209 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
Isothermal Oxidation Behaviour of NiCoCrAlYTa Coatings Produced by HVOF Spraying and Tribometâ„¢ Process
Protective NiCoCrAlYTa coatings are used on gas turbine single crystal superalloy blades to provide environmental resistance. They can be deposited by several processes. In this study, isothermal oxidation behaviour of NiCoCrAlYTa coatings produced by HVOF spraying and Tribomet TM process and deposited on single crystal nickel-based superalloy CMSX-4 were compared between 950 and 1,150°C for several exposure durations. Microstructure and chemical composition of both coatings were examined before and after oxidation testing and quite similar observations were made for both coating processes. The combination of phase and chemical analyses allowed the establishment of an occurrence diagram of phases for both coating processes, according to temperature and duration of exposure. The obtained diagrams seemed similar for both processes. Finally both processes appeared to be equivalent for the protection of CMSX-4 superalloy in isothermal oxidation conditions
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
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
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-
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
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