12,473 research outputs found
Anisotropic magnetization and resistivity of single crystalline RNi1-xBi2+-y (R = La-Nd, Sm, Gd-Dy)
We present a detailed study of RNi1-xBi2+-y (R = La-Nd, Sm, Gd-Dy) single
crystals by measurements of stoichiometry and temperature dependent magnetic
susceptibility, magnetization, and electrical resistivity. This series forms
with partial Ni occupancy as well as a variable Bi occupancy. For R = Ce-Nd,
Sm, Gd-Dy, the RNi1-xBi2+-y compounds show local-moment like behavior and order
antiferromagnetically at low temperatures. Determination of anisotropies as
well as antiferromagnetic ordering temperatures for RNi1-xBi2+-y (R = Ce-Nd,
Sm, Gd-Dy) have been made. Although crystalline samples from this family
exhibit minority, second phase superconductivity at low temperatures associated
with Ni-Bi and Bi contamination, no evidence of bulk superconductivity has been
observed
Physical properties of VTiO (0 x 0.187) single crystals
Free standing, low strain, single crystals of pure and titanium doped
VO were grown out of an excess of VO using high temperature
solution growth techniques. At 340 K, pure VO exhibits a
clear first-order phase transition from a high-temperature paramagnetic
tetragonal phase (R) to a low-temperature non-magnetic monoclinic phase (M1).
With Ti doping, another monoclinic phase (M2) emerges between the R and M1
phases. The phase transition temperature between R and M2 increases with
increasing Ti doping while the transition temperature between M2 and M1
decreases.Comment: 11 pages, 8 figure
Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on physical properties of CaFeAs
We performed systematic studies of the combined effects of
annealing/quenching temperature ({\itshape T}) and T = Ni, Rh
substitution ({\itshape x}) on the physical properties of
Ca(FeT)As. We constructed two-dimensional, {\itshape
T}-{\itshape x} phase diagrams for the low-temperature states for both
substitutions to map out the relations between ground states and compared them
with that of Co-substitution. Ni-substitution, which brings one more extra
electron per substituted atom and suppresses the {\itshape c}-lattice parameter
at roughly the same rate as Co-substitution, leads to a similar parameter range
of antiferromagnetic/orthorhombic in the {\itshape T}-{\itshape x}
space as that found for Co-substitution, but has the parameter range for
superconductivity shrunk (roughly by a factor of two). This result is similar
to what is found when Co- and Ni-substituted BaFeAs are compared.
On the other hand, Rh-substitution, which brings the same amount of extra
electrons as does Co-substitution, but suppresses the {\itshape c}-lattice
parameter more rapidly, has a different phase diagram. The collapsed tetragonal
phase exists much more pervasively, to the exclusion of the normal,
paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic
phase space is noticeably reduced, and the superconducting region is
substantially suppressed, essentially truncated by the collapsed tetragonal
phase. In addition, we found that whereas for Co-substitution there was no
difference between phase diagrams for samples annealed for one or seven days,
for Ni- and Rh- substitutions a second, reversible, effect of annealing was
revealed by seven-day anneals
Non-conventional superconducting fluctuations in Ba(Fe1-xRhx)2As2 iron-based superconductors
We measured the static uniform spin susceptibility of
Ba(FeRh)As iron-based superconductors, over a broad range
of doping () and magnetic fields. At small fields ( 1 kOe) we observed, above the transition temperature , the occurrence
of precursor diamagnetism, which is not ascribable to the Ginzburg-Landau
theory. On the contrary, our data fit a phase fluctuation model, which has been
used to interpret a similar phenomenology occurring in the high- cuprate
superconductors. On the other hand, in presence of strong fields the
unconventional fluctuating diamagnetism is suppressed, whereas 3D fluctuations
are found, in agreement with literature
Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples
Solution growth of single crystals from high temperature solutions often
involves the separation of residual solution from the grown crystals. For many
growths of intermetallic compounds, this separation has historically been
achieved with the use of plugs of silica wool. Whereas this is generally
efficient in a mechanical sense, it leads to a significant contamination of the
decanted liquid with silica fibers. In this paper we present a simple design
for frit-disc alumina crucible sets that has made their use in the growth
single crystals from high temperature solutions both simple and affordable. An
alumina frit-disc allows for the clean separation of the residual liquid from
the solid phase. This allows for the reuse of the decanted liquid, either for
further growth of the same phase, or for subsequent growth of other, related
phases. In this paper we provide examples of the growth of isotopically
substituted TbCd and icosahedral i-Cd quasicrystals, as well as the
separation of (i) the closely related BiRhS and
BiRhS phases and (ii) PrZn and PrZn.Comment: submitted to Philosophical Magazin
Letter from Storrs, Connecticut: UConn basketball is big in central Connecticut, and not just for the university
When the Huskies are in town, bars are crowded, stores are busy, and restaurants flourish.Basketball - Economic aspects ; Economic conditions - Connecticut
Quantum bicriticality in the heavy-fermion metamagnet YbAgGe
Bicritical points, at which two distinct symmetry-broken phases become
simultaneously unstable, are typical for spin-flop metamagnetism.
Interestingly, the heavy-fermion compound YbAgGe also possesses such a
bicritical point (BCP) with a low temperature T_BCP ~ 0.3 K at a magnetic field
of mu_0 H_BCP ~ 4.5 T. In its vicinity, YbAgGe exhibits anomalous behavior that
we attribute to the influence of a quantum bicritical point (QBCP), that is
close in parameter space yet can be reached by tuning T_BCP further to zero.
Using high-resolution measurements of the magnetocaloric effect, we demonstrate
that the magnetic Grueneisen parameter Gamma_H indeed both changes sign and
diverges as required for quantum criticality. Moreover, Gamma_H displays a
characteristic scaling behavior but only on the low-field side, H < H_BCP,
indicating a pronounced asymmetry with respect to the critical field. We
speculate that the small value of T_BCP is related to the geometric frustration
of the Kondo-lattice of YbAgGe.Comment: submitted to PR
The suppression of electron correlations in the collapsed tetragonal phase of CaFe2As2 under ambient pressure demonstrated by 75As NMR-NQR measurements
The static and the dynamic spin correlations in the low temperature collapsed
tetragonal and the high temperature tetragonal phase in CaFe2As2 have been
investigated by 75As nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) measurements.
Through the temperature (T) dependence of the nuclear spin lattice relaxation
rates (1/T1) and the Knight shifts, although stripe-type antiferromagnetic
(AFM) spin correlations are realized in the high temperature tetragonal phase,
no trace of the AFM spin correlations can be found in the non-superconducting,
low temperature, collapsed tetragonal (cT) phase.
Given that there is no magnetic broadening in 75As NMR spectra, together with
the T-independent behavior of magnetic susceptibility (x) and the T dependence
of 1/T1Tx, we conclude that Fe spin correlations are completely quenched
statically and dynamically in the non-superconducting cT phase in CaFe2As2.Comment: 5 pages, 4 figures, submitted to PR
Physical properties of CeGe2-x (x = 0.24) single crystals
We present data on the anisotropic magnetic properties, heat capacity and
transport properties of CeGe2-x (x = 0.24) single crystals. The electronic
coefficient of the heat capacity, gamma ~ 110 mJ/mol K^2, is enhanced; three
magnetic transitions, with critical temperatures of ~ 7 K, ~ 5 K, and ~ 4 K are
observed in thermodynamic and transport measurements. The ground state has a
small ferromagnetic component along the c - axis. Small applied field, below 10
kOe, is enough to bring the material to an apparent saturated paramagnetic
state (with no further metamagnetic transitions up to 55 kOe) with a reduced,
below 1 mu_B, saturated moment
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The binding affinity of human IgG for its high affinity Fc receptor is determined by multiple amino acids in the CH2 domain and is modulated by the hinge region.
A family of chimeric immunoglobulins (Igs) bearing the murine variable region directed against the hapten dansyl linked to human IgG1, -2, -3, and -4 has been characterized with respect to binding to the human high affinity Fc gamma receptor, Fc gamma RI. Chimeric IgG1 and -3 have the highest affinity association (Ka = 10(9) M-1), IgG4 is 10-fold reduced from this level, and IgG2 displays no detectable binding. A series of genetic manipulations was undertaken in which domains from the strongly binding subclass IgG3 were exchanged with domains from the nonbinding subclass IgG2. The subclass of the CH2 domain was found to be critical for determining IgG receptor affinity. In addition, the hinge region was found to modulate the affinity of the IgG for Fc gamma RI, possibly by determining accessibility of Fc gamma RI to the binding site on Fc. A series of amino acid substitutions were engineered into the CH2 domain of IgG3 and IgG4 at sites considered potentially important to Fc receptor binding based on homology comparisons of binding and nonbinding IgG subclasses. Characterization of these mutants has revealed the importance for Fc gamma RI association of two regions of the genetic CH2 domain separated in primary structure by nearly 100 residues. The first of these is the hinge-link or lower hinge regions, in which two residues, Leu (234) and Leu(235) in IgG1 and -3, are critical to high affinity binding. Substitution at either of these sites reduces the IgG association constant by 10-100-fold. The second region that appears to contribute to receptor binding is in a hinge-proximal bend between two beta strands within the CH2 domain, specifically, Pro(331) in IgG1 and -3. As a result of beta sheet formation within this domain, this residue lies within 11 A of the hinge-link region. Substitution at this site reduces the Fc receptor association constant by 10-fold
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