114 research outputs found
Magnetically-induced electric polarization in an organo-metallic magnet
The coupling between magnetic order and ferroelectricity has been under
intense investigation in a wide range of transition-metal oxides. The strongest
coupling is obtained in so-called magnetically-induced multiferroics where
ferroelectricity arises directly from magnetic order that breaks inversion
symmetry. However, it has been difficult to find non-oxide based materials in
which these effects occur. Here we present a study of copper dimethyl sulfoxide
dichloride (CDC), an organo-metallic quantum magnet containing Cu
spins, in which electric polarization arises from non-collinear magnetic order.
We show that the electric polarization can be switched in a stunning hysteretic
fashion. Because the magnetic order in CDC is mediated by large organic
molecules, our study shows that magnetoelectric interactions can exist in this
important class of materials, opening the road to designing magnetoelectrics
and multiferroics using large molecules as building blocks. Further, we
demonstrate that CDC undergoes a magnetoelectric quantum phase transition where
both ferroelectric and magnetic order emerge simultaneously as a function of
magnetic field at very low temperatures
Magnetic properties of GdZn (T = Fe, Co) investigated by X-ray diffraction and spectroscopy
We investigate the magnetic and electronic properties of the GdZn
( = Fe and Co) compounds using X-ray resonant magnetic scattering (XRMS),
X-ray absorption near-edge structure (XANES) and X-ray magnetic circular
dichroism (XMCD) techniques. The XRMS measurements reveal that the
GdCoZn compound has a commensurate antiferromagnetic spin structure
with a magnetic propagation vector =
below the N\'eel temperature ( 5.7 K). Only the Gd ions carry a magnetic moment forming an
antiferromagnetic structure with magnetic representation . For the
ferromagnetic GdFeZn compound, an extensive investigation was
performed at low temperature and under magnetic field using XANES and XMCD
techniques. A strong XMCD signal of about 12.5 and 9.7 is observed
below the Curie temperature ( 85 K) at the Gd- and edges,
respectively. In addition, a small magnetic signal of about 0.06 of the
jump is recorded at the Zn -edge suggesting that the Zn 4 states are spin
polarized by the Gd 5 extended orbitals
High-magnetic field lattice length changes in URu2Si2
We report high magnetic field (up to 45 T) c-axis thermal expansion and
magnetostriction experiments on URu2Si2 single crystals. The sample length
change associated with the transition to the hidden order phase becomes
increasingly discontinous as the magnetic field is raised above 25 T. The
re-entrant ordered phase III is clearly observed in both the thermal expansion
and magnetostriction above 36 T, in good agreement with previous results. The
sample length is also discontinuous at the boundaries of this phase, mainly at
the upper boundary. A change in the sign of the coefficient of
thermal-expansion is observed at the metamagnetic transition (B_M = 38 T) which
is likely related to the existence of a quantum critical end point.Comment: 5 pages, 4 figures, to be published in PR
Origin of the high Seebeck coefficient of the misfit [CaCoO][CoO] cobaltate from site-specific valency and spin-state determinations
Layered misfit cobaltate [CaCoO][CoO], which emerged as
an important thermoelectric material~[A. C. Masset et al. Phys. Rev. B, 62, 166
(2000)], has been explored extensively in the last decade for the exact
mechanism behind its high Seebeck coefficient. Its complex crystal and
electronic structures have inhibited consensus among such investigations. This
situation has arisen mainly due to difficulties in accurate identification of
the chemical state, spin state, and site symmetries in its two subsystems
(rocksalt [CaCoO] and triangular [CoO]). By employing resonant
photoemission spectroscopy and x-ray absorption spectroscopy along with charge
transfer multiplet simulations (at the Co ions), we have successfully
identified the site symmetries, valencies and spin states of the Co in both
layers. Our site-symmetry observations explain the experimental value of the
high Seebeck coefficient and also confirm that the carriers hop within the
rocksalt layer, which is in contrast to earlier reports where hopping within
triangular CoO layer has been held responsible for the large Seebeck
coefficient.Comment: 5 pages, 4 figures and 1 supplementary with 3 figure
Magnetic Properties Of Gdt2zn20 (t=fe, Co) Investigated By X-ray Diffraction And Spectroscopy
We investigate the magnetic and electronic properties of the GdT2Zn20 (T=Fe and Co) compounds using x-ray resonant magnetic scattering (XRMS), x-ray absorption near-edge structure (XANES), and x-ray magnetic circular dichroism (XMCD). The XRMS measurements reveal that GdCo2Zn20 has a commensurate antiferromagnetic spin structure with a magnetic propagation vector τ - =(12,12,12) below the Néel temperature (TN∼5.7 K). Only the Gd ions carry a magnetic moment forming an antiferromagnetic structure with magnetic representation Γ6. For the ferromagnetic GdFe2Zn20 compound, an extensive investigation was performed at low temperature and under magnetic field using XANES and XMCD. A strong XMCD signal of about 12.5% and 9.7% is observed below the Curie temperature (TC∼85K) at the Gd L2 and L3 edges, respectively. In addition, a small magnetic signal of about 0.06% of the jump is recorded at the Zn K edge, suggesting that the Zn 4p states are spin polarized by the Gd 5d extended orbitals. © 2016 American Physical Society.93
Magnetic and orbital correlations in multiferroic CaMnO probed by x-ray resonant elastic scattering
The quadruple perovskite CaMnO is a topical multiferroic, in which
the hierarchy of electronic correlations driving structural distortions,
modulated magnetism, and orbital order is not well known and may vary with
temperature. x-ray resonant elastic scattering (XRES) provides a
momentum-resolved tool to study these phenomena, even in very small single
crystals, with valuable information encoded in its polarization- and
energy-dependence. We present an application of this technique to
CaMnO. By polarization analysis, it is possible to distinguish
superstructure reflections associated with magnetic order and orbital order.
Given the high momentum resolution, we resolve a previously unknown splitting
of an orbital order superstructure peak, associated with a distinct
\textit{locked-in} phase at low temperatures. A second set of orbital order
superstructure peaks can then be interpreted as a second-harmonic orbital
signal. Surprisingly, the intensities of the first- and second-harmonic orbital
signal show disparate temperature and polarization dependence. This orbital
re-ordering may be driven by an exchange mechanism, that becomes dominant over
the Jahn-Teller instability at low temperature.Comment: 6 pages, 4 figures and 1 supplementary with 3 figure
Ferromagnetic Kitaev interaction and the origin of large magnetic anisotropy in -RuCl
-RuCl is drawing much attention as a promising candidate Kitaev
quantum spin liquid. However, despite intensive research efforts, controversy
remains about the form of the basic interactions governing the physics of this
material. Even the sign of the Kitaev interaction (the bond-dependent
anisotropic interaction responsible for Kitaev physics) is still under debate,
with conflicting results from theoretical and experimental studies. The
significance of the symmetric off-diagonal exchange interaction (referred to as
the term) is another contentious question. Here, we present resonant
elastic x-ray scattering data that provides unambiguous experimental
constraints to the two leading terms in the magnetic interaction Hamiltonian.
We show that the Kitaev interaction () is ferromagnetic, and that the
term is antiferromagnetic and comparable in size to the Kitaev
interaction. Our findings also provide a natural explanation for the large
anisotropy of the magnetic susceptibility in -RuCl as arising from
the large term. We therefore provide a crucial foundation for
understanding the interactions underpinning the exotic magnetic behaviours
observed in -RuCl.Comment: 5 pages, two-column, 3 figure
Single-crystal X-ray diffraction and resonant X-ray magnetic scattering at helium-3 temperatures in high magnetic fields at beamline P09 at PETRA III
The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14 T vertical field split-pair magnet. A helium-3 refrigerator is available that can be fitted inside the magnet\u27s variable-temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He-3 insert are presented. By measuring the tetragonal-to-orthorhombic phase transition occurring at 2.1 K in the Jahn-Teller compound TmVO4, it is found that the photon flux at P09 must be attenuated down to 1.5 × 109 photons s-1 for the sample to remain at temperatures below 800 mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X-ray magnetic scattering signal at the Tm LIII absorption edge associated with the spin-density wave in TmNi2B2C below 1.5 K is intense enough to permit a complete study in magnetic field and at sub-Kelvin temperatures to be carried out
Spin waves and spin-state transitions in a ruthenate high-temperature antiferromagnet
Ruthenium compounds play prominent roles in materials research ranging from
oxide electronics to catalysis, and serve as a platform for fundamental
concepts such as spin-triplet superconductivity, Kitaev spin-liquids, and
solid-state analogues of the Higgs mode in particle physics. However, basic
questions about the electronic structure of ruthenates remain unanswered,
because several key parameters (including the Hund's-rule, spin-orbit, and
exchange interactions) are comparable in magnitude, and their interplay is
poorly understood - partly due to difficulties in synthesizing sizable single
crystals for spectroscopic experiments. Here we introduce a resonant inelastic
x-ray scattering (RIXS) technique capable of probing collective modes in
microcrystals of -electron materials. We present a comprehensive set of
data on spin waves and spin-state transitions in the honeycomb antiferromagnet
SrRuO, which possesses an unusually high N\'eel temperature. The
new RIXS method provides fresh insight into the unconventional magnetism of
SrRuO, and enables momentum-resolved spectroscopy of a large class
of transition-metal compounds.Comment: The original submitted version of the published manuscript.
https://www.nature.com/articles/s41563-019-0327-
- …