Recently it has been shown that many traditional models used for a description of dilute magnetic alloys are completely integrable and may be solved exactly without any approximation. In this article we summarize the results which have been obtained in this way. The main part of the article is devoted to the consistent and detailed account of the Bethe-Ansatz technique for the s-d exchange (Kondo) model with arbitrary impurity spin, s-d model with anisotropic exchange, degenerate exchange model and for the canonical Anderson model. The thermodynamic properties of a magnetic impurity in a non-magnetic metal host obtained by the Bethe method are considered in detail. Mainly attention is paid to the analysis of singularities associated with the formation of a localized moment, Kondo effect and mixedvalence phenomenon, which can be treated analytically. In the introductory part of the article we discuss the applicability of the models which we study in the paper to the real alloys and consider some m...

Exact results in the theory of magnetic alloys

IN many substances, changes in chemical composition, pressure or temperature can induce metal-to-insulator transitions1. Although dramatic changes in optical and electrical properties accompany such transitions, their interpretation is often complicated by attendant changes in crystallographic structure2. Yttrium, lanthanum and the trivalent rare-earth elements form hydrides that also exhibit metal–insulator transitions3–5, but the extreme reactivity and fragility of these materials hinder experimental studies5,6. To overcome these difficulties, we have coated thin films of yttrium and lanthanum with a layer of palladium through which hydrogen can diffuse. Real-time transitions from metallic (YH2 or LaH2) to semiconducting (YH3 or LaH3) behaviour occur in these films during continuous absorption of hydrogen, accompanied by pronounced changes in their optical properties. Although the timescale on which this transition occurs is at present rather slow (a few seconds), there appears to be considerable scope for improvement through the choice of rare-earth element and by adopting electrochemical means for driving the transition. In view of the spectacular changes in optical properties—yttrium hydride, for example, changes from a shiny mirror to a yellow, transparent window—metal hydrides might find important technological applications.

Yttrium and lanthanum hydride films with switchable optical properties

Ion beam crystallography of surfaces and interfaces

This review considers the experimental and theoretical studies of concentrated Kondo systems (CKS), Kondo lattices, substitutional solid solutions and their transition from Kondo impurity to Kondo lattice, and ‘intermediate valence compounds’ which are, in fact, high T K CKS (T K is the Kondo temperature). The anomalous low temperature properties of CKS are related to the formation of the narrow (∼k B T K) high-amplitude Abrikosov-Suhl resonance E R in the vicinity of the Fermi level E F. This resonance is situated exactly at E F in low T K CKS with T K ΔCF (ΔCF is the crystal field splitting). In low T K ‘j=1/2’ CKS the condition E R=E F leads to an increase of the density of states at E F, which is large enough to induce heavy fermion superconductivity in CeCu2Si2, UBe13. We demonstrate that the transition from low T K (E R=E F) to high T K CKS (E R≠E F) might be what was formerly considered as a ‘Kondo-lattice-intermediate valence state’ transition...

Concentrated Kondo systems

Measurement of the thermal boundary conductance (TBC) by use of a nondestructive optical technique, transient thermoreflectance (TTR), is presented. A simple thermal model for the TTR is presented with a discussion of its applicability and sensitivity. A specially prepared sample series of Cr, Al, Au, and Pt on four different substrates (Si, sapphire, GaN, and AlN) were tested at room temperature and the TTR signal fitted to the thermal model. The resulting TBC values vary by more than a factor of 3~0.71 310 8 ‐2.3310 8 W/m 2 K!. It is shown that the diffuse mismatch model (DMM) tended to overpredict the TBC of interfaces with materials having similar phonon spectra, while underpredicting the TBC for interfaces with dissimilar phonon spectra. The DMM only accounts for diffuse elastic scattering. Other scattering mechanisms are discussed which may explain the failure of the DMM at room temperature.@DOI: 10.1115/1.1857944#

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Measurement of Thermal Boundary Conductance of a Series of Metal-Dielectric Interfaces by the Transient Thermoreflectance Technique

The electronic structures of TiH/sub x/, ZrH/sub x/, and HfH/sub x/ have been studied using photoelectron spectroscopy and synchrotron radiation. Structures in the metal d-derived band within approx.3 eV of the Fermi level E/sub F/ and in the bonding band (approx.3--10 eV below E/sub F/) are compared with theory. In each dihydride, the bonding band center falls at -5.5 eV, at approximately the same energy as previously observed for the dihydrides of Sc and Y. Changes in the emission features near E/sub F/ and at -7 eV have been observed in samples bridging the fcc..-->..fct distortion in ZrH/sub x/, 1.63< or =x< or =1.94. The changes at E/sub F/ demonstrate the Jahn-Teller effect for the electronic states of ZrH/sub x/. The binding energies of the Ti 3p, Zr 4p, Hf 5p, and Hf 4f cores are observed to be greater than in the elemental metals, consistent with charge transfer to the hydrogen site.

Electronic structure of metal hydrides. IV. TiH/sub x/, ZrH/sub x/, HfH/sub x/, and the fcc-fct lattice distortion

Photoelectron-spectroscopy studies of Ce${\mathrm{Al}}_{2}$, La${\mathrm{Al}}_{2}$, and the "chemically compressed" alloys ${\mathrm{Ce}}_{0.6}$${\mathrm{Y}}_{0.4}$${\mathrm{Al}}_{2}$ and ${\mathrm{Ce}}_{0.6}$${\mathrm{Sc}}_{0.4}$${\mathrm{Al}}_{2}$ were performed with use of synchrotron radiation. For all compounds the $4f$ binding energy is 2.55 \ifmmode\pm\else\textpm\fi{} 0.1 eV. These results, combined with previous bulk-property results, motivate a reevaluation of Anderson-model parameters and mechanisms as applied to Ce${\mathrm{Al}}_{2}$.

Fundamental Parameters and Mechanisms in the Ce Problem: Photoemission Results on Ce Al 2 and Ce Al 2 Alloys

Structural morphology and electronic properties of the Si-Cr interface

The composition-dependent electronic structure of fcc $\mathrm{La}{\mathrm{H}}_{x}$, $1.9l~xl~2.9$, has been studied using photoelectron spectroscopy with synchrotron radiation ($10l~\mathrm{hv}l~50 \mathrm{eV}$). Complementary optical reflectance measurements ($0.16l~\mathrm{hv}l~4 \mathrm{eV}$) have been performed for fcc $\mathrm{La}{\mathrm{H}}_{x}$, $1.9l~xl~2.9$, and $\mathrm{Nd}{\mathrm{H}}_{x}$, $2.01l~xl~2.27$. For $\mathrm{La}{\mathrm{H}}_{x}$, $x\ensuremath{\simeq}2$, the occupied $d$ bands are \ensuremath{\sim}1.5 eV wide and the hydrogen-induced bonding band is centered \ensuremath{\sim}5 eV below the Fermi level, ${E}_{F}$ (full width \ensuremath{\sim}6 eV). Hydrogen occupation of both octahedral and tetrahedral sites is revealed for $xl~2$, analogous to what has been observed for other metal dihydrides. With increasing hydrogen concentration, emission from the $d$ bands near ${E}_{F}$ decreases and the bonding band shifts to higher binding energy; the optical spectra show a red shift of interband absorption features, increased octahedral site occupation, and increased screening of a low-energy plasmon. For $\mathrm{La}{\mathrm{H}}_{x}$ samples at the upper end of the composition range, $x\ensuremath{\sim}2.9$, the photoemission spectra show very weak valence-band emission, and the optical spectra suggest semiconducting behavior. The binding energies of the ${5p}_{\frac{1}{2},\frac{3}{2}}$ cores, ${E}_{B}$, measured relative to ${E}_{F}$ are shown to increase with $x$ (the total shift is \ensuremath{\sim}0.8 eV for La \ensuremath{\rightarrow} La${\mathrm{H}}_{2}$ and 0.9 eV for La${\mathrm{H}}_{2}$ \ensuremath{\rightarrow} La${\mathrm{H}}_{3}$). Our results are compared to band calculations by Gupta and Burger and by Misemer and Harmon and to results of NMR, specific heat, and resistivity studies.

D. J. Peterman

Papers

Electronic structure of metal hydrides. IV. TiH/sub x/, ZrH/sub x/, HfH/sub x/, and the fcc-fct lattice distortion

Fundamental Parameters and Mechanisms in the Ce Problem: Photoemission Results on Ce Al 2 and Ce Al 2 Alloys

Structural morphology and electronic properties of the Si-Cr interface

Electronic structure of metal hydrides. V. x-dependent properties of LaH/sub x/ (1. 9< or =x< or =2. 9) and NdH/sub x/ (2. 01< or =x< or =2. 27)

Ce 4f electron in CeH 2.1 , CeH 2.4 , CeAl 2 , CePd 3 , CeRh 3 , and CeRu 2 : A photoemission study using synchrotron radiation