26 research outputs found
The phase diagram of heavy fermions with Cerium and Europium ions
Doniach phase diagram of heavy fermions with Ce and Eu ions is explained by
the scaling solution of the Anderson model. At high temperatures, where the
rear earth ions behave as nearly independent local moments (LM) the system has
a large paramagnetic entropy and its properties are defined by Kondo
temperature, , where is the external parameter, like pressure or
doping. For a given , the scaling law allows an estimate of the
pressure or doping dependence of the coupling constant which is then used to
find the dependence of the RKKY temperature and N\'eel
temperature on the control parameter. The competition between the
on-site Kondo coupling and the off-site RKKY coupling determines the mechanism
by which the system removes the paramagnetic entropy at low temperatures. The
pressure-induced change of the ground state is explained by the differences in
the functional form of and . Our theoretical results
capture the main features shown by the Doniach diagram of CeRuGe,
CeCu(GeSi or EuCu(GeSi.Comment: 6 pages, 2 figure
Temperature dependence of the magnetic anisotropy of metallic Y-Ba-Cu-O single crystals in the normal phase
The magnetic anisotropy measurements of metallic Y-Ba-Cu-O compounds in the normal phase reveal a temperature-dependent diamagnetic component of the susceptibility that increases with decreasing temperature. The temperature variation of the susceptibility anisotropy and its total change do not seem to be much affected by the presence of the superconductivity at some lower temperature and could not be accounted for by superconducting fluctuations. Rather, the data remind one of the behavior of some quasi-two-dimensional metals with anisotropic Fermi surfaces, reflecting the properties of the low-energy excitations in the normal phase. The anisotropy measurements above the bulk superconducting transition temperature Tc reveal the nonlinear effects, which are due to the onset of superconductivity in disconnected grains. The existence of a two-step transition, typical for granular superconductors, should be taken into consideration if the normal-phase susceptibility data are compared with the theoretical predictions in the vicinity of Tc
Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics
The magnetic susceptibility and susceptibility anisotropy of the quasi-binary
alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration
of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The
experimental results are discussed in terms of t he degenerate
Coqblin-Schrieffer model with a crystalline electric field splitting Delta =
330 K. The properties of the model, obtained by combining the lowest-order
scaling and the pertur bation theory, provide a satisfactory description of the
experimental data down to 30 K. The e xperimental results between 20 K and 2 K
are explained by the exact solution of the Kondo mode l for an effective
doublet.Comment: 11 pages, 13 Postscript figures, 1 tabl
Complex magnetic states of heavy fermion compound CeGe
The intermetallic compound CeGe exhibits unusual magnetic behavior due to the interplay between the Kondo
and the antiferromagnetic coupling. This particular system is interesting because the Kondo temperature is close to
the Néel temperature, resulting in a close competition between the low-temperature interactions, which can be
tuned by means of varying external parameters such as pressure and applied magnetic field. Interestingly, magnetization
measurements up to 12 kbar reveal that the Néel temperature is not affected by pressure. Measurements of
the electrical resistivity, however, show that the sharp upturn appearing below TN is sensitive to pressures up to
15 kbar. This suggests that pressure may change the complex antiferromagnetic spin structure. The validity of an
explanation based on the magnetic superzones seen in the rare earths is discussed here
Magnetic anisotropy and low-frequency dielectric response of weak ferromagnetic phase in k-(BEDT-TTF)
We report a detailed characterization of the magnetism and AC transport
in single crystals of the organic conductor
κ-(BEDT-TTF)2Cu[ N(CN)2] Cl by means of magnetic anisotropy
measurements and low-frequency dielectric spectroscopy. Magnetic anisotropy
obeys Curie-Weiss law with negative Curie-Weiss temperature in the
temperature range 300 K-70 K. An antiferromagnetic transition with
concomitant canted antiferromagnetic state is established at 22 K. A large
hysteresis in the spin-flop transition and magnetic field reversal of the
weak ferromagnetic magnetization are documented for the first time. A broad
dielectric relaxation mode of moderate strength () emerges at 32 K, and weakens with temperature. The mean
relaxation time, much larger than that expected for single-particle
excitations, is thermally activated in a manner similar to the DC
conductivity and saturates below 22 K. These features suggest the origin of
the broad relaxation as an intrinsic property of the weak ferromagnetic
ground state. We propose a charged domain wall in a random ferromagnetic
domain structure as the relaxation entity. We argue that the observed
features might be well described if Dzyaloshinsky-Moriya interaction is
taken into account. A Debye relaxation with similar temperature dependence
was also observed and seems to be related to an additional
ferromagnetic-like, most probably, field-induced phase. We tentatively
associate this phase, whose tiny contribution was sample dependent, with
a Cu2+ magnetic subsystem
Complex magnetic states of the heavy fermion compound CeGe
The intermetallic compound CeGe exhibits unusual magnetic behavior owing to the interplay between Kondo and antiferromagnetic coupling. This system is interesting because the Kondo temperature is close to the Néel temperature, so there is a close competition between the low-temperature interactions, which can be tuned by varying external parameters such as pressure and applied magnetic field. Interestingly, magnetization measurements up to 12 kbar reveal that the Néel temperature is not affected by pressure. Measurements of the electrical resistivity show, however, that the sharp upturn below TN is sensitive to pressures up to 15 kbar. This suggests that pressure may change the complex antiferromagnetic spin structure. The validity of an explanation based on the magnetic superzones seen in the rare earths is discussed here