177 research outputs found
Single crystal growth from light, volatile, and reactive materials using lithium and calcium flux
We present a method for the solution growth of single crystals from reactive
Li and Ca melts and its application to the synthesis of several, representative
compounds. Among these, single crystalline Li3N, Li2(Li{1-x}Tx)N with T = {Mn,
Fe, Co}, LiCaN, Li2C2, LiRh, and LiIr from Li-rich flux as well as Ca2N, CaNi2,
CaNi3, YbNi2, Y2Ni7, and LaNi5 from Ca-rich flux could be obtained. Special
emphasize is given on the growth of nitrides using commercially available Li3N
and Ca3N2 powders as the nitrogen source instead of N2 gas.Comment: 40 pages, 20 figures, reference list update
Single crystal growth and characterization of the large-unit-cell compound Cu13Ba
Single crystals of CuBa were successfully grown out of Ba-Cu self
flux. Temperature dependent magnetization, , electrical resistivity,
, and specific heat, , data are reported. Isothermal
magnetization measurements, , show clear de Haas-van Alphen oscillations
at = 2 K for applied fields as low as = 1T. An anomalous behavior
of the magnetic susceptibility is observed up to ~ 50K reflecting the
effect of de Haas-van Alphen oscillations at fairly high temperatures. The
field- and temperature-dependencies of the magnetization indicate the presence
of diluted magnetic impurities with a concentration of the order of 0.01at.%.
Accordingly, the minimum and lower temperature rise observed in the electrical
resistivity at and below = 15K is attributed to the Kondo impurity effect.Comment: 6 pages, 8 figures, accepted for publication in J. Alloys Comp
Structural trends from a consistent set of single-crystal data of REFeAsO (RE = La, Ce, Pr, Nd, Sm, Gd, and Tb)
A new crystal growth technique for single-crystals of REFeAsO (RE = La, Ce,
Pr, Nd, Sm, Gd, and Tb) using NaI/KI as flux is presented. Crystals with a size
up to 300 m were isolated for single-crystal X-ray diffraction
measurements. Lattice parameters were determined by LeBail fits of X-ray powder
data against LaB6 standard. A consistent set of structural data is obtained and
interpreted in a hard-sphere model. Effective radii for the rare-earth metal
atoms for REFeAsO are deduced. The relation of the intra- and inter-plane
distances of the arsenic atoms is identified as limiter of the phase formation,
and its influence on Tc is discussed.Comment: 8 pages, 11 figures, 3 tables, fig. 6 changed to numerical plot,
minor changes to the text, accepted for publication in PR
Cooperative quantum tunneling of the magnetization in Fe-doped LiN
The spin-reversal in dilute Li(LiFe)N with % is
dominated by resonant quantum tunneling of spatially well-separated states. We
report on the effect of finite couplings between those states that give rise to
cooperative, simultaneous quantum tunneling of two spins. This phenomenon,
known as spin-spin cross relaxation, effectively elucidates the fine-structure
observed in isothermal magnetization loops, a previously unresolved aspect.
Temperature and field-dependent magnetization measurements were conducted over
a range from T = 2 K to 300 K in applied fields of up to = 7 T.
Magnetic dipole fields are computed numerically. Our findings affirm the
absence of stoichiometric defects in Li(LiFe)N and underscore
its exemplary suitability as a model system for investigating spin-reversal
processes at the microscopic level. This is attributed to its comparatively
simple crystal structure, the availability of large single crystals, elevated
characteristic energies, and well-defined energy levelsComment: 7 pages, 4 figure
Structural and magnetic transition in CeFeAsO: separated or connected?
Using an adapted Sn-flux growth technique we obtained comparatively large
CeFeAsO single crystals of better quality than previously reported polycrystals
or single crystals, as evidenced by much sharper anomalies at the structural
and magnetic phase transitions as well as a much higher residual resistivity
ratio of 12. In the magnetically ordered phase we observe a very pronounced
metallic behavior of the in-plane resistivity, which excludes a Mott insulator
regime at low temperature. The separation Delta_T = T_0 - T_N between
structural and magnetic ordering temperatures decreases with increasing sample
quality, from 18 K in the initial reports to 6 K in the present single
crystals, demonstrating that this separation is not an intrinsic property of
the RFeAsO systems. Our results indicate that the coupling between magnetic
ordering and structural distortion is very similar in AFe2As2 and RFeAsO type
of compounds, much more similar than previously thought. The implications of
our experimental results give arguments both in favor and against the nematic
phase model.Comment: published in PRB with the title 'Coupling between the structural and
magnetic transition in CeFeAsO
Ferromagnetic ordering of linearly coordinated Co ions in LiSr[CoN]
LiSr[CoN] single crystals were successfully grown out of Li-rich
flux. Temperature- and field-dependent measurements of the magnetization in the
range of K and up to T as well as
measurements of the heat capacity are presented. Ferromagnetic ordering emerges
below K and comparatively large coercivity fields of
T as well as pronounced anisotropy are observed upon cooling. Polycrystalline
samples of the Ca analog LiCa[CoN] were obtained and investigated in a
similar way. In both compounds Co manifests orbital contributions to the
magnetic moment and large single-ion anisotropy that is caused by second-order
Spin-orbit coupling. Quantum chemistry calculations reveal a magnetic
anisotropy energy of 7 meV, twice as large as the values reported for similar
Co systems.Comment: 21 pages, 6 figures, 5 table
Iron single crystal growth from a lithium-rich melt
\alpha-Fe single crystals of rhombic dodecahedral habit were grown from a
melt of LiNFe. Crystals of several millimeter along a
side form at temperatures around C. Upon further cooling
the growth competes with the formation of Fe-doped LiN. The b.c.c.
structure and good sample quality of \alpha-Fe single crystals were confirmed
by X-ray and electron diffraction as well as magnetization measurements and
chemical analysis. A nitrogen concentration of 90\,ppm was detected by means of
carrier gas hot extraction. Scanning electron microscopy did not reveal any
sign of iron nitride precipitates.Comment: 13 pages, 4 figure
Anisotropic electrical resistivity of LaFeAsO: evidence for electronic nematicity
Single crystals of LaFeAsO were successfully grown out of KI flux.
Temperature dependent electrical resistivity was measured with current flow
along the basal plane, \rho_perpend(T), as well as with current flow along the
crystallographic c-axis, \rho_parallel(T), the latter one utilizing electron
beam lithography and argon ion beam milling. The anisotropy ratio was found to
lie between \rho_parallel/\rho_perpend = 20 - 200. The measurement of
\rho_perpend(T) was performed with current flow along the tetragonal [1 0 0]
direction and along the [1 1 0] direction and revealed a clear in-plane
anisotropy already at T \leq 175 K. This is significantly above the
orthorhombic distortion at T_0 = 147 K and indicates the formation of an
electron nematic phase. Magnetic susceptibility and electrical resistivity give
evidence for a change of the magnetic structure of the iron atoms from
antiferromagnetic to ferromagnetic arrangement along the c-axis at T^\ast = 11
K.Comment: 10 pages, 6 figures, minor change
Avoided ferromagnetic quantum critical point in CeRuPO
CeRuPO is a rare example of a ferromagnetic (FM) Kondo-lattice system.
External pressure suppresses the ordering temperature to zero at about
GPa. Our ac-susceptibility and electrical-resistivity
investigations evidence that the type of magnetic ordering changes from FM to
antiferromagnetic (AFM) at about GPa. Studies in applied
magnetic fields suggest that ferromagnetic and antiferromagnetic correlations
compete for the ground state at , but finally the AFM correlations win.
The change in the magnetic ground-state properties is closely related to the
pressure evolution of the crystalline-electric-field level (CEF) scheme and the
magnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction. The
N\'{e}el temperature disappears abruptly in a first-order-like fashion at
, hinting at the absence of a quantum critical point. This is consistent
with the low-temperature transport properties exhibiting Landau-Fermi-liquid
(LFL) behavior in the whole investigated pressure range up to 7.5 GPa.Comment: 12 figure
Optical signature of the pressure-induced dimerization in the honeycomb iridate -LiIrO
We studied the effect of external pressure on the electrodynamic properties
of -LiIrO single crystals in the frequency range of the phonon
modes and the Ir - transitions. The abrupt hardening of several phonon
modes under pressure supports the onset of the dimerized phase at the critical
pressure =3.8 GPa. With increasing pressure an overall decrease in
spectral weight of the Ir - transitions is found up to . Above
, the local (on-site) - excitations gain spectral weight with
increasing pressure, which hints at a pressure-induced increase in the
octahedral distortions. The non-local (intersite) Ir - transitions show a
monotonic blue-shift and decrease in spectral weight. The changes observed for
the non-local excitations are most prominent well above , namely for
pressures 12 GPa, and only small changes occur for pressures close to
. The profile of the optical conductivity at high pressures (20 GPa)
appears to be indicative for the dimerized state in iridates.Comment: 10 pages, 6 figures; accepted for publication in Phys. Rev.
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