17,657 research outputs found
Thin radiating shock layer about a blunt body
Boundary layer flow in thin shock layer about axisymmetric blunt bodies studied by Blasius type series expansion techniqu
Neutron scattering study of novel magnetic order in Na0.5CoO2
We report polarized and unpolarized neutron scattering measurements of the
magnetic order in single crystals of Na0.5CoO2. Our data indicate that below
T_N=88 K the spins form a novel antiferromagnetic pattern within the CoO2
planes, consisting of alternating rows of ordered and non-ordered Co ions. The
domains of magnetic order are closely coupled to the domains of Na ion order,
consistent with such a two-fold symmetric spin arrangement. Magnetoresistance
and anisotropic susceptibility measurements further support this model for the
electronic ground state.Comment: 4 pages, 4 figure
Magnetic susceptibility study of hydrated and non-hydrated NaxCoO2-yH2O single crystals
We have measured the magnetic susceptibility of single crystal samples of
non-hydrated NaxCoO2 (x ~ 0.75, 0.67, 0.5, and 0.3) and hydrated Na0.3CoO2-yH2O
(y ~ 0, 0.6, 1.3). Our measurements reveal considerable anisotropy between the
susceptibilities with H||c and H||ab. The derived anisotropic g-factor ratio
(g_ab/g_c) decreases significantly as the composition is changed from the
Curie-Weiss metal with x = 0.75 to the paramagnetic metal with x = 0.3. Fully
hydrated Na0.3CoO2-1.3H2O samples have a larger susceptibility than
non-hydrated Na0.3CoO2 samples, as well as a higher degree of anisotropy. In
addition, the fully hydrated compound contains a small additional fraction of
anisotropic localized spins.Comment: 6 pages, 5 figure
Unique gap structure and symmetry of the charge density wave in single-layer VSe
Single layers of transition metal dichalcogenides (TMDCs) are excellent
candidates for electronic applications beyond the graphene platform; many of
them exhibit novel properties including charge density waves (CDWs) and
magnetic ordering. CDWs in these single layers are generally a planar
projection of the corresponding bulk CDWs because of the quasi-two-dimensional
nature of TMDCs; a different CDW symmetry is unexpected. We report herein the
successful creation of pristine single-layer VSe, which shows a () CDW in contrast to the (4 4) CDW for the layers in
bulk VSe. Angle-resolved photoemission spectroscopy (ARPES) from the single
layer shows a sizable () CDW gap of 100 meV at the
zone boundary, a 220 K CDW transition temperature twice the bulk value, and no
ferromagnetic exchange splitting as predicted by theory. This robust CDW with
an exotic broken symmetry as the ground state is explained via a
first-principles analysis. The results illustrate a unique CDW phenomenon in
the two-dimensional limit
Searching for Stable Na-ordered Phases in Single Crystal Samples of gamma-NaxCoO2
We report on the preparation and characterization of single crystal gamma
phase NaxCoO2 with 0.25 < x < 0.84 using a non-aqueous electrochemical
chronoamperemetry technique. By carefully mapping the overpotential versus x
(for x < 0.84), we find six distinct stable phases with Na levels corresponding
to x ~ 0.75, 0.71, 0.50, 0.43, 0.33 and 0.25. The composition with x ~0.55
appears to have a critical Na concentration which separates samples with
different magnetic behavior as well as different Na ion diffusion mechanisms.
Chemical analysis of an aged crystal reveals different Na ion diffusion
mechanisms above and below x_c ~ 0.53, where the diffusion process above x_c
has a diffusion coefficient about five times larger than that below x_c. The
series of crystals were studied with X-ray diffraction, susceptibility, and
transport measurements. The crystal with x = 0.5 shows a weak ferromagnetic
transition below T=27 K in addition to the usual transitions at T = 51 K and 88
K. The resistivity of the Curie-Weiss metallic Na0.71CoO2 composition has a
very low residual resistivity, which attests to the high homogeneity of the
crystals prepared by this improved electrochemical method. Our results on the
various stable crystal compositions point to the importance of Na ion ordering
across the phase diagram.Comment: 9 pages, 9 figure
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