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Magnetization measurements of SrRuO3 and CaRuO3 confirm that SrRuO3 is ferromagnetic with TC = (160±5) °K and that CaRuO3 has antiferromagnetic exchange interactions dominant. They further identify in CaRuO3 a Néel temperature TN = (110±10) °K and parasitic ferromagnetism below TN having a σ0 = (3.2±0.4) × 10−2 emu/g at 4.2°K. High-field (to 125 kOe) magnetization and neutron-diffraction data for SrRuO3 are consistent with a reduced spontaneous ferromagnetic moment μ0 = (1.4±0.4) μB and no ordered antiferromagnetic component. Resistivity measurements confirm a low resistivity (ρ<10−3Ω·cm) at room temperature having a metallic temperature coefficient. It is concluded that both compounds represent spontaneous collective-electron magnetism and that the reduced moment of SrRuO3 is due to holes in both the up-spin and down-spin bands. Antiferromagnetic CaRuO3 is predicted to have narrower ``4d'' bands.

A model is proposed for the line shape of the optical dielectric function of zinc-blende semiconductors. For comparison with previously proposed models, this model is used primarily with spectroscopic ellipsometry data (but also transmission data below 1.5 eV) to obtain an analytic room-temperature dielectric function for GaAs. It is found to be more generally valid than the harmonic-oscillator model, the critical-point (CP) model, or the model of Adachi. It is applicable over the entire range of photon energies, below and above the lowest band gaps, incorporates the electronic band structure of the medium, and exactly satisfies the Kramers-Kronig transformation.It goes beyond the CP parabolic-band approximation in that it correctly takes into account the full analytic form of the electronic density of states and thus does not require the use of arbitrary cutoff energies. Also, it allows one to go beyond the usual approximation of Lorentzian broadening, which is known to be incorrect for elements and compounds above very low temperatures. For these reasons, it results in excellent quantitative agreement with experimental results for the dielectric function and for its derivatives with respect to photon energy, much better than that given by earlier models. Finally, the parameters of the model are physically significant and are easily determined as functions of composition for semiconductor alloys. Application of the model to the fitting of spectroscopic data on GaAs strongly suggests that spectroscopic ellipsometry does not measure the true bulk dielectric function. It also supports the conclusion that the line-shape broadening in GaAs at room temperature is more nearly Gaussian than Lorentzian.

Crystallographic, magnetic, and electrical studies of the system La1−xSrxCoO3.00±0.01 for 0≤x≤0.5 give indirect evidence for the presence of chemical inhomogeneities separating strontium-free regions, where localized ``3d'' electrons occur at thermally excited high-spin Co3+ ions, from strontium-rich regions, where the ``3d'' electrons are collective and give ferromagnetism at low temperatures. These different regions occur within the same rhombohedral perovskite crystal and appear to represent two different electronic phases within the same crystallographic phase. A schematic band model for the ferromagnetic phase is presented.

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It is argued that there is a critical cation-anion covalent mixing parameter λc such that ligand-field theory is appropriate for λ<λc, but band theory must be used for λ>λc. This provides, therefore, a criterion for distinguishing metallic vs magnetic compounds in those structures, like perovskite, where cation-cation interactions are negligible. It is also argued that λσ>λc can be anticipated where the cations are in a low-spin state. The fact that LaNiO3 contains low-spin NiIII and exhibits no Jahn-Teller distortion suggested that λσ>λc in this compound. Metallic conductivity from −200° to 300°C and Pauli paramagnetism from 4° to 300°K seem to confirm this suggestion. Where λ≈λc, there is the possibility of a phase change in which λ<λc in some directions, λ>λc in others. LaCoO3 seems to illustrate this situation. It undergoes a transition at 1210°K, the cobalt ordering into alternate (111) planes of high-spin Co3+ and planes containing low-spin CoIII. Below 400°K the latter planes contain only CoIII ions. The magnetic Co3+ ions couple antiferromagnetically via Co3+-``diamagnetic CoIIIO6 complex''-Co3+ superexchange to give TN≈90°K.

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