277 research outputs found
Collapse of the ESR fine structure throughout the coherent temperature of the Gd-doped Kondo Semiconductor
Experiments on the Electron Spin Resonance (ESR) in the filled
skutterudite (), at temperatures
where the host resistivity manifests a smooth insulator-metal crossover,
provides evidence of the underlying Kondo physics associated with this system.
At low temperatures (below ), behaves
as a Kondo-insulator with a relatively large hybridization gap, and the
ESR spectra displays a fine structure with lorentzian line shape,
typical of insulating media. The electronic gap is attributed to the large
hybridization present in the coherent regime of a Kondo lattice, when Ce
4f-electrons cooperate with band properties at half-filling. Mean-field
calculations suggest that the electron-phonon interaction is fundamental at
explaining the strong 4f-electron hybridization in this filled skutterudite.
The resulting electronic structure is strongly temperature dependent, and at
about the system undergoes an insulator-to-metal
transition induced by the withdrawal of 4f-electrons from the Fermi volume, the
system becoming metallic and non-magnetic. The ESR fine structure
coalesces into a single dysonian resonance, as in metals. Still, our
simulations suggest that exchange-narrowing via the usual Korringa mechanism,
alone, is not capable of describing the thermal behavior of the ESR spectra in
the entire temperature region ( - K). We propose that temperature
activated fluctuating-valence of the Ce ions is the missing ingredient that,
added to the usual exchange-narrowing mechanism, fully describes this unique
temperature dependence of the ESR fine structure observed in
.Comment: 19 pages, 6 figure
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
Esr Of Au: Yb Thin Films: Crystal-field Effects And The Kondo Dilemma
ESR experiments at liquid-helium temperatures on Au: Yb thin films evaporated on quartz and NaCl substrates are reported. The anisotropy on the.2294161416
Unconventional Metallic Magnetism in LaCrSb{3}
Neutron-diffraction measurements in LaCrSb{3} show a coexistence of
ferromagnetic and antiferromagnetic sublattices below Tc=126 K, with ordered
moments of 1.65(4) and 0.49(4) Bohr magnetons per formula unit, respectively
(T=10 K), and a spin reorientation transition at ~95 K. No clear peak or step
was observed in the specific heat at Tc. Coexisting localized and itinerant
spins are suggested.Comment: PRL, in pres
Direct determination of the crystal field parameters of Dy, Er and Yb impurities in the skutterudite compound CeFeP by Electron Spin Resonance
Despite extensive research on the skutterudites for the last decade, their
electric crystalline field ground state is still a matter of controversy. We
show that Electron Spin Resonance (ESR) measurements can determine the full set
of crystal field parameters (CFPs) for the Th cubic symmetry (Im3) of the
CeRFeP (R = Dy, Er, Yb, )
skutterudite compounds. From the analysis of the ESR data the three CFPs, B4c,
B6c and B6t were determined for each of these rare-earths at the Ce
site. The field and temperature dependence of the measured magnetization for
the doped crystals are in excellent agreement with the one predicted by the
CFPs Bnm derived from ESR.Comment: 7 pages, 5 figures, to appear in PR
Self-Calibrated Double Luminescent Thermometers Through Upconverting Nanoparticles
Luminescent nanothermometry uses the light emission from nanostructures for temperature measuring. Non-contact temperature readout opens new possibilities of tracking thermal flows at the sub-micrometer spatial scale, that are altering our understanding of heat-transfer phenomena occurring at living cells, micro electromagnetic machines or integrated electronic circuits, bringing also challenges of calibrating the luminescent nanoparticles for covering diverse temperature ranges. In this work, we report self-calibrated double luminescent thermometers, embedding in a poly(methyl methacrylate) film Er3+- and Tm3+-doped upconverting nanoparticles. The Er3+-based primary thermometer uses the ratio between the integrated intensities of the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions (that follows the Boltzmann equation) to determine the temperature. It is used to calibrate the Tm3+/Er3+ secondary thermometer, which is based on the ratio between the integrated intensities of the 1G4→3H6 (Tm3+) and the 4S3/2→4I15/2 (Er3+) transitions, displaying a maximum relative sensitivity of 2.96% K−1 and a minimum temperature uncertainty of 0.07 K. As the Tm3+/Er3+ ratio is calibrated trough the primary thermometer it avoids recurrent calibration procedures whenever the system operates in new experimental conditions
Electron-spin-resonance And Lattice-parameter Study Of Cerium Cubic Laves-phase Compounds: Evidence For Intermediate-valence State
A lattice-constant study of the cubic C 15 Ce(IrxOs1-x)2 and Ce(PtxIr1-x)2 mixtures at room temperature reveals anomalous lattice constant versus x behavior. Also the electron-spin-resonance thermal broadening and g shift of Nd3+ in these compounds are anomalous but could be correlated with the lattice parameters. This is taken as evidence for intermediate-valence state in some of the mixtures. © 1980 The American Physical Society.45241966197
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
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