Tuto Nakamura

Indirect Coupling of Nuclear Spins in Antiferromagnet with Particular Reference to MnF2 at Very Low Temperatures

Indirect coupling of nuclear spins through hyperfine interaction with spin waves is discussed in the case of antiferromagnetics at very low temperatures. The line width of the F/sup 19/ nuclear magnetic resonance in MnF/ sub 2/ at 1.4 K observed by Shulman and Jaccarino (~ 14 gauss) proves to come mainly from this coupling. The line width of the Mn/sup 55/ rssonance in MnF/sub 2/ is also evaluated to be about 600 gauss. (auth)

On the Quenching of Molecular Rotation of Ortho-Hydrogen in Solid State

where c is the concentration of ortho-hydrogen molecules, T the absolute temperature, and R the gas constant. It is an aim of this paper to inquire into the origin of these two terms. Through calculations by the method of moment expansion, the magnitude of fJ can be explained from the quadrupolar interactions among ortho-molecules, while the anisotropic nature of the valence and van der Waals forces is shown to be effective only as corrective terms. On the other hand, the appearance of a shows that the molecular rotation of an ortho-molecule surrounded by para-molecules should also be quenched. A possible mechanism of this phenomenon may be the rotation-vibration coupling, for which the valence and van der Waals forces should be exclusively responsible. However, we are not yet able to get a complete understanding of this quenching process. Deviation from the above formula, i. e. the linear dependence on c of the the quantity CvT2fR at temperatures not high enough is also derived and compared with experiment. Further, a more exact treatment than the moment expansion method is given for the case of low ortho-concentrations and is applied to the case of 7% ortho.

On the Spin Wave Theory of Magnetic Susceptibility and Resonance Absorption in Antiferromagnetics

A theory of resonance absorption in antiferromagnetics based on the spin wave theory developed by Anderson and Kubo is presented The obtained resonance frequencies are given by two sharp ones, which are compared with the results of the classical theory by Nagamiya. In both cases the anisotropy energy has uniaxial symmetry. The absorption coefficient is also computed. Our calculations of the resonance frequencies are then extended to the antiferromagnetics having the anisotropy energy of ortho· rhombic symmetry. In the course of these calculations we obtained expressions for the magnetic susceptibility, using the obtained energy levels of the spin system which is subjected to a static magnetic field. They are in agreement with those which Kubo has dready given by use of the method of statistical thermodynamics.

A Note on the Ground State of Antiferromagnetism

Kasteleijns method of obtaining the ground state of antiferromagnetism is generalized to the cases of two and three dimensional lattices. According to our generalization, the ground state of the three dimensional antiferromagnetic Heisenberg model with the spin quantum number equal to one half is paramagnetic in the absence of anisotropy energy. The magnetization of sublattices is calculated as a function of the degree of anisotropy. With increasing coordination numbers the anisotropy energy necessary for establishing the antiferromagnetic state decreases rapidly.

Modification of the Image Potential for the Interfacial Zone with Varying Dielectric Constant

The overall nature of the image potential term is studied classically for a flat interfacial zone, where the dielectric constant changes from e 1 to e 2 as a function of distance normal to the interface. A perturbation theoretic approach is taken, where γ=( e 1 - e 2 )/( e 1 + e 2 ) is shown to be a relevant expansion parameter. Results useful in treating the diffusive interface are given up to second order in γ.

Molecular Attractive Force in Small Cavities

In cavities of simple shape inside a dielectric, the molecular attractive forces are studied in the Drude-Lorentz model of molecule, by assuming the dielectric function of the medium to be of the single-resonance type. The retardation effect is neglected in view of pores of very small size. The medium correction to the intermolecular attractive force is shown to be anisotropic but of small magnitudes, for the distance of physical interest. The potential energy of a molecule coming also from the same origin is studied in details, because it must be a basic quantity in predicting features of the phase transition of condensed matter observed in pores.

Correlation Correction to the Thomas-Fermi-Dirac Statistical Model of Condensed Matter

Effect of the correlation energy on the Thomas-Fermi-Dirac statistical model of the condensed matter is studied systematically by means of a perturbation method. The pressure curves are obtained with main interest in the low pressure region where the correlation effect is appreciable. The instability of the statistical model occurring at a certain negative pressure is discussed in connection with the thermodynamical stability of electron gas in the outermost region of the Wigner-Seitz sphere, and with the binding problem for an aggregate of atoms at zero pressure.

Padé-approximant study of the phase transition of ortho–para mixtures in solid hydrogen

The phase transition of solid hydrogen is studied in the Pade approximation, with newly calculated coefficients in the high-temperature expansion series for the free energy. For the low-temperature phase, the free energy is obtained by a previous libron study of ortho–para mixtures. The transition temperature is predicted to be 2.1Γ for pure ortho-hydrogen. The phase transition disappears at ~ 60% of ortho-hydrogen, in agreement with experiment.