277 research outputs found
Magnon topology and thermal Hall effect in trimerized triangular lattice antiferromagnet
The non-trivial magnon band topology and its consequent responses have been
extensively studied in two-dimensional magnetisms. However, the triangular
lattice antiferromagnet (TLAF), the best-known frustrated two-dimensional
magnet, has received less attention than the closely related Kagome system,
because of the spin-chirality cancellation in the umbrella ground state of the
undistorted TLAF. In this work, we study the band topology and the thermal Hall
effect (THE) of the TLAF with (anti-)trimerization distortion under the
external perpendicular magnetic field using the linearized spin wave theory. We
show that the spin-chirality cancellation is removed in such case, giving rise
to the non-trivial magnon band topology and the finite THE. Moreover, the
magnon bands exhibit band topology transitions tuned by the magnetic field. We
demonstrate that such transitions are accompanied by the logarithmic divergence
of the first derivative of the thermal Hall conductivity. Finally, we examine
the above consequences by calculating the THE in the hexagonal manganite
YMnO, well known to have anti-trimerization.Comment: 6 + 7 pages, 3 + 5 figures, 0 + 1 table; Journal reference adde
Size Dependence of Metal-Insulator Transition in Stoichiometric Fe3O4 Nanocrystals
Magnetite (Fe3O4) is one of the most actively studied materials with a famous
metal-insulator transition (MIT), so-called the Verwey transition at around 123
K. Despite the recent progress in synthesis and characterization of Fe3O4
nanocrystals (NCs), it is still an open question how the Verwey transition
changes on a nanometer scale. We herein report the systematic studies on size
dependence of the Verwey transition of stoichiometric Fe3O4 NCs. We have
successfully synthesized stoichiometric and uniform-sized Fe3O4 NCs with sizes
ranging from 5 to 100 nm. These stoichiometric Fe3O4 NCs show the Verwey
transition when they are characterized by conductance, magnetization, cryo-XRD,
and heat capacity measurements. The Verwey transition is weakly size-dependent
and becomes suppressed in NCs smaller than 20 nm before disappearing completely
for less than 6 nm, which is a clear, yet highly interesting indication of a
size effect of this well-known phenomena. Our current work will shed new light
on this ages-old problem of Verwey transition.Comment: 18 pages, 4 figures, Nano Letters (accepted
Robustness of the intrinsic anomalous Hall effect in Fe3GeTe2 to a uniaxial strain
Fe3GeTe2 (FGT), a ferromagnetic van der Waals topological nodal line
semimetal, has recently been studied. Using first-principles calculations and
symmetry analysis, we investigate the effect of a uniaxial tensile strain on
the nodal line and the resultant intrinsic anomalous Hall effect (AHE). Our
results reveal their robustness to the in-plane strain. Moreover, the intrinsic
AHE remains robust even for artificial adjustment of the atomic positions
introduced to break the crystalline symmetries of FGT. When the spin-orbit
coupling is absent, the nodal line degeneracy remains intact as long as the
inversion symmetry or the two-fold screw symmetry is maintained, which reveal
that the nodal line may emerge much more easily than previously predicted. This
strong robustness is surprising and disagrees with the previous experimental
report [Y. Wang et al., Adv. Mater. 32, 2004533 (2020)], which reports that a
uniaxial strain of less than 1 % of the in-plane lattice constant can double
the anomalous Hall resistance. This discrepancy implies that the present
understanding of the AHE in FGT is incomplete. The possible origins of this
discrepancy are discussed.Comment: 7 pages, 3 figure
Suppression of magnetic ordering in XXZ-type antiferromagnetic monolayer NiPS3
How a certain ground state of complex physical systems emerges, especially in
two-dimensional materials, is a fundamental question in condensed-matter
physics. A particularly interesting case is systems belonging to the class of
XY Hamiltonian where the magnetic order parameter of conventional nature is
unstable in two-dimensional materials leading to a
Berezinskii-Kosterlitz-Thouless transition. Here, we report how the XXZ-type
antiferromagnetic order of a magnetic van der Waals material, NiPS3, behaves
upon reducing the thickness and ultimately becomes unstable in the monolayer
limit. Our experimental data are consistent with the findings based on
renormalization group theory that at low temperatures a two-dimensional XXZ
system behaves like a two-dimensional XY one, which cannot have a long-range
order at finite temperatures. This work provides experimental examination of
the XY magnetism in the atomically thin limit and opens new opportunities of
exploiting these fundamental theorems of magnetism using magnetic van der Waals
materials.Comment: 57 pages, 24 figures (including Supplementary Information
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