M. Tachiki

Thermopower in Ce Kondo systems

The giant thermopower in metals with Ce 3+ impurities is theoretically studied. The relaxation time of a conduction electron is calculated as a function of energy in the selfconsistent ladder approximation by applying Abrikosovs pseudofermion technique to the Coqblin-Schrieffer exchange model with crystal field. The thermopower as well as the electrical resistivity exhibit universal behaviors if the crystal field is neglected. The crystal field induces the characteristic features and the anisotropy in the thermopower versus temperature curve. However, the sign of the thermopower is always positive in Ce system in contrast with Yb systems.

Effect of Crystal Field on Kondo Resistivity in Ce Compounds

The effect of crystal field on Kondo resistivity in metals with Ce impurities is theoretically studied. The T -matrix of conduction electron is calculated in the self-consistent ladder approximation by applying Abrikosovs pseudofermion technique to the Coqblin-Schrieffer exchange model. The numerical results of the resistivity in cubic and tetragonal crystals are compared with the experimental ones in Ce x La 1- x Al 2 and CeCu 2 Si 2 . Our theory provides a unified view of the magnetic and transport properties in Ce compounds and alloys.

Collective Motion of Spins in Ferro- and Antiferromagnets+

+ A brief account of the present work is published in the proceedings of the International Conference on Magnetism and Crystallography in Kyoto, published by the Physical Society of Japan, 1962. A new approach to the calculation of the temperature dependence of spin wave frequencies in ordered spin state is proposed. The results for ferromagnets agrees with Keffers expression. Spin wave frequencies in antiferromagnets in the presence of an anisotropy energy are also calculated. By the present approach it is shown that the antiferromagnetic resonance frequency can be expressed phenomenologically in terms of anisotropy constants and static susceptibilities. The obtained expression of the resonance frequency is valid in any statistical approximation. The observed temperature dependence of the resonance frequency in MnF 2 is discussed by use of this result.

Deposition conditions of magnetoresistance in La0.67Ca0.33MnO3−δ thin film

Magnetoresistance of the La0.67Ca0.33MnO3−δ thin films was investigated. The magnetoresistance depends on ablation conditions such as the substrate temperature and oxygen pressure and has a relation with the lattice constants of the thin films. A colossal magnetoresistance ratio with 4.79×106% was obtained at 70 K and a magnetic field of 5.5 T. The resistivity of the thin films has a close relation with the substrate temperature and the oxygen pressure. When the substrate temperature is fixed, the resistivity shows double peaks in the oxygen pressure range of 1×10−7 to 1 Torr.

Origin of the Magnetic Anisotropy Energy of Antiferromagnetic Cr2O3

The magnetic anisotropy constant Cr 2 O 3 arising from the dipolar interactions among the chromic ions was calculated to be -0.059 cm -1 per ion at absolute zero, and the magnetic anisotropy constant due to the crystalline field combined with the spin-orbit coupling was estimated from the fine-structure coupling constant of ruby and compared with that deduced from the antiferromagnetic resonance experiment by Dayhoff. The value from ruby is too large. The temperature dependence of the anisotorpy constant and that of the antiferromagnetic resonance frequency at zero field are discussed.

Crystal field and Kondo effect in Ce compounds

Abstract The static and dynamical susceptibilities in Ce compounds and alloys are studied theoretically, taking into account Kondo effects and crystal fields self-consistently. A quantitative comparison of the neutron scattering spectra is made with the experimental data in CeCu 2 Si 2 , Ce x La 1− x Al 2 and CeB 6 .

Kondo effect on crystal field splitting

A theory is developed for the temperature dependence of crystal field energy levels of Ce ions in metals caused by the Kondo effect. Abrikosov’s pseudofermion technique is applied to the Coqblin–Schrieffer exchange model, and the self energy is derived in the self‐consistent ladder approximation. The neutron quasi‐elastic and inelastic scattering spectra are calculated in the system with cubic crystal field.

Exchange Contribution to theD-Parameter of Mn2+in CoCl2·2H2O

The D -value of Mn 2+ in CoCl 2 ·2H 2 O has been obtained to be -0.13 cm -1 by Date and Motokawa. The large negative D value is reasonably explained by introducing an effective exchange interaction of general form between the Mn 2+ and the ground Kramers doublet of Co 2+ , taking account of the crystal symmetry. It is shown that the interaction -2 J x z s x S z -2 J y z s y S z is responsible for the negative D -parameter. The effective exchange interaction is derived from the nondiagonal exchange between Mn 2+ and Co 2+ with respect to the cobaltous orbits by projecting the exchange to the ground Kramers doublet.The D -value of Mn 2+ in CoCl 2 ·2H 2 O has been obtained to be -0.13 cm -1 by Date and Motokawa. The large negative D value is reasonably explained by introducing an effective exchange interaction of general form between the Mn 2+ and the ground Kramers doublet of Co 2+ , taking account of the crystal symmetry. It is shown that the interaction -2 J x z s x S z -2 J y z s y S z is responsible for the negative D -parameter. The effective exchange interaction is derived from the nondiagonal exchange between Mn 2+ and Co 2+ with respect to the cobaltous orbits by projecting the exchange to the ground Kramers doublet.

Susceptibility and Antiferromagnetic Resonance in Cobaltous Oxide

The magnetic susceptibility and antiferromagnetic resonance of CoO are studied on the basis of Kanamoris theory, in which the residual orbital angular momentum plays an important role in the magnetic properties of CoO. The parallel susceptibility does not vanish at 0°K due to the unquenched orbital angular momentum. The calculated parallel, perpendicular, and powder susceptibilities are in good agreement with measured values. The antiferromagnetic resonance modes and frequencies are calculated by the method of using fictitious magnetic fields. In the absence of an external field there are four modes, which are pair-wise degenerate. The obtained frequencies at 0°K are 5.76×10 12 sec -1 and 16.61×10 12 sec -1 , which correspond to far-infrared wavelengths of 52.0 microns and 18.1 microns, respectively.

Kondo-like Effect of Atomic Motion in Amorphous Superconductors

Effects of tunneling motion of atoms characteristic in glass systems on superconductivity is theoretically studied. The pair-breaking mechanism of superconductivity proportional to [ln ( T / D )] 2 is derived in the fourth order of the Coulomb interaction between conduction electrons and atoms, where T is the temperature and D is the band width. We propose that the pair-breaking mechanism is an origin of the universal absence of the Maki term in the paraconductivity in amorphous superconductors.