1,643 research outputs found
Magnetic and thermal properties of the S = 1/2 zig-zag spin-chain compound In2VO5
Static magnetic susceptibility \chi, ac susceptibility \chi_{ac} and specific
heat C versus temperature T measurements on polycrystalline samples of In2VO5
and \chi and C versus T measurements on the isostructural, nonmagnetic compound
In2TiO5 are reported. A Curie-Wiess fit to the \chi(T) data above 175 K for
In2VO5 indicates ferromagnetic exchange between V^{4+} (S = 1/2) moments. Below
150 K the \chi(T) data deviate from the Curie-Weiss behavior but there is no
signature of any long range magnetic order down to 1.8 K. There is a cusp at
2.8 K in the zero field cooled (ZFC) \chi(T) data measured in a magnetic field
of 100 Oe and the ZFC and field cooled (FC) data show a bifurcation below this
temperature. The frequency dependence of the \chi_{ac}(T) data indicate that
below 3 K the system is in a spin-glass state. The difference \Delta C between
the heat capacity of In2VO5 and In2TiO5 shows a broad anomaly peaked at 130 K.
The entropy upto 300 K is more than what is expected for S = 1/2 moments. The
anomaly in \Delta C and the extra entropy suggests that there may be a
structural change below 130 K in In2VO5.Comment: 6 pages, 7 figures, 1 tabl
High superconducting anisotropy and weak vortex pinning in Co doped LaFeAsO
Here, we present an electrical transport study in single crystals of
LaFeCoAsO ( K) under high magnetic fields. In
contrast to most of the previously reported Fe based superconductors, and
despite its relatively low , LaFeCoAsO shows a superconducting
anisotropy which is comparable to those seen for instance in the cuprates or
, where
is the effective mass anisotropy. Although, in the present case and as in all
Fe based superconductors, as . Under
the application of an external field, we also observe a remarkable broadening
of the superconducting transition particularly for fields applied along the
inter-planar direction. Both observations indicate that the low dimensionality
of LaFeCoAsO is likely to lead to a more complex vortex
phase-diagram when compared to the other Fe arsenides and consequently, to a
pronounced dissipation associated with the movement of vortices in a possible
vortex liquid phase. When compared to, for instance, F-doped compounds
pertaining to same family, we obtain rather small activation energies for the
motion of vortices. This suggests that the disorder introduced by doping
LaFeAsO with F is more effective in pinning the vortices than alloying it with
Co.Comment: 7 figures, 7 pages, Phys. Rev. B (in press
Low-Temperature Rapid Synthesis and Superconductivity of Fe-Based Oxypnictide Superconductors
we were able to develop a novel method to synthesize Fe-based oxypnictide
superconductors. By using LnAs and FeO as the starting materials and a
ball-milling process prior to solid-state sintering, Tc as high as 50.7 K was
obtained with the sample of Sm 0.85Nd0.15FeAsO0.85F0.15 prepared by sintering
at temperatures as low as 1173 K for times as short as 20 min.Comment: 2 pages,2 figures, 1 tabl
Electrically-detected magnetic resonance in ion-implanted Si:P nanostructures
We present the results of electrically-detected magnetic resonance (EDMR)
experiments on silicon with ion-implanted phosphorus nanostructures, performed
at 5 K. The devices consist of high-dose implanted metallic leads with a square
gap, into which Phosphorus is implanted at a non-metallic dose corresponding to
10^17 cm^-3. By restricting this secondary implant to a 100 nm x 100 nm region,
the EDMR signal from less than 100 donors is detected. This technique provides
a pathway to the study of single donor spins in semiconductors, which is
relevant to a number of proposals for quantum information processing.Comment: 9 pages, 3 figure
Probing fractal magnetic domains on multiple length scales in Nd2Fe14B
Using small-angle neutron scattering, we demonstrate that the complex
magnetic domain patterns at the surface of Nd2Fe14B, revealed by quantitative
Kerr and Faraday microscopy, propagate into the bulk and exhibit structural
features with dimensions down to 6 nm, the domain wall thickness. The observed
fractal nature of the domain structures provides an explanation for the
anomalous increase in the bulk magnetization of Nd2Fe14B below the
spin-reorientation transition. These measurements open up a rich playground for
studies of fractal structures in highly anisotropic magnetic systems.Comment: Accepted for publication in Phys. Rev. Lett. (4 pages, 4 figures
Cation, dipole, and spin order in Pb(Fe2/3W1/3)O3-based magnetoelectric multiferroic compounds
Long range 1:1 cation order was developed in Pb(Fe2(1−x)/3Sc2x/3W1/3)O3solid solution compounds by high temperature solid state reaction. It is found that the degree of cation order directly influences the saturation magnetization in these single phase compounds. A high saturation magnetization (∼0.61μB/f.u.) was observed for x=0.15 at 10Kunder 5T. A ferrimagnetic structure was suggested to take into account for the observed magnetic behavior. These compounds also display a saturated electrical polarization of ∼15μC/cm2 at 40kV/cm at 120K
Interplay between Fe and Nd magnetism in NdFeAsO single crystals
The structural and magnetic phase transitions have been studied on NdFeAsO
single crystals by neutron and x-ray diffraction complemented by resistivity
and specific heat measurements. Two low-temperature phase transitions have been
observed in addition to the tetragonal-to-orthorhombic transition at T_S = 142
K and the onset of antiferromagnetic (AFM) Fe order below T_N = 137 K. The Fe
moments order AFM in the well-known stripe-like structure in the (ab) plane,
but change from AFM to ferromagnetic (FM) arrangement along the c direction
below T* = 15 K accompanied by the onset of Nd AFM order below T_Nd = 6 K with
this same AFM configuration. The iron magnetic order-order transition in
NdFeAsO accentuates the Nd-Fe interaction and the delicate balance of c-axis
exchange couplings that results in AFM in LaFeAsO and FM in CeFeAsO and
PrFeAsO.Comment: revised; 4 pages, 3 figures; accepted for publication in Phys. Rev.
Discovery of a binary icosahedral quasicrystal in ScZn
We report the discovery of a new binary icosahedral phase in a Sc-Zn alloy
obtained through solution-growth, producing millimeter-sized, facetted, single
grain, quasicrystals that exhibit different growth morphologies, pentagonal
dodecahedra and rhombic triacontahedra, under only marginally different growth
conditions. These two morphologies manifest different degrees of
quasicrystalline order, or phason strain. The discovery of i-ScZn
suggests that a reexamination of binary phase diagrams at compositions close to
crystalline approximant structures may reveal other, new binary
quasicrystalline phases.Comment: Incorrect spelling in author list resolve
Magnetism dependent phonon anomaly in LaFeAsO observed via inelastic x-ray scattering
The phonon dispersion was measured at room temperature along (0,0,L) in the
tetragonal phase of LaFeAsO using inelastic x-ray scattering. Spin-polarized
first-principles calculations imposing various types of antiferromagnetic order
are in better agreement with the experimental results than nonmagnetic
calculations, although the measurements were made well above the magnetic
ordering temperature, T_N. Splitting observed between two A_{1g} phonon modes
at 22 and 26 meV is only observed in spin-polarized calculations.
Magneto-structural effects similar to those observed in the AFe_2As_2 materials
are confirmed present in LaFeAsO. The presence of Fe-spin is necessary to find
reasonable agreement of the calculations with the measured spectrum well above
T_N. On-site Fe and As force constants show significant softening compared to
nonmagnetic calculations, however an investigation of the real-space force
constants associates the magnetoelastic coupling with a complex renormalization
instead of softening of a specific pairwise force.Comment: 7 pages, 4 figure
The static quark-antiquark potential in QCD to three loops
The static potential between an infinitely heavy quark and antiquark is
derived in the framework of perturbative QCD to three loops by performing a
full calculation of the two-loop diagrams and using the renormalization group.
The contribution of massless fermions is included.Comment: Latex, 11 pages, 3 figures included. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ . Revised version,
essentially identical to the version published in Physical Review Letter
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