16 research outputs found
Magnetization Plateau Observed by Ultra-High Field Faraday Rotation in a Kagom\'e Antiferromagnet Herbertsmithite
To capture the high-field magnetization process of herbertsmithite
(ZnCu3(OH)6Cl2), Faraday rotation (FR) measurements were carried out on a
single crystal in magnetic fields of up to 190 T. The magnetization data
evaluated from the FR angle exhibited a saturation behavior above 150 T at low
temperatures, which was attributed to the 1/3 magnetization plateau. The
overall behavior of the magnetization process was reproduced by theoretical
models based on the nearest-neighbor Heisenberg model. This suggests that
herbertsmithite is a proximate kagome antiferromagnet hosting an ideal quantum
spin liquid in the ground state. A distinguishing feature is the superlinear
magnetization increase, which is in contrast to the Brillouin function-type
increase observed by conventional magnetization measurements and indicates a
reduced contribution from free spins located at the Zn sites to the FR signal.Comment: 4 pages and 4 figures plus Supplemental Materia
Phase diagram of multiferroic KCuAsO(OD)
The layered compound KCuAsO(OD), comprising distorted kagome
planes of Cu ions, is a recent addition to the family of type-II
multiferroics. Previous zero field neutron diffraction work has found two
helically ordered regimes in \kns, each showing a distinct coupling between the
magnetic and ferroelectric order parameters. Here, we extend this work to
magnetic fields up to ~T using neutron powder diffraction, capacitance,
polarization, and high-field magnetization measurements, hence determining the
phase diagram. We find metamagnetic transitions in both low temperatures
phases around ~T, which neutron powder diffraction reveals
to correspond to a rotation of the helix plane away from the easy plane, as
well as a small change in the propagation vector. Furthermore, we show that the
sign of the ferroelectric polarization is reversible in a magnetic field,
although no change is observed (or expected on the basis of the magnetic
structure) due to the transition at ~T. We finally justify the temperature
dependence of the polarization in both zero-field ordered phases by a symmetry
analysis of the free energy expansion
Negative-chirality order in kagome antiferromagnet CdCu(OH)(NO)HO
The neutron diffraction and nuclear magnetic resonance (NMR) measurements
have been used to microscopically analyze the magnetic structure in the kagome antiferromagnet CdCu(OH)(NO)HO.
Below the magnetic ordering temperature K, magnetic Bragg
reflections at (110) and (100) were found in the neutron diffraction pattern,
which suggests a magnetic structure. Furthermore, the vector spin
chirality for the structure was successfully identified from the internal
field direction obtained by the N-NMR measurement. Our findings point to
a chirality-ordered magnetic structure with negative vector chirality and
anisotropy.Comment: 6 pages, 5 figure
Thermal Hall Effects of Spins and Phonons in Kagome Antiferromagnet Cd-Kapellasite
We have investigated the thermal-transport properties of the kagome
antiferromagnet Cd-kapellasite (Cd-K). We find that a field suppression effect
on the longitudinal thermal conductivity k_xx sets in below ~25 K, suggesting a
large spin contribution k_xx^sp in k_xx. We also find clear thermal Hall
signals in the spin liquid phase in all Cd-K samples. The magnitude of the
thermal Hall conductivity k_xy shows a significant dependence on the sample's
scattering time. On the other hand, the temperature dependence of k_xy is
similar in all Cd-K samples; k_xy shows a peak at almost the same temperature
of the peak of the phonon thermal conductivity k_xy^ph which is estimated by
k_xx at 15 T. These results indicate the presence of a dominant phonon thermal
Hall k_xy^ph at 15 T. In addition to k_xy^ph, we find that the field dependence
of k_xy at low fields turns out to be non-linear at low temperatures,
concomitantly with the appearance of the field suppression of k_xx, indicating
the presence of a spin thermal Hall k_xy^sp at low fields. Remarkably, by
assembling the k_xx dependene of k_xy^sp data of other kagome antiferromagnets,
we find that, whereas k_xy^sp stays a constant in the low-k_xx region, k_xy^sp
starts to increase as k_xx does in the high-k_xx region. This k_xx dependence
of k_xy^sp indicates the presence of both intrinsic and extrinsic mechanisms in
the spin thermal Hall effect in kagome antiferromagnets. Furthermore, both
k_xy^ph and k_xy^sp disappear in the antiferromagnetic ordered phase at low
fields, showing that phonons alone do not exhibit the thermal Hall effect. A
high field above ~7 T induces k_xy^ph, concomitantly with a field-induced
increase of k_xx and the specific heat, suggesting a coupling of the phonons to
the field-induced spin excitations as the origin of k_xy^ph.Comment: 33 pages, 16 figures; analyses and figures for the heat capacity and
the spin thermal Hall effect were adde
Dimensional reduction by geometrical frustration in a cubic antiferromagnet composed of tetrahedral clusters
Dimensionality is a critical factor in determining the properties of solids and is an apparent built-in character of the crystal structure. However, it can be an emergent and tunable property in geometrically frustrated spin systems. Here, we study the spin dynamics of the tetrahedral cluster antiferromagnet, pharmacosiderite, via muon spin resonance and neutron scattering. We find that the spin correlation exhibits a two-dimensional characteristic despite the isotropic connectivity of tetrahedral clusters made of spin 5/2 Fe3+ ions in the three-dimensional cubic crystal, which we ascribe to two-dimensionalisation by geometrical frustration based on spin wave calculations. Moreover, we suggest that even one-dimensionalisation occurs in the decoupled layers, generating low-energy and one-dimensional excitation modes, causing large spin fluctuation in the classical spin system. Pharmacosiderite facilitates studying the emergence of low-dimensionality and manipulating anisotropic responses arising from the dimensionality using an external magnetic field