526 research outputs found
Magnetic Properties of a-Si films doped with rare-earth elements
Amorphous silicon films doped with Y, La, Gd, Er, and Lu rare-earth elements
(a-Si:RE) have been prepared by co-sputtering and studied by means of electron
spin resonance (ESR), dc-magnetization, ion beam analysis, optical
transmission, and Raman spectroscopy. For comparison the magnetic properties of
laser-crystallized and hydrogenated a-Si:RE films were also studied. It was
found that the rare-earth species are incorporated in the a-Si:RE films in the
RE3+ form and that the RE-doping depletes the neutral dangling bonds (D0)
density. The reduction of D0 density is significantly larger for the magnetic
REs (Gd3+ and Er3+) than for the non-magnetic ones (Y3+, La3+, Lu3+). These
results are interpreted in terms of a strong exchange-like interaction, J RE-DB
SRE SDB, between the spin of the magnetic REs and that of the D0. All our
Gd-doped Si films showed basically the same broad ESR Gd3+ resonance (DHpp ~
850 Oe) at g ~ 2.01, suggesting the formation of a rather stable RE-Si complex
in these films.Comment: 15 pages, 7 figure
Surface magnetic canting in a ferromagnet
The surface magnetic canting (SMC) of a semi-infinite film with ferromagnetic
exchange interaction and competing bulk and surface anisotropies is
investigated via a nonlinear mapping formulation of mean-field theory
previously developed by our group [L. Trallori et al., Int. J. Mod. Phys. B 10,
1935-1988 (1996)], and extended to the case where an external magnetic field is
applied to the system. When the field H is parallel to the film plane, the
condition for SMC is found to be the same as that recently reported by Popov
and Pappas [Phys. Rev. B 64, 184401 (2001)]. The case of a field H applied
perpendicularly to the film plane is also investigated. In both cases, the
zero-temperature equilibrium configuration is easily determined by our
theoretical approach.Comment: 4 pages, 3 figure
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
Phase Transition In Alcl3-graphite As Seen By The Thermal Hysteresis In The Conduction-carrier Spin Resonance
A phase transition at 168 K has been recognized from the thermal hysteresis of the conduction-carrier spin-resonance parameters in the stage-7 acceptor AlCl3-graphite intercalated compound (GIC). Below the transition temperature, the final low-temperature in-plane residual resistivity of the sample was found to be dependent on its previous thermal history. Paradoxically, quenching effects, contrary to previous reports on low-stage acceptor GICs, leave the system in an orderedlike state of higher in-plane conductivity. © 1985 The American Physical Society.3274774477
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
Thermally activated exchange narrowing of the Gd3+ ESR fine structure in a single crystal of Ce1-xGdxFe4P12 (x = 0.001) skutterudite
We report electron spin resonance (ESR) measurements in the Gd3+ doped
semiconducting filled skutterudite compound Ce1-xGdxFe4P12 (x = 0.001). As the
temperature T varies from T = 150 K to T = 165 K, the Gd3+ ESR fine and
hyperfine structures coalesce into a broad inhomogeneous single resonance. At T
= 200 K the line narrows and as T increases further, the resonance becomes
homogeneous with a thermal broadening of 1.1(2) Oe/K. These results suggest
that the origin of these features may be associated to a subtle interdependence
of thermally activated mechanisms that combine: i) an increase with T of the
density of activated conduction-carriers across the T-dependent semiconducting
pseudogap; ii) the Gd3+ Korringa relaxation process due to an exchange
interaction, J_{fd}S.s, between the Gd3+ localized magnetic moments and the
thermally activated conduction-carriers and; iii) a relatively weak confining
potential of the rare-earth ions inside the oversized (Fe2P3)4 cage, which
allows the rare-earths to become rattler Einstein oscillators above T = 148 K.
We argue that the rattling of the Gd3+ ions, via a motional narrowing
mechanism, also contributes to the coalescence of the ESR fine and hyperfine
structure.Comment: 7 pages, 9 figures, accepted for publication in Phys Rev
Conduction electrons in aperiodic versus periodic structures: an ESR study of quasicrystalline i-Y(Gd)-Cd and its approximant Y(Gd)Cd-6
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORA formal description of collective electronic states in condensed-matter systems lacking long-range periodicity remains a theoretical challenge. To experimentally explore the differences in electronic and magnetic behavior between metallic quasicrystals (QCs) and their conventional crystalline analogs [quasicrystal approximants (QCAs)], we have grown single crystals of Y1-xGdx-Cd6 (QCA) together with their QC counterparts i-Y1-xGdx-Cd for x = 0.006, 0.01, 0.1, and 1.00, and we carried out comparative T-dependent electron spin resonance (ESR) measurements. On the high Gd concentration side, x = 1.00, we confirm that GdCd6 adopts an antiferromagnetic ground state below T-N similar to 22 K, whereas i-Gd-Cd presents spin-glass-like behavior showing similar local and dynamical properties from the point of view of ESR. For the diluted samples, our ESR experimental results show similar local conduction electron polarization behavior at the Gd3+ site in all QC/QCA pairs investigated, supporting the validity of using QCAs as periodic representations of QCs in terms of short-range electronic interactions. However, there is a measurable difference in the Korringa relaxation rate (spin-flip relaxation process between the localized Gd3+ 4f electron and the delocalized s-type conduction electrons at the Fermi surface) between the QC/QCA pairs probably associated with the lack of periodicity. We expect that our comparative ESR study may provide support and motivation for the development of new theoretical approaches toward a generalized band-structure theory, contemplating condensed-matter systems beyond the scope of traditional periodicity.100117FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIOR2016/15780-02011/19924-2Sem informaçãoSem informaçã
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
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