280 research outputs found
Anomalous lattice expansion of RuSr2Eu1.5Ce0.5Cu2O10(Ru-1222) magneto superconductor: A low temperature X-ray diffraction study
This is the first report of the observation of the onset of excess volume and
also of the strain along the a-axis near the magnetic ordering temperature in
Ru-1222 superconductor, and indicates a coupling between the lattice and the
magnetism in this system. Magnetization, magneto transport and thermoelectric
power measurements being carried out on the same sample are also reported.Comment: 15 Pages Text Plus Figs. Physica C (2006) accepte
Metal-to-insulator transition and magnetic ordering in CaRu_{1-x}Cu_xO_3
CaRuO_3 is perovskite with an orthorhombic distortion and is believed to be
close to magnetic ordering. Magnetic studies of single crystal and
polycrystalline CaRu_{1-x}Cu_xO_3 (0\le x \le 15 at.%Cu) reveal that
spin-glass-like transition develops for x\le 7 at.%Cu and obtained value for
effective magnetic moment p_{eff}=3.55 mu_B for x=5 at.% Cu, single crystal,
indicates presence of Ru^{5+}. At higher Cu concentrations more complex
magnetic behaviors are observed. Electrical resistivity measured on
polycrystalline samples shows metal-to-insulator transition (MIT) at 51 K for
only 2 at.% Cu. Charge compensation, which is assumed to be present upon
Cu^{2+/3+} substitution, induces appearance of Ru^{5+} and/or creation of
oxygen vacancies in crystal structure. Since the observed changes in physical
properties are completely attributable to the charge compensation, they cannot
be related to behaviors of pure compound where no such mechanism is present.
This study provides the criterion for "good" chemical probes for studying
Ru-based perovskites.Comment: 12 pages, 7 figure
The low-frequency response in the surface superconducting state of ZrB single crystal}
The large nonlinear response of a single crystal ZrB to an ac field
(frequency 40 - 2500 Hz) for has been observed. Direct
measurements of the ac wave form and the exact numerical solution of the
Ginzburg-Landau equations, as well as phenomenological relaxation equation,
permit the study of the surface superconducting states dynamics. It is shown,
that the low frequency response is defined by transitions between the
metastable superconducting states under the action of an ac field. The
relaxation rate which determines such transitions dynamics, is found.Comment: 7 pages, 11 figure
Ruthenocuprates RuSr2(Eu,Ce)2Cu2O10: Intrinsic magnetic multilayers
We report ac susceptibility data on RuSr_2(Eu,Ce)_2Cu_2O_(10-y) (Ru-1222, Ce
content x=0.5 and 1.0), RuSr_2GdCu_2O_8 (Ru-1212) and SrRuO_3. Both Ru-1222
(x=0.5, 1.0) sample types exhibit unexpected magnetic dynamics in low magnetic
fields: logarithmic time relaxation, switching behavior, and `inverted'
hysteresis loops. Neither Ru-1212 nor SrRuO_3 exhibit such magnetic dynamics.
The results are interpreted as evidence of the complex magnetic order in
Ru-1222. We propose a specific multilayer model to explain the data, and note
that superconductivity in the ruthenocuprate is compatible with both the
presence and absence of the magnetic dynamics.Comment: 9 pages, 11 figures, Revtex; submitted to Phys.Rev.
Characteristic crossing point ( K) in specific-heat curves of samples RuSrGdCeCuO taken for different values of magnetic field
Magnetic properties of polycrystalline samples of
RuSr(GdCe)CuO, as-prepared (by
solid-state reaction) and annealed (12 hours at 845C) in pure oxygen
at different pressure (30, 62 and 78 atm) are presented. Specific heat and
magnetization were investigated in the temperature range 1.8--300 K with a
magnetic field up to 8 T. Specific heat, , shows a jump at the
superconducting transition (with onset at K). Below 20 K, a
Schottky-type anomaly becomes apparent in . This low-temperature anomaly
can be attributed to splitting of the ground term of paramagnetic
Gd ions by internal and external magnetic fields. It is found that
curves taken for different values of magnetic field have the same
crossing point (at K) for all samples studied. At the
same time, curves taken for different temperatures have a crossing point
at a characteristic field T. These effects can be
considered as manifestation of the crossing-point phenomenon which is supposed
to be inherent for strongly correlated electron systems.Comment: 10 pages, 7 figures, submitted to J. Phys.: Condens. Matte
Synthesis, Characterization, and Magnetic Properties of gamma-NaxCoO2 (0.70 < x <0.84)
Powder NaCoO () samples were synthesized and
characterized carefully by X-ray diffraction analysis, inductive-coupled plasma
atomic emission spectroscopy, and redox titration. It was proved that
-NaCoO is formed only in the narrow range of . Nevertheless, the magnetic properties depend strongly on . We
found, for the first time, two characteristic features in the magnetic
susceptibility of NaCoO, a sharp peak at K and an
anomaly at K, as well as the transition at K and the broad
maximum at K which had already been reported. A type of weak
ferromagnetic transition seems to occur at . The transition at ,
which is believed to be caused by spin density wave formation, was observed
clearly for with constant and independent of .
On the other hand, ferromagnetic moment varies systematically depending on .
These facts suggest the occurrence of a phase separation at the microscopic
level, such as the separation into Na-rich and Na-poor domains due to the
segregation of Na ions. The magnetic phase diagram and transition mechanism
proposed previously should be reconsidered.Comment: 4 pages (2 figures included) and 2 extra figures (gif), to be
published in J. Phys. Soc. Jpn. 73 (8) with possible minor revision
Heavy quasiparticles in the ferromagnetic superconductor ZrZn2
We report a study of the de Haas-van Alphen effect in the normal state of the
ferromagnetic superconductor ZrZn2. Our results are generally consistent with
an LMTO band structure calculation which predicts four exchange-split Fermi
surface sheets. Quasiparticle effective masses are enhanced by a factor of
about 4.9 implying a strong coupling to magnetic excitations or phonons. Our
measurements provide insight in to the mechanism for superconductivity and
unusual thermodynamic properties of ZrZn2.Comment: 5 pages, 2 figures (one color
Absence of Meissner State and Robust Ferromagnetism in the Superconducting State of UCoGe: Possible Evidence of Spontaneous Vortex State
We report ac magnetic susceptibility and dc magnetization measurements on the
superconducting ferromagnet UCoGe (with superconducting and Curie temperatures
of ~K and ~K, respectively).
In the normal, ferromagnetic state (), the
magnetization curve exhibits a hysteresis loop similar to that of a regular
itinerant ferromagnet. Upon lowering the temperature below , the
spontaneous magnetization is unchanged, but the hysteresis is markedly
enhanced. Even deeply inside the superconducting state, ferromagnetism is not
completely shielded, and there is no Meissner region, a magnetic field region
of (a lower critical field). From these results, we suggest
that UCoGe is the first material in which ferromagnetism robustly survives in
the superconducting state and a spontaneous vortex state without the Meissner
state is realized.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp
Optical study of the electronic phase transition of strongly correlated YbInCu_4
Infrared, visible and near-UV reflectivity measurements are used to obtain
conductivity as a function of temperature and frequency in YbInCu_4, which
exhibits an isostructural phase-transition into a mixed-valent phase below
T_v=42 K. In addition to a gradual loss of spectral weight with decreasing
temperature extending up to 1.5 eV, a sharp resonance appears at 0.25 eV in the
mixed-valent phase. This feature can be described in terms of excitations into
the Kondo (Abrikosov-Suhl) resonance, and, like the sudden reduction of
resistivity, provides a direct reflection of the onset of coherence in this
strongly correlated electron system.Comment: 4 pages, 3 figures (to appear in Phys. Rev. B
Electronic States and Superconducting Transition Temperature based on the Tomonaga-Luttinger liquid in PrBaCuO
An NQR experiment revealed superconductivity of
PrBaCuO (Pr247) to be realized on CuO double chain
layers and suggests possibility of novel one-dimensional(1D) superconductivity.
To clarify the nature of the 1D superconductivity, we calculate the band
dispersions of Pr247 by using the generalized gradient approximation(GGA). It
indicates that Fermi surface of CuO double chains is well described to the
electronic structure of a quasi-1D system.
Assuming the zigzag Hubbard chain model to be an effective model of the
system, we derive tight binding parameters of the model from a fit to the
result of GGA. Based on the Tomonaga-Luttinger liquid theory, we estimate
transition temperature () of the quasi-1D zigzag Hubbard model from the
calculated value of the Luttinger liquid parameter . The result of
is consistent with that of experiments in Pr247 and it suggests that the
mechanism of the superconductivity is well understood within the concept of the
Tomonaga-Luttinger liquid.Comment: 4 pages, 5 figure
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