31 research outputs found
Elastic Response in the Dilute non-Kramers System YPrIrZn
Ultrasonic investigations of the single-site quadrupolar Kondo effect in
diluted Pr system YPrIrZn are reported. The
elastic constant is measured down to ~40 mK using
ultrasound for the dilute system YPrIrZn and the
pure compound YIrZn. We found that the elastic constant
of the Pr-dilute system exhibits a logarithmic temperature
dependence below ~0.3 K, where non-Fermi-liquid (NFL) behavior in the
specific heat and electrical resistivity is observed. This logarithmic
temperature variation manifested in the -symmetry quadrupolar
susceptibility is consistent with the theoretical prediction of the quadrupolar
Kondo effect by D. L. Cox. On the other hand, the pure compound
YIrZn without -electron contributions shows nearly no change in
its elastic constants evidencing negligible phonon contributions. In addition,
clear acoustic de Haas-van Alphen (dHvA) oscillations in the elastic constant
were detected for both compounds on applying magnetic field. This is mainly
interpreted as contribution from the Fermi surface of YIrZn.Comment: 9 pages, 4 figures, Proceedings of J-Physics 2019 International
Conferenc
Multiferroic spin-superfluid and spin-supersolid phases in MnCr2S4
Spin supersolids and spin superfluids reveal complex canted spin structures
with independent order of longitudinal and transverse spin components. This
work addresses the question whether these exotic phases can exhibit spin-driven
ferroelectricity. Here we report the results of dielectric and pyrocurrent
measurements of MnCr2S4 as function of temperature and magnetic field up to 60
T. This sulfide chromium spinel exhibits a Yafet-Kittel type canted spin
structure at low temperatures. As function of external magnetic field, the
manganese spins undergo a sequence of ordering patterns of the transverse and
longitudinal spin components, which can be mapped onto phases as predicted by
lattice-gas models including solid, liquid, super-fluid, and supersolid phases.
By detailed dielectric and pyrocurrent measurements, we document a zoo of
multiferroic phases with sizable ferroelectric polarization strongly varying
from phase to phase. Using lattice-gas terminology, the title compound reveals
multiferroic spin-superfluid and spin-supersolid phases, while the
antiferromagnetic solid is paraelectric.Comment: 14 pages including 5 figure
Cyclotron resonance of extremely conductive 2D holes in high Ge content strained heterostructures
Cyclotron resonance has been observed in steady and pulsed magnetic fields from high conductivity holes in Ge quantum wells. The resonance positions, splittings and linewidths are compared to calculations of the hole Landau levels
High-field phase diagram of a chiral-lattice antiferromagnet Sr(TiO)Cu4(PO4)4
High-field phase diagram of a chiral-lattice antiferromagnet Sr(TiO)Cu4(PO4)4
is studied by means of the ultrasound, dielectric, and magnetocaloric-effect
measurements. These experimental techniques reveal two new phase transitions at
high fields, which have not been resolved by the previous magnetization
experiments. Specifically, the c66 acoustic mode shows drastic changes with
hysteresis with applied fields along the c axis, indicating a strong
magneto-elastic coupling. Combined with the cluster mean-field theory, we
discuss the origins of these phase transitions. By considering the chiral-twist
effect of Cu4O12 cupola units, which is inherent to the chiral crystal
structure, the phase diagram is reasonably reproduced. The agreement between
the experiment and theory suggests that this material is a unique quasi
two-dimensional spin system with competing exchange interactions and chirality,
leading to the rich phase diagram.Comment: 12 pages, 11 figures, 1 tabl
Quadrupolar Susceptibility and Magnetic Phase Diagram of PrNiCd with Non-Kramers Doublet Ground State
In this study, ultrasonic measurements were performed on a single crystal of
cubic PrNiCd, down to a temperature of 0.02 K, to investigate the
crystalline electric field ground state and search for possible phase
transitions at low temperatures. The elastic constant ,
which is related to the -symmetry quadrupolar response, exhibits the
Curie-type softening at temperatures below 30 K, which indicates that the
present system has a non-Kramers doublet ground state. A
leveling-off of the elastic response appears below 0.1 K toward the
lowest temperatures, which implies the presence of level splitting owing to a
long-range order in a finite-volume fraction associated with
-symmetry multipoles. A magnetic field-temperature phase diagram of
the present compound is constructed up to 28 T for [110]. A clear
acoustic de Haas-van Alphen signal and a possible magnetic-field-induced phase
transition at 26 T are also detected by high-magnetic-field
measurements.Comment: 13 pages, 7 figure
Origin of the quasi-quantized Hall effect in ZrTe5
The quantum Hall effect (QHE) is traditionally considered a purely
two-dimensional (2D) phenomenon. Recently, a three-dimensional (3D) version of
the QHE has been reported in the Dirac semimetal ZrTe5. It was proposed to
arise from a magnetic-field-driven Fermi surface instability, transforming the
original 3D electron system into a stack of 2D sheets. Here, we report
thermodynamic, thermoelectric and charge transport measurements on ZrTe5 in the
quantum Hall regime. The measured thermodynamic properties: magnetization and
ultrasound propagation, show no signatures of a Fermi surface instability,
consistent with in-field single crystal X-ray diffraction. Instead, a direct
comparison of the experimental data with linear response calculations based on
an effective 3D Dirac Hamiltonian suggests that the quasi-quantization of the
observed Hall response is an intrinsic property of the 3D electronic structure.
Our findings render the Hall effect in ZrTe5 a truly 3D counterpart of the QHE
in 2D systems
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Antiskyrmions and their electrical footprint in crystalline mesoscale structures of Mn1.4PtSn
Skyrmionic materials hold the potential for future information technologies, such as racetrack memories. Key to that advancement are systems that exhibit high tunability and scalability, with stored information being easy to read and write by means of all-electrical techniques. Topological magnetic excitations such as skyrmions and antiskyrmions, give rise to a characteristic topological Hall effect. However, the electrical detection of antiskyrmions, in both thin films and bulk samples has been challenging to date. Here, we apply magneto-optical microscopy combined with electrical transport to explore the antiskyrmion phase as it emerges in crystalline mesoscale structures of the Heusler magnet Mn1.4PtSn. We reveal the Hall signature of antiskyrmions in line with our theoretical model, comprising anomalous and topological components. We examine its dependence on the vertical device thickness, field orientation, and temperature. Our atomistic simulations and experimental anisotropy studies demonstrate the link between antiskyrmions and a complex magnetism that consists of competing ferromagnetic, antiferromagnetic, and chiral exchange interactions, not captured by micromagnetic simulations
Improved accuracy in high-frequency AC transport measurements in pulsed high magnetic fields
We show theoretically and experimentally that accurate transport measurements are possible even within the short time provided by pulsed magnetic fields. For this purpose, a new method has been devised, which removes the noise component of a specific frequency from the signal by taking a linear combination of the results of numerical phase detection using multiple integer periods. We also established a method to unambiguously determine the phase rotation angle in AC transport measurements using a frequency range of tens of kilohertz. We revealed that the dominant noise in low-frequency transport measurements in pulsed magnetic fields is the electromagnetic induction caused by mechanical vibrations of wire loops in inhomogeneous magnetic fields. These results strongly suggest that accurate transport measurements in short-pulsed magnets are possible when mechanical vibrations are well suppressed
Magnetotransport through graphene nanoribbons at high magnetic fields
We have investigated the magnetoresistance of lithographically prepared single-layer graphene nanoribbons in pulsed, perpendicular magnetic fields up to 60 T and performed corresponding transport simulations using a tight-binding model and several types of disorder. In experiment, at high carrier densities we observe Shubnikov-de Haas oscillations and the quantum Hall effect, while at low densities the oscillations disappear and an initially negative magnetoresistance becomes strongly positive at high magnetic fields. The strong resistance increase at very high fields and low-carrier densities is tentatively ascribed to a field-induced insulating state in the bulk graphene leads. Comparing numerical results and experiment, we demonstrate that at least edge disorder and bulk short-range impurities are important in our samples
Specific heat of EuxSrl-xTe
In this paper, we report on measurements of the specific heat C of single-crystalline EuSrTe at temperatures between 60 mK and 15 K and in magnetic fields up to 6 T. Pure antiferromagnetic EuTe shows unusual critical behavior in the vicinity of the N6el temperature T_N = 9.8 K with a positive critical exponent instead of the 3d-Heisenberg exponent a = -0.12. Possible reasons for this discrepancy between theory and experiment include magnetic anisotropy effects due to magnetic dipole-dipole interactions, which may give rise to a cross-over of the critical behavior very close to T_N. This anisotropy is also seen in the specific heat below 1 K where an exponential decay of C is observed, and in the dependence of the magnetic susceptibility on the direction of the applied field. With increasing dilution of EuTe with nonmagnetic Sr, the critical behavior changes: a becomes negative and decreases continuously. This concentration dependence of a was previously observed in the diluted ferromagnetic system EuSrS. Our data thus support that the apparent change in the critical behavior depends on the degree of disorder. Samples with concentration x lower than the critical concentration x_c reveal spin-glass behavior in the specific heat. In addition, the dependence of T_N on magnetic fields is discussed