135 research outputs found
Physical and magnetic properties of Ba(FeRu)As single crystals
Single crystals of Ba(FeRu)As, , have been grown
and characterized by structural, magnetic and transport measurements. These
measurements show that the structural/magnetic phase transition found in pure
BaFeAs at 134 K is suppressed monotonically by Ru doping, but, unlike
doping with TM=Co, Ni, Cu, Rh or Pd, the coupled transition seen in the parent
compound does not detectably split into two separate ones. Superconductivity is
stabilized at low temperatures for and continues through the highest
doping levels we report. The superconducting region is dome like, with maximum
T ( K) found around . A phase diagram of temperature
versus doping, based on electrical transport and magnetization measurements,
has been constructed and compared to those of the
Ba(FeTM)As (TM=Co, Ni, Rh, Pd) series as well as to the
temperature-pressure phase diagram for pure BaFeAs. Suppression of the
structural/magnetic phase transition as well as the appearance of
superconductivity is much more gradual in Ru doping, as compared to Co, Ni, Rh
and Pd doping, and appears to have more in common with BaFeAs tuned
with pressure; by plotting and as a function of changes in unit
cell dimensions, we find that changed in the ratio, rather than changes
in , or V, unify the and phase diagrams for BaFeAs
and Ba(FeRu)As respectively.Comment: 16 pages, 10 figure
Decoupling of the superconducting and magnetic (structural) phase transitions in electron-doped BaFe2As2
Study and comparison of over 30 examples of electron doped BaFe2As2 for
transition metal (TM) = Co, Ni, Cu, and (Co/Cu mixtures) have lead to an
understanding that the suppression of the structural/antiferromagnetic phase
transition to low enough temperature in these compounds is a necessary
condition for superconductivity, but not a sufficient one. Whereas the
structural/antiferromagnetic transitions are suppressed by the number of TM
dopant ions (or changes in the c-axis) the superconducting dome exists over a
limited range of values of the number of electrons added by doping (or values
of the {a/c} ratio). By choosing which combination of dopants are used we can
change the relative positions of the upper phase lines and the superconducting
dome, even to the extreme limit of suppressing the upper structural and
magnetic phase transitions without the stabilization of low temperature
superconducting dome
Effects of Co substitution on thermodynamic and transport properties and anisotropic in Ba(FeCo)As single crystals
Single crystalline samples of Ba(FeCo)As with
have been grown and characterized via microscopic, thermodynamic and transport
measurements. With increasing Co substitution, the thermodynamic and transport
signatures of the structural (high temperature tetragonal to low temperature
orthorhombic) and magnetic (high temperature non magnetic to low temperature
antiferromagnetic) transitions are suppressed at a rate of roughly 15 K per
percent Co. In addition, for superconductivity is stabilized,
rising to a maximum of approximately 23 K for and
decreasing for higher values. The phase diagram for
Ba(FeCo)As indicates that either superconductivity can
exist in both low temperature crystallographic phases or that there is a
structural phase separation. Anisotropic, superconducting, upper critical field
data () show a significant and clear change in anisotropy between
samples that have higher temperature structural phase transitions and those
that do not. These data show that the superconductivity is sensitive to the
suppression of the higher temperature phase transition
Distinct order of Gd 4f and Fe 3d moments coexisting in GdFe4Al8
Single crystals of flux-grown tetragonal GdFe4Al8 were characterized by
thermodynamic, transport, and x-ray resonant magnetic scattering measurements.
In addition to antiferromagnetic order at TN ~ 155 K, two low-temperature
transitions at T1 ~ 21 K and T2 ~ 27 K were identified. The Fe moments order at
TN with an incommensurate propagation vector (tau,tau,0) with tau varying
between 0.06 and 0.14 as a function of temperature, and maintain this order
over the entire T<TN range. The Gd 4f moments order below T2 with a
ferromagnetic component mainly out of plane. Below T1, the ferromagnetic
components are confined to the crystallographic plane. Remarkably, at low
temperatures the Fe moments maintain the same modulation as at high
temperatures, but the Gd 4f moments apparently do not follow this modulation.
The magnetic phase diagrams for fields applied in [110] and [001] direction are
presented and possible magnetic structures are discussed.Comment: v2: 14 pages, 12 figures; PRB in prin
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
Physical properties of GdFe2(AlxZn1-x)(20)
The high ferromagnetic ordering temperature of the dilute, rare-earth-bearing, intermetallic compound GdFe2Zn20 has been understood as being the consequence of the Gd3+ moment being embedded in a nearly ferromagnetic Fermi liquid. To test this understanding in detail, single crystals of the pseudoternary series GdFe2(AlxZn1-x)(20) (
Physical and magnetic properties of Ba(Fe1-xMnx)(2)As-2 single crystals
Single crystals of Ba(Fe1−xMnx)2As2, 00.1–0.2. Our measurements show that whereas the structural/magnetic phase transition found in pure BaFe2As2 at 134 K is initially suppressed by Mn substitution, superconductivity is not observed at any substitution level. Although the effect of hydrostatic pressure up to 20 kbar in the parent BaFe2As2 compound is to suppress the structural/magnetic transition at the approximate rate of 0.9 K/kbar, the effects of pressure and Mn substitution in the x=0.102 compound are not cumulative. Phase diagrams of transition temperature versus substitution concentration x based on electrical transport, magnetization, and thermopower measurements have been constructed and compared to those of the Ba(Fe1−xTMx)2As2 (TM= Co and Cr) series
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