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a shift nor a broadening of the emitted line with respect to the incident line has been observed within the limits of error of ±3 A given by the resolution of the monochromator. Furthermore, the intensity of emission obtained by irradiating the foil with light of a narrow spectral width has been found to be the same as that obtained at the same frequency by irradiating the foil with a large frequency band (>1000 A). These results are in good agreement with the emission experiments made on silver. 4 Obviously, the plasma behaves like a resonator.The half-width of the emitted line is 400 A or 460 meV in good agreement with the energy-loss measurements. (However, these two values are not directly to be compared, since the width of the emitted line is dependent on the observation angle 6. It needs to be extrapolated to 9 = 0 in order to be compared with the half-width of the electron energy loss. For this purpose, the half-width has to be measured Recent theories differ as to whether a negative s-d exchange interaction between a localized-impurity moment in a dilute alloy and the conduction-electron spins will result in the formation below some critical temperature T c of a quasibound state analogous to the Cooper pair in the theory of superconductivity, 1 "" 3 or will merely cause a strongly temperaturedependent scattering of conduction electrons at low temperatures. 4 Electrical resistivity measurements over the three-decade temperature range from 40 mdeg to 40°K reported here for dilute alloys of iron in copper permit a clear choice between the two predictions. Preliminary susceptibility measurements on the same material also tend to support the bound-state model. Quantitative agreement below T c between Nagaoka's theory and the resistivity data permit T c and hence Kondo's exchange coupling constant J to be determined. Above T c serious disagreement is found with the predictions of pertur-as a function of 0. These experiments are in preparation. This correction, however, is not of great importance.)It may be added that the maximum of the emission can be found at longer wavelengths than 3300 A, depending on the conditions of evaporation; the minimum of the transmission (plasma-resonance absorption) is displaced in the same way.These experiments show that the plasma of free electrons, excited by light, also shows the phenomenon of plasma-resonance emission.\J. Brambring and H. . bation theory, heretofore considered by most authors to be valid in the region sufficiently far above this temperature. The high value of T c (16°K) and the observed absence of impurity-impurity interactions make dilute Cu-Fe a nearly ideal system for studying the quantitative features of the low-temperature state.The alloy samples were vacuum cast in alumina-coated spherical graphite molds 11 mm in diameter, using high-purity copper combined with a suitable quantity of a Cu-0.5%Fe master alloy to create the very dilute samples needed. The larger susceptibility sample was prepared from the same master in a similar mold of different shape. A...

Susceptibility measurements in fields from a few Oe to 1 kOe at temperatures down to 40 m°K show that the moment on the iron site is completely compensated at temperatures far below the Kondo temperature, at least at the high-field values. Correlation of these results with Mossbauer measurements reveals new information about the behavior of the low-temperature state formed in these alloys. The experimental technique used is discussed in detail. Some other properties of the copper-iron system are reviewed.

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