948 research outputs found
Magnetoelectric effects in an organo-metallic quantum magnet
We observe a bilinear magnetic field-induced electric polarization of 50 in single crystals of NiCl-4SC(NH) (DTN). DTN forms a
tetragonal structure that breaks inversion symmetry, with the highly polar
thiourea molecules all tilted in the same direction along the c-axis.
Application of a magnetic field between 2 and 12 T induces canted
antiferromagnetism of the Ni spins and the resulting magnetization closely
tracks the electric polarization. We speculate that the Ni magnetic forces
acting on the soft organic lattice can create significant distortions and
modify the angles of the thiourea molecules, thereby creating a magnetoelectric
effect. This is an example of how magnetoelectric effects can be constructed in
organo-metallic single crystals by combining magnetic ions with electrically
polar organic elements.Comment: 3 pages, 3 figure
Electronic Scattering Effects in Europium-Based Iron Pnictides
In a comprehensive study, we investigate the electronic scattering effects in
EuFe(AsP) by using Fourier-transform infrared
spectroscopy. In spite of the fact that Eu local moments order around
\,K, the overall optical response is strikingly similar
to the one of the well-known Ba-122 pnictides. The main difference lies within
the suppression of the lower spin-density-wave gap feature. By analysing our
spectra with a multi-component model, we find that the high-energy feature
around 0.7\,eV -- often associated with Hund's rule coupling -- is highly
sensitive to the spin-density-wave ordering, this further confirms its direct
relationship to the dynamics of itinerant carriers. The same model is also used
to investigate the in-plane anisotropy of magnetically detwinned
EuFeAs in the antiferromagnetically ordered state, yielding a
higher Drude weight and lower scattering rate along the crystallographic
-axis. Finally, we analyse the development of the room temperature spectra
with isovalent phosphor substitution and highlight changes in the scattering
rate of hole-like carriers induced by a Lifshitz transition
The monoclinic crystal structure of -RuCl and the zigzag antiferromagnetic ground state
The layered honeycomb magnet alpha-RuCl3 has been proposed as a candidate to
realize a Kitaev spin model with strongly frustrated, bond-dependent,
anisotropic interactions between spin-orbit entangled jeff=1/2 Ru4+ magnetic
moments. Here we report a detailed study of the three-dimensional crystal
structure using x-ray diffraction on untwinned crystals combined with
structural relaxation calculations. We consider several models for the stacking
of honeycomb layers and find evidence for a crystal structure with a monoclinic
unit cell corresponding to a stacking of layers with a unidirectional in-plane
offset, with occasional in-plane sliding stacking faults, in contrast with the
currently-assumed trigonal 3-layer stacking periodicity. We report electronic
band structure calculations for the monoclinic structure, which find support
for the applicability of the jeff=1/2 picture once spin orbit coupling and
electron correlations are included. We propose that differences in the
magnitude of anisotropic exchange along symmetry inequivalent bonds in the
monoclinic cell could provide a natural mechanism to explain the spin gap
observed in powder inelastic neutron scattering, in contrast to spin models
based on the three-fold symmetric trigonal structure, which predict a gapless
spectrum within linear spin wave theory. Our susceptibility measurements on
both powders and stacked crystals, as well as neutron powder diffraction show a
single magnetic transition at TN ~ 13K. The analysis of the neutron data
provides evidence for zigzag magnetic order in the honeycomb layers with an
antiferromagnetic stacking between layers. Magnetization measurements on
stacked single crystals in pulsed field up to 60T show a single transition
around 8T for in-plane fields followed by a gradual, asymptotic approach to
magnetization saturation, as characteristic of strongly anisotropic exchange
interactions.Comment: 13 pages, 9 figures, published in Physical Review
Low temperature specific heat of the heavy fermion superconductor PrOsSb
We report the magnetic field dependence of the low temperature specific heat
of single crystals of the first Pr-based heavy fermion superconductor
PrOsSb. The low temperature specific heat and the magnetic phase
diagram inferred from specific heat, resistivity and magnetisation provide
compelling evidence of a doublet ground state and hence superconductivity
mediated by quadrupolar fluctuations. This establishes PrOsSb as a
very strong contender of superconductive pairing that is neither
electron-phonon nor magnetically mediated.Comment: 4 pages, 4 figure
Persistent detwinning of iron pnictides by small magnetic fields
Our comprehensive study on EuFeAs reveals a dramatic reduction of
magnetic detwinning fields compared to other AFeAs (A = Ba, Sr, Ca)
iron pnictides by indirect magneto-elastic coupling of the Eu ions. We
find that only 0.1T are sufficient for persistent detwinning below the local
Eu ordering; above = 19K, higher fields are necessary.
Even after the field is switched off, a significant imbalance of twin domains
remains constant up to the structural and electronic phase transition (190K).
This persistent detwinning provides the unique possibility to study the low
temperature electronic in-plane anisotropy of iron pnictides without applying
any symmetrybreaking external force.Comment: accepted by Physical Review Letter
Superconductivity and crystalline electric field effects in the filled skutterudite series Pr(OsRu)Sb
X-ray powder diffraction, magnetic susceptibility , and electrical
resistivity measurements were made on single crystals of the filled
skutterudite series Pr(OsRu)Sb. One end of the series
() is a heavy fermion superconductor with a superconducting critical
temperature K, while the other end () is a conventional
superconductor with K. The lattice constant decreases
approximately linearly with increasing Ru concentration . As Ru (Os) is
substituted for Os (Ru), decreases nearly linearly with substituent
concentration and exhibits a minimum with a value of K at , suggesting that the two types of superconductivity compete with one
another. Crystalline electric field (CEF) effects in and
due to the splitting of the Pr nine-fold degenerate Hund's
rule multiplet are observed throughout the series, with the splitting
between the ground state and the first excited state increasing monotonically
as increases. The fits to the and data are
consistent with a doublet ground state for all values of x,
although reasonable fits can be obtained for a ground state for
values near the end member compounds ( or ).Comment: 10 pages, 8 figures, submitted to Phys. Rev.
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