Chiaki Uyeda

High Field Magnetization of Solid Oxygen

High field magnetization of solid oxygen is measured in the pulsed field up to 500 kOe. The spin flop field H c in the antiferromagnetic α-phase is investigated in detail and exchange and anisotropy fields are evaluated. The obtained data are compared with previously determined parameters and magnetic properties of three solid phases are satisfactorily explained. The α-phase is two-dimensional antiferromagnet with intrinsic Neel temperature of 30 K and the β-phase consists of the triangular spin short range order while the one-dimensional short range order exists in the A-15 type γ-phase. The corresponding exchange constants in these phases are determined by using the theory of low-dimensional magnetism and a systematic change is obtained throughout three phases.

Diamagnetic Orientation of Clay Mineral Grains

The orientations of diamagnetic mineral grains in magnetic fields are observed, for the first time, in suspensions of clay minerals such as talc, kaolinite and sericite. The minerals consist of two-dimensional crystal layers which produce intrinsic diamagnetic anisotropy, Δχ, in the unit cell. In the case of talc suspension with the average diameter of φ 2.4 µm and the thickness of 0.2 µm, the grains show full orientation in a magnetic field of less than 0.5 T. As the size of the grains becomes smaller, full orientation is achieved with higher fields. This size dependence occurs because the field-induced anisotropic energy of a grain is proportional to N Δχ, where N is the number of unit cells in the grain.

Magnesium isotopic fractionation of silicates produced in condensation experiments

Isotopic mass fractionations of magnesium have been studied for silicates produced in condensation experiments for the purpose of studying the evaporation-condensation process in the early solar nebula in connection with the isotopic data observed in various primitive materials. The silicate gas, which is evaporated from forsterite, was fractionated to produce condensates at various temperatures below 1350°C down to room temperature, and the amount of isotopic mass fractionation varied considerably with the condensation temperature,Tc. The variation in the 26Mg/24Mg ratio with respect to the initial evaporation source, Δ26, varies from +8‰ to −30‰ asTc changes from 1350°C to room temperature. The obtained(Δ26) - Tc relationship is explained in terms of the Rayleigh fractionation model, and the relationship indicates that the condensates fractionate isotopically toward the heavy mass with respect to the gas phase at temperatures from 700°C to 1350°C. The obtained data show that the condensates can be fractionated both toward the heavy and light isotopes with respect to the initial source according to the fraction of the residual gas phase,ƒ(Tc). The evaluation of mass fractionation between the condensed phase and the residual gas phase is essential for the analysis of various isotopic data on primitive materials.

Diamagnetic Anisotropy of Silicates Composed of Tetrahedral Networks

Small diamagnetic anisotropy, (Δχ) DIA , on the order of 10 -9 to 10 -10 emu/g was detected for four silicates by the use of the field-induced harmonic-oscillation method in the high-temperature re...

Diamagnetic Anisotropy Derived from Single Chemical Bonds in the Silicate Tetrahedral Networks

The diamagnetic anisotropy (Δχ) DIA derived from the individual bonding orbitals of the silicate [TO 4 ] networks is estimated from the observed results on α-quartz [SiO 2 ], orthoclase [KAlSi 3 O 8 ] and apophyllite [Ca 4 KF(Si 4 O 10 ) 2 , 8H 2 O]. The (Δχ) DIA value of individual chemical bond was estimated to be -3.5×10 -30 emu/mol, the uniaxial principal axis being parallel to the bond direction. The calculated results indicate that the bond direction is the magnetically unstable axis. This result is compatible with the observed and calculated distributions of electron density for the T–O orbitals, which are preferentially spread in the direction off the bond direction.

Diamagnetic anisotropies of oxide minerals

The diamagnetic anisotropy of oxide minerals is analyzed in terms of a new model, in which the anisotropy is assigned to the individual chemical bond in the [MO6] octahedral unit of the crystal. The diamagnetic principal axis of the individual M-O bond is assumed to be parallel to the direction of the bond. The calculated anisotropy based on this model shows a good correlation with the measured diamagnetic anisotropy, Δχ, for various minerals such as talc, sericite, kaolinite of the sheetsilicate group, forsterite of the orthosilicate group, and corundum of the hematite group. The Δχ values of many diamagnetic minerals are still unknown since the measurement is difficult to perform by means of conventional methods. The magnetic grain orientation recently observed in the mineral suspensions is effective for estimating the Δχ value, when the single crystal of the mineral cannot be obtained. The observation of fieldinduced crystal oscillation in the high magnetic fields can be applied for measuring the minerals with small Δχ values of less than 5 × 10−10 emu/cc. The chemical bond model on the diamagnetic anisotropy can be confirmed, when the compiling of Δχ data on various mineral is made by means of the above two methods.

Liquid oxygen under high magnetic field

A systematic study of liquid oxygen under a high magnetic field is described. It is found that the experimental results of the field-induced transparency are not explained by the simple mean field method even though the magneto-volume effect, which enhances the field-induced transparency, is taken into account. The transparency effect is quantitavely explained by the spin-pair model where two spins of the O 2 molecule pair couple with each other. The conclusion seems to be probable because the optical transition comes from one photon absorption by two ground state ( 3 Σ g - ) molecules where the pair interaction may play an important role.

Diamagnetic anisotropy of sheetsilicates

The diamagnetic properties of sheetsilicates are studied by measuring the magnetic orientation of micron-sized crystals. In the case of synthetic phlogopite with the average diameter of 0.65 μm and the thickness of 0.2 μm, the alignment of the grains is achieved in the magnetic field below 35 kOe. The planes of the platy single-crystal grains were alignned parallel to the field when the alignment was achieved. The alignment of the grains is realized because the field-induced anisotropic energy, caused by the diamagnetic anisotropy in the minerals crystal structure, exceeds thermal agitation energy in the applied field. By analyzing the field dependence of grain alignment, the diamagnetic anisotropy per formula unit, Δχ, of sheetsilicate mineral is estimated even if a large single crystal is not provided. The field-induced anisotropic energy is proportional to NΔχ where N is the number of molecules in the grain.A linear correlation has been found between the Δχ value and the F/OH mole ratio among the measured sheetsilicates. This correlation supports the assumption that the hexagonally packed oxygen-layer in the crystal lattice induces the anisotropies of the sheetsilicates.

Magneto-Volume Effect of Liquid Oxygen

A large magneto-volume effect is found in liquid-phase oxygen. The volume expansion Δ V / V 0 is 2.2×10 -4 under the field of 80 kOe, which is about ten times larger than that in ferromagnetic Fe, Co or Ni metals. The effect is understood by the exchange repulsion between O 2 spins polarized by an external magnetic field. The contribution of the magneto-volume effect to field-induced transparency is discussed.

Determination of the Spin Flop Field in High Field Magnetization of Polycrystalline Antiferromagnet

The high field magnetization of a polycrystalline orthorhombic antiferromagnet is calculated by changing the ratio of the orthorhombic anisotropy energies K 2 / K 1 . It turned out that the peak of d M /d H curve always appear at the spin flop critical field H c , independent of the ratio of K 2 / K 1 . The calculated d M /d H curves coincide well with various experimental data.