Stress Effects On The Electron-spin-resonance Spectra Of Er In Gold And Silver Thin Films

Electron-spin-resonance measurements were carried out at liquid-helium temperatures on diluted Er in Au and Ag thin films (300-5000) evaporated on NaCl and quartz substrates. The observed anisotropy of the g value, linewidth, and line shape are explained by the mixing of excited crystalline field levels with the 7 ground state: These admixtures are caused by the stresses induced by the difference between the thermal expansion coefficients of the substrate and the film. Lower limits for the tetragonal and trigonal second-order orbit-lattice coupling parameters can be estimated from the data. In Au their magnitude and sign agree with those predicted by the point-charge model, while in Ag the trigonal parameter does not. Qualitative information about the strain distribution across the film was obtained by employing the anisotropy of the g value, the linewidth, and the line shape together with x rays and electron-microscopy analysis. © 1981 The American Physical Society.2373149315

Comment On The Gd Crystalline Field And The Gd-pr Exchange In The Van Vleck Monopnictides

We report on the observation of resolved fine structure in the ESR of Gd in PrSb, TmSb, and PrBi single crystals. The fourth-order crystalline-field parameter b4 was found to increase with the lattice constant upon going from the antimonides to the bismuthides, consistent with the variation of b4 in the analogous nonmagnetic pnictides. A correlation between b4 and the Korringa rate in the analogous nonmagnetic compounds suggests that the variation of b4 is associated with conduction-electron effects. Also the variation of the Gd-Pr exchange parameter, JGd-Pr across the pnictides is attributed to variation of the conduction-electron d-d overlap. The data enable us to estimate the pressure derivative of b4 and JGd-Pr. © 1979 The American Physical Society.1942385238

Electron Spin Resonance Of Nd3+ And Gd3+ In D-band Intermetallic Compounds

We report on the ESR of the rare-earth ions Nd3+, Gd3+, Er3+, and Yb3+ on powdered samples of various intermetallic compounds of AB2 cubic structure where B is a transition-metal ion belonging to the group VIII of the Periodic Table, and A is a nonmagnetic ion (La, Ce, Y). The resonance of the Nd3+ in these compounds originates within a Γ6 crystal-field ground level and exhibits resolved hyperfine satellites for the Nd143 and Nd145 isotopes. The Gd3+ spectra show a single isotropic line. Using our data for Gd3+ and Nd3+ together with results previously published for the AB2 cubic compounds, we were able to show a correlation between the observed g shifts and the position of the B ion in the Periodic Table. This variation is explained qualitatively using a simple multiband model, as well as band-structure arguments. The hyperfine constants for the Nd143 and Nd145 isotopes were found smaller in magnitude with respect to the values in insulators; this effect is attributed to s-electron self-polarization due to the Nd localized-moment-s-electron exchange coupling. The ESR linewidths of LaIr2: Nd and LaRh2: Nd exhibit an exponential thermal dependence at high temperatures which is attributed to the presence of a Γ8 excited level at Δ=90±20 K. © 1979 The American Physical Society.19115495550

Stress Effects On The Esr Spectra Of Dy In Ag Thin Films

ESR experiments on dilute Ag: Dy thin films at liquid-helium temperatures allow the estimation of lower limits for the second-order orbit-lattice coupling parameters. The anisotropy observed on the g value of the 7 ground state of Dy is interpreted in terms of admixtures of excited crystal-field levels with the ground state, via a planar strain of the film, induced by the difference in the thermal-expansion coefficients between the film and the substrate. The results indicate that the tetragonal orbit-lattice parameter agrees in sign with that predicted by the point-charge model, but the trigonal one does not, similar to Ag: Er thin films. © 1980 The American Physical Society.211343

Characteristcs chemical and soil salinization in the Irrigated District of California, SE, Brazil

O manejo inadequado da irrigação pode resultar no acúmulo de sais no solo, cuja intensidade depende da qualidade da água utilizada na irrigação, da fração de lixiviação adotada e da demanda evapotranspirativa da região. O presente trabalho teve como objetivo avaliar os atributos físicos e químicos dos solos do perímetro irrigado Califórnia, localizado no extremo noroeste do Estado de Sergipe. Para tal, foram realizadas amostragens em 42 lotes, correspondendo a 16,4% dos lotes deste perímetro. As maiores concentrações de sais e de sódio ocorreram na camada superficial (0–0,2m) do solo, o que evidenciou a falta de um manejo da irrigação adequado visando ao controle da salinidade. O aumento do pH do solo foi correlacionado significativamente com a porcentagem de sódio trocável, atingindo valores acima de 9,5. Correlações positivas significativas foram observadas entre a condutividade elétrica e os teores de Ca e Mg, indicando que sais desses íons podem estar se acumulando no solo pela ascensão do lençol freático, associado à ausência de lixiviação e drenagem. _________________________________________________________________________________________ ABSTRACT: The improper irrigation management may result in the accumulation of salts in the soil profile, which intensity depends on the irrigation water quality, the leaching fraction adopted and on the evapotranspiration demand of the region. The objective of the present study was to study the physical and chemical characteristics of the soils in the irrigated district of California, located in the northwest of the State of Sergipe. Thus, soil sampling were made in 54 lots, corresponding to 16.4% of the lots of this district. The highest salt and sodium concentrations occurred in the shallowest soil layer (0–0.2m), evidencing the lack of an appropriate irrigation management in order to control the salinity build up. The increasing of the soil pH was significantly correlated to the exchangeable sodium percentage, reaching values over 9.5. Significant positive correlations were observed between the electrical conductivity and the Ca and Mg content, indicating that salts of both ions could be accumulating in soil by the capillary rise of the water table, associated to the lack of leaching and drainage