Syoiti Kobayasi

Calculation of the Energy Band Structure of the β-SiC Crystal by the Orthogonalized Plane Wave Method

The energy band structure of the β- (zincblende-type) SiC crystal is worked by the orthogonalized plane wave (OPW) method. Since this crystal will be the typical one of the IV–IV compounds, the results of calculation for its electronic structure will be useful for systematic understanding of the transitions of the electron-behavior from the group-IV valence-crystals to the III–V compounds etc.. Our results show that the conduction band-minima occur at X -point or its immediate neighbor, while the valence band-maximum perhaps at \(\varGamma\)-point. Hence the indirect interband-transitions in the long wave limit will be expected to occur between these two states with the energy difference of 2.2 ev, and the direct interband-transitions at X -point will take place at a photon energy of 6.3 ev. Further the approximate charge-distribution in the crystal is worked by making use of the obtained \(\varGamma\)-valence eigenfunctions, which result seems to show that the electrons in its \(\vec{k}{=}0\) levels of t...

Numerical calculation of isomer shift on Eu151

Abstract On the isomer shift of the Mossbauer effect on Eu151, Brix et al., Shirley et al. and Nowik and Ofer have recently measured large values: -1.5 and -0.8 cm/sec for Eu2+-compounds and b.c.c. Eu metal relative to Eu3+- compounds, respectively. In order to clarify the origin of the phenomena, we have calculated first of all the energy band structure of b.c.c. metallic Eu by using Greens function method. We have obtained u nor Γ 1 (0)=+2.83 a H −3 2 , which leads to 2 Σoccck | ψk(0)|2=ξ×1.08×1026 cm-3, (ξ∼1), as the contribution of conduction electrons. This value is in good agreement with Brixs estimation from his and others experiment: +0.9 × 1026 cm-3. Furthermore, the difference between the isomer shifts for Eu3+ - and Eu2+- compounds is well understood by our present calculations of 5s wave functions in both crystals.

On Indirect Knight Shift and NMR in Ferromagnetic Metals Part I. General Formulation and Qualitative Discussions

It is well-known that the exchange-polarized core s -electrons by partially filled magnetic d -band electrons are able to make characteristic contributions to effective magnetic field felt by nucleus within crystal, which leads to temperature-dependent and negative Knight shift (indirect Knight shift) and nuclear magnetic resonance absorption in ferromagnetic metals. The mentioned exchange-polarization of core s -electrons has been worked out quantitatively only for the case of isolated atom and ion, and the extension to the crystal electrons in energy band has not been worked as yet mainly for the formidable labour of numerical computations. In view of the above situation we have adopted the perturbation-theoretic approach for working the mentioned problem. The empirical formula of indirect Knight shift by Clogston et al. and of NMR in ferromagnetic metals by Portis et al. have been derived successfully and the extension of our formalism to dilute ferromagnetic alloys has been worked.

On Indirect Knight Shift and NMR in Ferromagnetic Metals Part III. Numerical Calculation of NMR Frequency and Hyperfine Field in Ni, Co and Fe

By using our theoretical formula derived in part I, the numerical computation of the hyperfine fields in ferromagnetic nickel and cobalt has been performed in addition to a revised calculation of that in ferromagnetic iron. By taking appropriate values of the effective nuclear charge involved in 3 d -atomic orbital ( Z ) and of the mixing amount of 4 s wave function into the 3 d band (η·10 -2 ) the obtained results are found to show remarkably good agreements with the experiments, allowing for the various approximations involved in deriving our theoretical formula. In conclusion a simple band theory of ferromagnetic metals together with the perturbation-theoretic approach to exchange-polarization of crystal electrons seems to be quite useful for explaining the currently available observed results of NMR and the corresponding hyperfine field of ferromagnetic metals.

Fermi surface and helical spin ordering in Eu metal

Abstract The band structure and the Fermi surface of the b.c.c. Eu metal have been calculated by the non-relativistic KKR method. The obtained Fermi surface is grossly similar to that of Andersen and Loucks. We should like, however, to point out essential differences. Our electron surface around H is shaped like a sphere with eight low mounds in eight directions near the HP -axes (called “bumpy sphere”). Our hole surface around P is shaped like a “rounded-off cube”, as was obtained by Andersen and Loucks, but the cross-section perpendicular to the HP -axis for the tetrahedrally located wing (or island) is shaped like a “truncated-triangle”, not like an ellipse. The helical spin ordering at low temperatures can be understood on the basis of the hole Fermi surface. The electron surface around H does not seem to concern the nesting. Some other phenomena are also considered briefly.

Role of the Electron Fermi Surface in the Helical Spin Ordering of Rare Earth Metal Eu

Band structure and the detailed form of the Fermi surface of bcc Eu metal are calculated by the KKR method by using various exchange potentials of X α-type with α=2/3, 0.8, and 0.9. Already in 1976 and 1977, we have made a similar calculation with α=1 and have concluded that the electron Fermi surface is rather sphere-like on the contrary to the conclusion of Andersen and Loucks. Now in the present calculation, we confirm the fact that the previous conclusion is still kept valid even when the exchange potential is varied. Thus, we understand that the electron Fermi surface does not make practical contribution to the “nesting” phenomenon in the helical spin ordering of this metal.

On Inequality of Knight Shifts for Li6 and Li7

The isotope effect of Knight shift is discussed using both K/sub o/ and K/sub i/, the Knight shift for rigid lattice and the effect of lattice vibrations, respectively. (R.E.U.)

Band structure and the fermi surface of rare earth metal europium

Abstract In order to understand consistently the origin of the helical spin ordering of the bcc Eu observed below TN = 91 K, we have calculated the band structure and investigated the detailed shape of the Fermi surface, by the KKR method. The present results are compared with those of the previous calculations.

Calculation of the de Haas-van Alphen frequencies and the fermi surfaces of europium☆

Abstract Electronic energy bands of b.c.c. europium were calculated selfconsistently using the Korringa-Kohn-Rostoker method. Detailed shapes of the electron and hole Fermi surfaces were obtained. On the basis of these results, the de Haas-van Alphen frequencies were predicted for various applied magnetic field directions.