21 research outputs found
Momentum-dependent magnon lifetime in the metallic non-collinear triangular antiferromagnet CrB2
Non-collinear magnetic order arises for various reasons in several magnetic
systems and exhibits interesting spin dynamics. Despite its ubiquitous
presence, little is known of how magnons, otherwise stable quasiparticles,
decay in these systems, particularly in metallic magnets. Using inelastic
neutron scattering, we examine the magnetic excitation spectra in a metallic
non-collinear antiferromagnet CrB, in which Cr atoms form a triangular
lattice and display incommensurate magnetic order. Our data show intrinsic
magnon damping and continuum-like excitations that cannot be explained by
linear spin wave theory. The intrinsic magnon linewidth shows
very unusual momentum dependence, which our analysis shows to originate from
the combination of two-magnon decay and the Stoner continuum. By comparing the
theoretical predictions with the experiments, we identify where in the momentum
and energy space one of the two factors becomes more dominant. Our work
constitutes a rare comprehensive study of the spin dynamics in metallic
non-collinear antiferromagnets. It reveals, for the first time, definite
experimental evidence of the higher-order effects in metallic antiferromagnets.Comment: 6 pages, 4 figures, accepted for publication in PR
Rapid suppression of quantum many-body magnetic exciton in doped van der Waals antiferromagnet (Ni,Cd)PS3
The unique discovery of magnetic exciton in van der Waals antiferromagnet
NiPS3 arises between two quantum many-body states of a Zhang-Rice singlet
excited state and a Zhang-Rice triplet ground state. Simultaneously, the
spectral width of photoluminescence originating from this exciton is
exceedingly narrow as 0.4 meV. These extraordinary properties, including the
extreme coherence of the magnetic exciton in NiPS3, beg many questions. We
studied doping effects using Ni1-xCdxPS3 using two experimental techniques and
theoretical studies. Our experimental results show that the magnetic exciton is
drastically suppressed upon a few % Cd doping. All these happen while the width
of the exciton only gradually increases, and the antiferromagnetic ground state
is robust. These results highlight the lattice uniformity's hidden importance
as a prerequisite for coherent magnetic exciton. Finally, an exciting scenario
emerges: the broken charge transfer forbids the otherwise uniform formation of
the coherent magnetic exciton in (Ni,Cd)PS3.Comment: 40 pages, 4 main figures, 13 supporting figures, accepted by Nano
Letter
Antiferromagnetic Kitaev interaction in J_\rm{eff}=1/2 cobalt honeycomb materials NaCoSbO and NaCoTeO
Finding new materials with antiferromagnetic (AFM) Kitaev interaction is an
urgent issue to broaden and enrich the quantum magnetism research
significantly. By carrying out inelastic neutron scattering experiments and
subsequent analysis, we conclude that NaCoSbO and
NaCoTeO are new honeycomb cobalt-based AFM Kitaev systems. The
spin-orbit excitons at 20-28~meV in both compounds strongly supports the idea
that Co ions of both compounds have a spin-orbital entangled
J_\rm{eff}=1/2 state. Furthermore, we found that a generalized
Kitaev-Heisenberg Hamiltonian can well describe the spin-wave excitations of
both compounds with additional 3rd nearest-neighbor interaction. Our best-fit
parameters show large AFM Kitaev terms and off-diagonal symmetric anisotropy
terms of a similar magnitude in both compounds. We should stress that our
parameters' optimized magnetic structures are consistent with the magnetic
structures reported from neutron diffraction studies. Moreover, there is also
the magnon-damping effect at the higher energy part of the spin waves, as
usually observed in other Kitaev magnets. We demonstrate that
NaCoSbO and NaCoTeO are the first experimental
realization of AFM Kitaev magnets based on the systematic studies of the spin
waves and analysis.Comment: 28 pages, 9 figure
Spin-orbit coupling effects on spin-phonon coupling in Cd2Os2O7
Spin-orbit coupling (SOC) is essential in understanding the properties of 5d
transition metal compounds, whose SOC value is large and almost comparable to
other key parameters. Over the past few years, there have been numerous studies
on the SOC-driven effects of the electronic bands, magnetism, and spin-orbit
entanglement for those materials with a large SOC. However, it is less studied
and remains an unsolved problem in how the SOC affects the lattice dynamics.
We, therefore, measured the phonon spectra of 5d pyrochlore Cd2Os2O7 over the
full Brillouin zone to address the question by using inelastic x-ray scattering
(IXS). Our main finding is a visible mode-dependence in the phonon spectra,
measured across the metal-insulator transition at 227 K. We examined the SOC
strength dependence of the lattice dynamics and its spin-phonon (SP) coupling,
with first-principle calculations. Our experimental data taken at 100 K are in
good agreement with the theoretical results obtained with the optimized U = 2.0
eV with SOC. By scaling the SOC strength and the U value in the DFT
calculations, we demonstrate that SOC is more relevant than U to explaining the
observed mode-dependent phonon energy shifts with temperature. Furthermore, the
temperature dependence of the phonon energy can be effectively described by
scaling SOC. Our work provides clear evidence of SOC producing a non-negligible
and essential effect on the lattice dynamics of Cd2Os2O7 and its SP coupling.Comment: 12 pages, 5 figures, accepted for publication at Rapid Communication
in Physical Review
Bond-dependent anisotropy and magnon breakdown in cobalt Kitaev triangular antiferromagnet
The Kitaev model, a honeycomb network of spins with bond-dependent
anisotropic interactions, is a rare example of having a quantum spin liquid
ground state. Although most Kitaev model candidate materials eventually order
magnetically due to inevitable non-Kitaev terms, their bond-dependent
anisotropy manifests in unusual spin dynamics. It has recently been suggested
that bond-dependent anisotropy can stabilise novel magnetic phases and exotic
spin dynamics on the geometrically frustrated triangular lattice. However, few
materials have been identified with simultaneous geometric frustration and
bond-dependent anisotropy. Here, we report a frustrated triangular lattice with
bond-dependent anisotropy in the cobalt-based triangular van der Waals
antiferromagnet CoI2. Its momentum and energy-resolved spin dynamics exhibit
substantial magnon breakdown and complex level repulsion, as measured by
inelastic neutron scattering. A thorough examination of excitations in both the
paramagnetic and magnetically ordered states reveals that the bond-dependent
anisotropy is the origin of the spiral order and the magnon breakdown found in
CoI2. Our result paves the way toward a new research direction for the Kitaev
model with geometrical frustration.Comment: 13 pages, 4 figures, Under revie
Spin wave Hamiltonian and anomalous scattering in NiPS
We report a comprehensive spin wave analysis of the semiconducting honeycomb
van der Waal antiferromagnet NiPS. Using single crystal inelastic neutron
scattering, we map out the full Brillouin zone and fit the observed modes to a
spin wave model with rigorously defined uncertainty. We find that the third
neighbor exchange dominates the Hamiltonian, a feature which we fully
account for by ab-initio density functional theory calculations. We also
quantify the degree to which the three-fold rotation symmetry is broken and
account for the excitations observed in other measurements, yielding a
spin exchange model which is consistent across multiple experimental probes. We
also identify a strongly reduced static ordered moment and reduced low-energy
intensity relative to the linear spin wave calculations, signaling unexplained
features in the magnetism which requires going beyond the linear spin wave
approximation.Comment: 7 pages, 8 figures; 5 pages and 6 additional figures of appendice
Spin texture induced by non-magnetic doping and spin dynamics in 2D triangular lattice antiferromagnet h-Y(Mn,Al)O3
Novel effects induced by nonmagnetic impurities in frustrated magnets and
quantum spin liquid represent a highly nontrivial and interesting problem. A
theoretical proposal of extended modulated spin structures induced by doping of
such magnets, distinct from the well-known skyrmions has attracted significant
interest. Here, we demonstrate that nonmagnetic impurities can produce such
extended spin structures in h-YMnO3, a triangular antiferromagnet with
noncollinear magnetic order. Using inelastic neutron scattering (INS), we
measured the full dynamical structure factor in Al-doped h-YMnO3 and confirmed
the presence of magnon damping with a clear momentum dependence. Our
theoretical calculations can reproduce the key features of the INS data,
supporting the formation of the proposed spin textures. As such, our study
provides the first experimental confirmation of the impurity-induced spin
textures. It offers new insights and understanding of the impurity effects in a
broad class of noncollinear magnetic systems.Comment: 18 pages, 4 figures and supplementary Information. Accepted for
publication in Nature Communication
Tetrahedral triple-Q magnetic ordering and large spontaneous Hall conductivity in the metallic triangular antiferromagnet Co1/3TaS2
The triangular lattice antiferromagnet (TLAF) has been the standard paradigm
of frustrated magnetism for several decades. The most common magnetic ordering
in insulating TLAFs is the 120 structure. However, a new triple-Q chiral
ordering can emerge in metallic TLAFs, representing the short wavelength limit
of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the
first example of tetrahedral triple-Q magnetic ordering with the associated
topological Hall effect (non-zero {\sigma}_{xy}(H=0)). We also present a
theoretical framework that describes the emergence of this magnetic ground
state, which is further supported by the electronic structure measured by
angle-resolved photoemission spectroscopy. Additionally, our measurements of
the inelastic neutron scattering cross section are consistent with the
calculated dynamical structure factor of the tetrahedral triple-Q state.Comment: 23 pages, 4 figures, SI not included. Accepted for publication in
Nature Communication
Spin texture induced by non-magnetic doping and spin dynamics in 2D triangular lattice antiferromagnet h-Y(Mn,Al)O<sub>3</sub>.
The ginsenoside Rg2 downregulates MMP-1 expression in keratinocyte (HaCaT)-conditioned medium-treated human fibroblasts (Hs68)
Abstract Keratinocytes exposed to UVB induce the production of cytokines, which activate fibroblasts and increase the expression of matrix metalloproteinases (MMPs). The increased expression of MMPs leads to connective tissue damage and wrinkle formation, resulting in skin aging. In this study, we used human dermal fibroblasts cultured in UVB-irradiated keratinocyte-conditioned medium (UV CM) to investigate the potential anti-aging effects of the ginsenoside Rg2 on skin. The inhibitory effect of Rg2 on the MMP-1 gene and protein was determined by real-time PCR and ELISA. We also examined the expression levels of proteins in the mitogen-activated protein kinase (MAPK) signaling pathway using western blotting, to elucidate the underlying mechanism of the inhibitory effect of Rg2. Rg2 inhibited MMP-1 mRNA and protein expression in a concentration-dependent manner. We found that Rg2 inhibited the phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) but not that of p38. Therefore, our results suggest that Rg2 is a potential material for the prevention and treatment of photoaging