10,330 research outputs found
Anomalous Magnetic and Thermal Behavior in Some RMn2O5 Oxides
The RMn2O5 (R=Pr, Nd, Sm, and Eu) oxides showing magnetoelectric (ME)
behavior have been prepared in polycrystalline form by a standard citrate
route. The lattice parameters, obtained from the powder XRD analysis, follow
the rare-earth contraction indicating the trivalent character of the R ions.
Cusp-like anomalies in the magnetic susceptibility curve and sharp peaks in the
specific heat were reported at the corresponding temperatures in RMn2O5 (R=Pr,
Nd, Sm, and Eu) indicating the magnetic or electric ordering transitions.Comment: 2 pages, 1 table, 3 figures, will be published in the Proceedings of
the 24th International Conference on Low Temperature Physic
Experimental evidence for a two-gap structure of superconducting NbSe_2: a specific heat study in external magnetic fields
To resolve the discrepancies of the superconducting order parameter in
quasi-two-dimensional NbSe_2, comprehensive specific-heat measurements have
been carried out. By analyzing both the zero-field and mixed-state data with
magnetic fields perpendicular to and parallel to the c axis of the crystal and
using the two-gap model, we conclude that (1) more than one energy scale of the
order parameter is required for superconducting NbSe_2 due to the thermodynamic
consistency; (2)delta_L=1.26 meV and delta_S=0.73 meV are obtained; (3)
N_S(0)/N(0)=11%~20%; (4) The observation of the kink in gamma(H) curve suggests
that the two-gap scenario is more favorable than the anisotropic s-wave model
to describe the gap structure of NbSe_2; and (5)delta_S is more isotropic and
has a three-dimensional-like feature and is located either on the Se or the
bonding Nb Fermi sheets.Comment: 16 pages, 4 figure
Anomalous pressure effect on the magnetic ordering in multiferroic BiMnO3
We report the magnetic field dependent dc magnetization and the
pressure-dependent (pmax ~ 16 kbar) ac susceptibilities Xp(T) on both powder
and bulk multiferroic BiMnO3 samples, synthesized in different batches under
high pressure. A clear ferromagnetic (FM) transition is observed at TC ~ 100 K,
and increases with magnetic field. The magnetic hysteresis behavior is similar
to that of a soft ferromagnet. Ac susceptibility data indicate that both the FM
peak and its temperature (TC) decrease simultaneously with increasing pressure.
Interestingly, above a certain pressure (9 ~ 11 kbar), another peak appears at
Tp ~ 93 K, which also decreases with increasing pressure, with both these peaks
persisting over some intermediate pressure range (9 ~ 13 kbar). The FM peak
disappears with further application of pressure; however, the second peak
survives until present pressure limit (pmax ~ 16 kbar). These features are
considered to originate from the complex interplay of the magnetic and orbital
structure of BiMnO3 being affected by pressure.Comment: 4 pages,4 figures, publised in Physical Review B 78, 092404/200
Coherent States and Modified de Broglie-Bohm Complex Quantum Trajectories
This paper examines the nature of classical correspondence in the case of
coherent states at the level of quantum trajectories. We first show that for a
harmonic oscillator, the coherent state complex quantum trajectories and the
complex classical trajectories are identical to each other. This congruence in
the complex plane, not restricted to high quantum numbers alone, illustrates
that the harmonic oscillator in a coherent state executes classical motion. The
quantum trajectories are those conceived in a modified de Broglie-Bohm scheme
and we note that identical classical and quantum trajectories for coherent
states are obtained only in the present approach. The study is extended to
Gazeau-Klauder and SUSY quantum mechanics-based coherent states of a particle
in an infinite potential well and that in a symmetric Poschl-Teller (PT)
potential by solving for the trajectories numerically. For the coherent state
of the infinite potential well, almost identical classical and quantum
trajectories are obtained whereas for the PT potential, though classical
trajectories are not regained, a periodic motion results as t --> \infty.Comment: More example
Multiple magnetic transitions in multiferroic BiMnO3
The magnetic phase variations under hydrostatic pressure on multiferroic
BiMnO3 have been examined by the dc magnetization [Mg(T)], magnetic hysteresis
[Ueff(H)], and ac susceptibility [X'g(T)]. Three magnetic transitions,
manifested as kinks I, II, and III on the Mg(T)], curves, were identified at
8.7 and 9.4 kbar. With increasing pressure, transition temperatures of kink I
and kink II TkI and TkII tend to decrease, but the temperature of kink III
TkIII showed more complex variation. Under increasing magnetic field, TkI and
TkII increase; however, TkIII decreases. Combining [Mg(T)] curves with Ueff(H)
and X'g(T), more detailed properties of these three kinks would be shown as
follows. Kink I is a long-range soft ferromagnetic transition which occurs at
TkI 100 K under ambient pressure but is suppressed completely at 11.9 kbar.
Kink II emerges at 8.7 kbar along with TkII 93 K which is also long-range soft
ferromagnetic but canted in nature. Kink III, a canted antiferromagnetic
transition, appears at TkIII 72.5 K along with kink II also at 8.7 kbar. The
proposed phase diagrams at ambient pressure, 9.4 and 11.9 kbar show the
different magnetic features of BiMnO3. These findings are believed to result
from the variations in crystal structure influenced by the external pressure.
These results also indicate the common complicatedComment: 6 paages, 5 gifures, published in Physical Review B 80, 184426/200
Bose-Einstein Condensation of Atoms in a Trap
We point out that the local density approximation (LDA) of Oliva is an
adaptation of the Thomas-Fermi method, and is a good approximation when
,
the LDA leads to a quantitative result (14') easily checked by experiments.
Critical remarks are made about the physics of the many body problem in terms
of the scattering length .Comment: 9 pages, latex. one figure, available from author
O NMR Measurements on Superconducting NaCoOHO
An O NMR measurement was performed on nonoriented polycrystalline
NaCoOHO with superconducting (SC) transition
temperature K. A weak temperature dependence was observed in
the Knight shift at the O site (). The spin part of
() is estimated from the plot of against bulk
susceptibility . The decreases in the SC state,
indicative of the decrease in the in-plane component of the spin
susceptibility. The nuclear spin-lattice relaxation rate at the O site
shows a good scaling with at the Co site .
This indicates that the spin fluctuations at the O site originate from the Co
spin dynamics. The relationships between and and between and show the development of
incommensurate fluctuations at {\bf q 0} other than {\bf q 0} below
30 K. A clear indication of ferromagnetic correlations at {\bf q 0} was not
observed from the present O-NMR studies.Comment: 5 pages, 5 figures, to be published in Journal of physical Society of
Japan vol.74, No.
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