで昇温するにつれて格子歪が増大し、インバー効果で説明出来る。Fe3Pt合金では良く知られ  た現象であるがPt50Fe50ではそのような報告はない。(論文5)5)Mn3Pt規則合金は1/3のMn原子が磁気モーメントを持たない不思議な磁気構造を示すことで興味深い系であるが、中性子非弾性散乱の結果か  ら、この系は正8面体のコーナーに配置したスピンの反強磁性結合に由来する3次元スピンフラストレーション系であることが判明した。正  8面体配置のスピンフラストレーションはこの研究が始めてである。また、不思議な磁気構造は、このフラストレーションを解消するように  1/3のスピンを動かすことで時間平均を0にし、正3角配置を消滅させた、部分的フラストレーションであることが判明した。(論文6)6)その他、Pt50Mn50合金でも興味深い結果を得ている。(論文作成中)

  • 合金の遮蔽効果とフェルミ面

    2000年  

     概要を見る

     金属母体に不純物が導入されると、金属では自由に運動出来る伝導電子が存在するので不純物原子核の余分な電荷を遮蔽するように電子が集まる。このとき、遮蔽電子の分布は一様な変化をせず、電荷分布が母体金属のフェルミ面の形状を反映した振動を示すことが知られている。(Friedel Oscillation)特に、フェルミ面の形状が平行な平面を形成している場合は、この振動の振幅は非常に大きく、しかも長距離に及ぶ。また、不純物が磁性金属である場合には、不純物スピンを伝導電子のスピンが遮蔽する。この場合もフェルミ面の形状が反映される。(sd相互作用)我々はPtやPdに3d遷移金属を不純物として導入した際、不純物の種類によって系統的に変化する3種類の異なるタイプの振動する遮蔽が起こり、遮蔽電子の相互作用を通して不純物間に相互作用が働き、3種類の異なった、結晶格子の周期とは非整合な波長を持つ変調波の短距離秩序が形成されることを見出した。即ちTi、V、Cr合金では、構成原子の濃度が波状に振動する濃度密度波、Cr、Mn合金ではスピンの方向が振動するスピン密度波、Fe、Co合金では強磁性スピンの向きが変調した強磁性スピン変調波である。これらの波はPtやPdのフェルミ面の形状を反映して、どれも[1 0 0]結晶軸方向に伝播する同じ対称性をもつ波で、不純物濃度によって波長が連続的に変化する。この波はいずれも短距離秩序であることが特徴である。このようにして生じた短距離秩序は、これらの系の物性に多大な影響をあたえており、いくつかのスピン密度波系ではスピングラスの原因になっているし、強磁性体でも磁化が飽和しにくいのはこの変調波のためである。これまで不純物の遮蔽が原因で形成された、合金中にフェルミ面の形状を反映した非整合の波はCuMn合金のスピン密度波が知られていたが、今回のPt、Pd系合金のように不純物ポテンシャルを変化させたときに系統的に変化する変調波の発見は始めてである。

  • 中性子非弾性散乱による合金のスピノーダル分解の研究

    1996年  

     概要を見る

     合金のスピノーダル分解では、その初期に構成原子の濃度が空間的に長周期の波を形成する。 この時、構成原子の質量に大きな差があると、試料中に質量の密度の波が生じることになる。 この様な質量密度波を持つ系を伝播する格子振動の波は、その波長が質量密度波の波長に比べて長い場合と短い場合で様子が異なるであろう。従って格子振動の分散関係に異常が期待される。 この異常を詳しく解析することで、格子振動の分散関係からスピノーダル分解についての新しい情報を得られる可能性がある。 このような目的で、典型的なスピノーダル系であるAlZn合金の格子振動の分散関係を中性子非弾性散乱を用いて測定した。 Al85Zn15合金(質量比 2.0)は室温でスピノーダル分解を起こし、周期 約 35Aの濃度波が生じる事が知られている。従って、室温の時効時間によって質量密度波の振幅が変化し、分散関係に時間に依存する異常が期待される。 中性子散乱の結果は、波長 50 A付近に分散関係に不連続を示す異常が観測され、この付近でエネルギーギャップが生じている事を示している。またこの異常が時間とともに顕著になっていることから質量密度波によるものであると考えられる。 一方、質量密度波を持つ一次元系でコンピューターシミュレイションをおこなったところ、質量密度波の波数ベクトルの半分の位置に、エネルギーギャップが生じる事がわかった。この値は実験で得られた位置と少しずれている。 これは計算では原子間結合力(ばね定数)を一定にして計算しているのにたいし、現実の系ではこれが異なるためであると考えられる。 現在のところ、観測されている異常はやや小さく、このデータからスピノーダル分解についての新しい情報をえるにはもっと現実に近い系でのコンピューターシミュレイションによる解析が必要である。