64 research outputs found
Influence of charging energy on cooper pair tunneling in Bi-2212 small intrinsic Josephson junctions
La impurity effects on quadrupolar ordering in PrPb3
We study low-temperature properties of Pr1-xLaxPb3 with the ground state of a non-Kramers ホ・sub>3 for 0<~x<~0.8. From the concentration dependence of the specific heat, quadrupolar ordering is expected to occur only up to x竏シ0.02. For a wide range of La concentrations where the ordering is absent, the specific heat shows a T linear variation, which is in an excellent agreement with the result obtained by the model for amorphous materials with a random configuration of a two-level system. Impurity effects on quadrupolar moments will be discussed
Specific Heat Study of an S=1/2 Alternating Heisenberg Chain System F_5PNN Under Magnetic Field
We have measured the specific heat of an S=1/2 antiferromagnetic alternating
Heisenberg chain pentafulorophenyl nitronyl nitroxide under magnetic fields up
to H>H_C2. This compound has the field-induced magnetic ordered (FIMO) phase
between H_C1 and H_C2. Characteristic behaviors are observed depending on the
magnetic field up to above H_C2 outside of the H-T boundary for the FIMO.
Temperature and field dependence of the specific heat are qualitatively in good
agreement with the theoretical calculation on an S=1/2 two-leg ladder. [Wang et
al. Phys. Rev. Lett 84 5399 (2000)] This agreement suggests that the observed
behaviors are related with the low-energy excitation in the Tomonaga-Luttinger
liquid.Comment: 4pages, 4figures, replaced with revised version accepted to Physical
Review Letter
Unusual Low-Temperature Phase in VO Nanoparticles
We present a systematic investigation of the crystal and electronic structure
and the magnetic properties above and below the metal-insulator transition of
ball-milled VO nanoparticles and VO microparticles. For this research,
we performed a Rietveld analysis of synchrotron radiation x-ray diffraction
data, O x-ray absorption spectroscopy, V resonant inelastic x-ray
scattering, and magnetic susceptibility measurements. This study reveals an
unusual low-temperature phase that involves the formation of an elongated and
less-tilted V-V pair, a narrowed energy gap, and an induced paramagnetic
contribution from the nanoparticles. We show that the change in the crystal
structure is consistent with the change in the electronic states around the
Fermi level, which leads us to suggest that the Peierls mechanism contributes
to the energy splitting of the state. Furthermore, we find that the
high-temperature rutile structure of the nanoparticles is almost identical to
that of the microparticles.Comment: 7 pages, 8 figures, 2 table
Pressure effects on an S=1 / 2 Heisenberg two-leg ladder antiferromagnet Cu2(C5H12N2)2Cl4
The pressure effects on an S=1/2 Heisenberg two-leg ladder antiferromagnet (H2LLAF) Cu2(C5H12N2)2Cl4 have been investigated through magnetic and thermal measurements under pressures up to 10 kbar. The exchange interactions along the rung and leg hardly change under pressures, but the pressurization induces paramagnetic spins and magnetic order. This magnetic order is a pressure-induced one observed in a quantum spin system with an energy gap. The amount of induced paramagnetic spins increases almost in accordance with the square of pressure. The magnetic field dependence of the pressure-induced Schottky-type heat capacity suggests that the induced paramagnetic spins are not completely free, but weakly correlate with the H2LLAF system. A magnetic anomaly of the heat capacity has been observed around 2.6 K for P>~8.5 kbar, where more than 20% of the paramagnetic spins are induced. This anomaly is considered to be intrinsic to the magnetic order of the H2LLAF system, which seems to be triggered by the modulation of the staggered moment due to local defects. Even below the magnetic ordering temperature, the paramagnetic spins coexit with the magnetic order of the H2LLAF system. These pressure effects are similar to the impurity effects in another typical S=1/2 H2LLAF SrCu2O3 doped with nonmagnetic Zn2+ ions
Pressure effects on an organic radical ferromagnet: 2,5-difluorophenyl-a-nitronyl nitroxide
Raising a transition temperature (Tc) in organic radical ferromagnets is a desire for material scientists. We investigated the pressure effects on an organic radical ferromagnet 2,5-difluorophenyl-α-nitronyl nitroxide (2,5-DFPNN), which has a ferromagnetic transition at 0.45 K. The hydrostatic pressure effects were investigated through measurements of ac magnetic susceptibility (χ) up to P=1.7GPa, heat capacity (Cp) up to P=1.5GPa, and powder x-ray diffraction up to P=4.7GPa. Furthermore, ac magnetic susceptibility under nonhydrostatic pressure was also measured in the pressure region up to 10.0 GPa. As for 2,5-DFPNN, we observed the pressure-induced enhancement of Tc as dTc/dP=7.9×10−2K/GPa [Tc(P=1.5GPa)=0.57K], while other prototypes, the β phase of p-NPNN and p−Cl−C6H4−CH=N−TEMPO show the negative pressure effects. The results for the Cp and the crystal structural analysis suggest that the magnetic dimension of the short-range order developing above Tc transforms from one dimension (a axis) to two dimensions (ac plane) under high pressure. This increase of the magnetic dimension probably promotes to increase Tc. The ferromagnetic signal of χ, however, decreases with increasing pressure, and finally disappears for P>~5.0GPa. The decrease seems to originate from the decrease of the ferromagnetic interaction along the b axis. Similar instability of organic ferromagnetic long range order against pressure has been observed for the β phase of p-NPNN and p−Cl−C6H4−CH=N−TEMPO
Influence of charging energy on Cooper-pair tunneling in Bi-2212 small intrinsic Josephson junctions
We have investigated the properties of submicron intrinsic Josephson junctions (IJJs) fabricated on Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// liquid phase epitaxy film. The IJJs with junction area S<2 /spl mu/m/sup 2/ showed individual current-voltage curves, which have suppressed 1st branch and unsuppressed other branches. This suppression was observed systematically as an increase the ratio of charging energy and Josephson coupling energy. It is expected that such suppressions are due to charging effect in IJJs
Co-existing Singlet and Ordered S=1/2 Moments in the Ground State of the Triclinic Quantum Magnet CuMoO4
CuMoO4 is a triclinic quantum magnet based on S = 1/2 moments at the Cu2+
site. It has recently attracted interest due to the remarkable changes in its
chromic and volumetric properties at high temperatures, and in its magnetic
properties at low temperatures. This material exhibits a first order structural
phase transition at T_C ~ 190 K as well as a magnetic phase transition at T_N ~
1.75 K. We report low temperature heat capacity measurements as well as
extensive elastic and inelastic neutron scattering measurements on powder
samples taken above and below T_N. We observe neutron diffraction consistent
with a simple (1/2, 0, 0) antiferromagnetic structure indicating a doubling of
the a-axis periodicity below T_N. In addition, inelastic neutron scattering
above a spin gap of ~ 2.3 meV is consistent with triplet excitations out of
paired S = 1/2 moments which form singlet dimers. Low lying spin wave
excitations are also observed and these originate from ordered S = 1/2 moments
below T_N. Taken together these measurements show the ground state of CuMoO4 to
display both non-magnetic singlets, and ferromagnetically-coupled spins
coexisting within an antiferromagnetic structure below T_N ~ 1.75 K.Comment: 7 pages, 7 figure
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