56 research outputs found
N\'eel-type skyrmion lattice in tetragonal polar magnet VOSeO
Formation of the triangular skyrmion-lattice is found in a tetragonal polar
magnet VOSeO. By magnetization and small-angle neutron scattering
measurements on the single crystals, we identify a cycloidal spin state at zero
field and a N\'eel-type skyrmion-lattice phase under a magnetic field along the
polar axis. Adjacent to this phase, another magnetic phase of an incommensurate
spin texture is identified at lower temperatures, tentatively assigned to a
square skyrmion-lattice phase. These findings exemplify the versatile features
of N\'eel-type skyrmions in bulk materials, and provide a unique occasion to
explore the physics of topological spin textures in polar magnets.Comment: 11 pages, 4 figures, supplemental material (7 pages
Nonreciprocal second harmonic generation in a magnetoelectric material
Nonreciprocal devices that allow the light propagation in only one direction
are indispensable in photonic circuits and emerging quantum technologies.
Contemporary optical isolators and circulators, however, require large size or
strong magnetic fields because of the general weakness of magnetic light-matter
interactions, which hinders their integration into photonic circuits. Aiming at
stronger magneto-optical couplings, a promising approach is to utilize
nonlinear optical processes. Here, we demonstrate nonreciprocal magnetoelectric
second harmonic generation (SHG) in CuB2O4. SHG transmission changes by almost
100% in a magnetic-field reversal of just 10 mT. The observed nonreciprocity
results from an interference between the magnetic-dipole- and
electric-dipole-type SHG. Even though the former is usually notoriously smaller
than the latter, it is found that a resonantly enhanced
magnetic-dipole-transition has a comparable amplitude as non-resonant
electric-dipole-transition, leading to the near-perfect nonreciprocity. This
mechanism could form one of the fundamental bases of nonreciprocity in
multiferroics, which is transferable to a plethora of magnetoelectric systems
to realize future nonreciprocal and nonlinear-optical devices.Comment: 21 pages, 4 figure
Spin Excitation in Coupled Honeycomb Lattice NiInSbO
We performed an inelastic neutron scattering experiment on a polycrystalline
sample of a helimagnet NiInSbO to construct the spin Hamiltonian.
Well-defined spin-wave excitation with a band energy of 20 meV was observed
below K. Using the linear spin-wave theory, the spectrum was
reasonably reproduced with honeycomb spin layers coupled along the stacking
axis (the axis). The proposed spin model reproduces the soliton lattice
induced by a magnetic field applied perpendicular to the axis.Comment: 8 pages, 5 figure
Anisotropic magnetotransport properties coupled with spiral spin modulation in a triangular-lattice magnet EuZnGe
We investigate the thermodynamic, magnetic, and electrical transport
properties of a triangular-lattice antiferromagnet EuZnGe using single crystals
grown from Eu-Zn flux in sealed tantalum tubes. Magnetic properties are found
to be isotropic in the paramagnetic state while we observe an enhancement of
in-plane magnetic susceptibility at the temperature near T* =11.3 K, suggesting
an easy-plane anisotropy at low temperatures. Magnetic transition temperature
is lower than T* as specific heat shows a peak at TN =7.6 K. We reveal the
magnetic modulation along the c axis by resonant x-ray scattering at Eu L2
edge, which suggests competing magnetic interaction among Eu triangular-lattice
layers. We observe a double-peak structure in the intensity profile along (0,
0, L) below TN, which is mainly composed of a dominant helical modulation with
q ~ (0, 0, 0.4) coexisting with a secondary contribution from q ~ (0, 0, 0.5).
We reproduce the intensity profile with a random mixture of five- and
four-sublattice helices with spin rotation skipping due to hexagonal in-plane
anisotropy. The metallic conductivity is highly anisotropic with the ratio
rho_zz/rho_xx exceeding 10 over the entire temperature range and additionally
exhibits a sharp enhancement of rho_zz at TN giving rise to rho_zz/rho_xx ~ 50,
suggesting a coupling between out-of-plane electron conduction and the spiral
magnetic modulations. In-plane magnetic field induces a spin-flop like
transition, where the q = 0.4 peak disappears and an incommensurate peak of
approximately qICM ~ 0.47 emerges, while the q = 0.5 modulation retains a
finite intensity. This transition correlates with non-monotonic
magnetoresistance and Hall resistivity, suggesting a significant interplay
between electrons and spin structures through Ruderman-Kittel-Kasuya-Yosida
(RKKY) interaction.Comment: 9 pages, 6 figure
Kagome lattice promotes chiral spin fluctuations
Magnetic materials with tilted electron spins often exhibit conducting
behavior that cannot be explained from semiclassical theories without invoking
fictitious (emergent) electromagnetic fields. Quantum-mechanical models
explaining such phenomena are rooted in the concept of a moving quasiparticle's
Berry phase, driven by a chiral (left- or right-handed) spin-habit. Dynamical
and nearly random spin fluctuations, with a slight bent towards left- or
right-handed chirality, represent a promising route to realizing Berry-phase
phenomena at elevated temperatures, but little is known about the effect of
crystal lattice geometry on the resulting macroscopic observables. Here, we
report thermoelectric and electric transport experiments on two metals with
large magnetic moments on a triangular and on a slightly distorted kagom\'e
lattice, respectively. We show that the impact of chiral spin fluctuations is
strongly enhanced for the kagom\'e lattice. Both these spiral magnets have
similar magnetic phase diagrams including a periodic array of magnetic
skyrmions. However, our modelling shows that the geometry of the kagom\'e
lattice, with corner-sharing spin-trimers, helps to avoid cancellation of
Berry-phase contributions; spin fluctuations are endowed with a net chiral
habit already in the thermally disordered (paramagnetic) state. Hence, our
observations for the kagom\,e material contrast with theoretical models
treating magnetization as a continuous field, and emphasize the role of lattice
geometry on emergent electrodynamic phenomena.Comment: 16 pages, 4 figure
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