36 research outputs found
Spin dynamics of observed by Electron Spin Resonance
Below the Kondo temperature electron spin resonance (ESR) usually
is not observable from the Kondo-ion itself because the characteristic spin
fluctuation energy results in a huge width of the ESR line. The heavy fermion
metal YbRhSi seems to be an exceptional case where definite ESR
spectra show characteristic properties of the Kondo-ion Yb well
\textit{below} . We found that the spin dynamics of
YbRhSi, as determined by its ESR relaxation, is spatially
characterized by an anisotropy of the zero temperature residual relaxation
only.Comment: Presented at NanoRes 2004, Kazan; 4 pages, 3 Figure
Anisotropic electron spin resonance of YbIr2Si2
A series of electron spin resonance (ESR) experiments were performed on a
single crystal of the heavy fermion metal YbIr2Si2 to map out the anisotropy of
the ESR-intensity I_ESR which is governed by the microwave field component of
the g-factor. The temperature dependencies of I_ESR(T) and g(T) were measured
for different orientations and compared within the range 2.6K \le T \le 16K.
The analysis of the intensity dependence on the crystal orientation with
respect to both the direction of the microwave field and the static magnetic
field revealed remarkable features: The intensity variation with respect to the
direction of the microwave field was found to be one order of magnitude smaller
than expected from the g-factor anisotropy. Furthermore, we observed a weak
basal plane anisotropy of the ESR parameters which we interpret to be an
intrinsic sample property.Comment: 10 pages, 5 figure
Magnetic susceptibility of YbRh2Si2 and YbIr2Si2 on the basis of a localized 4f electron approach
We consider the local properties of the Yb3+ ion in the crystal electric
field in the Kondo lattice compounds YbRh2Si2 and YbIr2Si2. On this basis we
have calculated the magnetic susceptibility taking into account the Kondo
interaction in the simplest molecular field approximation. The resulting
Curie-Weiss law and Van Vleck susceptibilities could be excellently fitted to
experimental results in a wide temperature interval where thermodynamic and
transport properties show non-Fermi-liquid behaviour for these materials.Comment: 12 pages, 4 figures, 4 table
ESR of YbRh2Si2 and 174YbRh2Si2 : local and itinerant properties
Below the Kondo temperature the heavy Fermion compound YbRhSi
shows a well defined Electron Spin Resonance (ESR) with local Yb
properties. We report a detailed analysis of the ESR intensity which gives
information on the number of ESR active centers relative to the ESR of well
localized Yb in YPd:Yb. The ESR lineshape is investigated regarding
contributions from itinerant centers. From the ESR of monoisotopic
YbRhSi we could exclude unresolved hyperfine contributions
to the lineshape.Comment: 3 Figure
Why could Electron Spin Resonance be observed in a heavy fermion Kondo lattice?
We develop a theoretical basis for understanding the spin relaxation
processes in Kondo lattice systems with heavy fermions as experimentally
observed by electron spin resonance (ESR). The Kondo effect leads to a common
energy scale that regulates a logarithmic divergence of different spin kinetic
coefficients and supports a collective spin motion of the Kondo ions with
conduction electrons. We find that the relaxation rate of a collective spin
mode is greatly reduced due to a mutual cancelation of all the divergent
contributions even in the case of the strongly anisotropic Kondo interaction.
The contribution to the ESR linewidth caused by the local magnetic field
distribution is subject to motional narrowing supported by ferromagnetic
correlations. The developed theoretical model successfully explains the ESR
data of YbRh2Si2 in terms of their dependence on temperature and magnetic
field.Comment: 5pages, 1 Figur
Electron Spin Resonance of the ferromagnetic Kondo lattice CeRuPO
The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated
by Electron Spin Resonance (ESR) at microwave frequencies of 1, 9.4, and
34~GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+
resonance in a metallic Ce compound and can be followed below the ferromagnetic
transition temperature Tc=14 K. At T>Tc the interplay between the RKKY-exchange
interaction and the crystal electric field anisotropy determines the ESR
parameters. Near Tc the spin relaxation rate is influenced by the critical
fluctuations of the order parameter.Comment: This is an article accepted for publication in Journal of Physics:
Condensed Matte
Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br: quest for intrinsic scattering contributions
Resistivity measurements have been performed on a low (LR)- and high
(HR)-resistance variant of the kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br superconductor.
While the HR sample was synthesized following the standard procedure, the LR
crystal is a result of a somewhat modified synthesis route. According to their
residual resistivities and residual resistivity ratios, the LR crystal is of
distinctly superior quality. He-gas pressure was used to study the effect of
hydrostatic pressure on the different transport regimes for both variants. The
main results of these comparative investigations are (i) a significant part of
the inelastic-scattering contribution, which causes the anomalous rho(T)
maximum in standard HR crystals around 90 K, is sample dependent, i.e.
extrinsic in nature, (ii) the abrupt change in rho(T) at T* approx. 40 K from a
strongly temperature-dependent behavior at T > T* to an only weakly T-dependent
rho(T) at T < T* is unaffected by this scattering contribution and thus marks
an independent property, most likely a second-order phase transition, (iii)
both variants reveal a rho(T) proportional to AT^2 dependence at low
temperatures, i.e. for T_c < T < T_0, although with strongly sample-dependent
coefficients A and upper bounds for the T^2 behavior measured by T_0. The
latter result is inconsistent with the T^2 dependence originating from coherent
Fermi-liquid excitations.Comment: 8 pages, 6 figure
Evolution of the Kondo state of YbRh2Si2 probed by high field ESR
An electron spin resonance (ESR) study of the heavy fermion compound YbRh2Si2
for fields up to ~ 8 T reveals a strongly anisotropic signal below the single
ion Kondo temperature T_K ~ 25 K. A remarkable similarity between the
T-dependence of the ESR parameters and that of the specific heat and the 29Si
nuclear magnetic resonance data gives evidence that the ESR response is given
by heavy fermions which are formed below T_K and that ESR properties are
determined by their field dependent mass and lifetime. The signal anisotropy,
otherwise typical for Yb{3+} ions, suggests that, owing to a strong
hybridization with conduction electrons at T < T_K, the magnetic anisotropy of
the 4f states is absorbed in the ESR of heavy quasiparticles. Tuning the Kondo
effect on the 4f states with magnetic fields ~ 2 - 8 T and temperature 2 - 25 K
yields a gradual change of the ESR g-factor and linewidth which reflects the
evolution of the Kondo state in this Kondo lattice system.Comment: new substantially revised versio
Why could electron spin resonance be observed in a heavy fermion Kondo lattice?
We develop a theoretical basis for understanding the spin relaxation processes in Kondo lattice systems with heavy fermions as experimentally observed by electron spin resonance (ESR). The Kondo effect leads to a common energy scale that regulates a logarithmic divergence of different spin kinetic coefficients and supports a collective spin motion of the Kondo ions with conduction electrons. We find that the relaxation rate of a collective spin mode is greatly reduced due to a mutual cancellation of all the divergent contributions even in the case of the strongly anisotropic Kondo interaction. The contribution to the ESR linewidth caused by the local magnetic field distribution is subject to motional narrowing supported by ferromagnetic correlations. The developed theoretical model successfully explains the ESR data of YbRh 2Si 2 in terms of their dependence on temperature and magnetic field. © 2009 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg
Low temperature properties of the Electron Spin Resonance in YbRh2Si2
We present the field and temperature behavior of the narrow Electron Spin
Resonance (ESR) response in YbRh2Si2 well below the single ion Kondo
temperature. The ESR g factor reflects a Kondo-like field and temperature
evolution of the Yb3+ magnetism. Measurements towards low temperatures (>0.5K)
have shown distinct crossover anomalies of the ESR parameters upon approaching
the regime of a well defined heavy Fermi liquid. Comparison with the field
dependence of specific heat and electrical resistivity reveal that the ESR
parameters can be related to quasiparticle mass and cross section and, hence,
contain inherent heavy electron properties.Comment: 4 pages, 6 figures; Manuscript for Proceedings of the International
Conference on Quantum Criticality and Novel Phases (QCNP09, Dresden); subm.
to pss(b