We report a high-resolution terahertz spectroscopic study of quantum spin dynamics in the antiferromagnetic Heisenberg-Ising spin-chain compound BaCo_{2}V_{2}O_{8} as a function of temperature and ...longitudinal magnetic field. Confined spinon excitations are observed in an antiferromagnetic phase below T_{N}≃5.5 K. In a field-induced gapless phase above B_{c}=3.8 T, we identify many-body string excitations as well as low-energy fractional psinon or antipsinon excitations by comparing to Bethe ansatz calculations. In the vicinity of B_{c}, the high-energy string excitations are found to have a dominant contribution to the spin dynamics as compared with the fractional excitations.
We report on magnetization, sound-velocity, and magnetocaloric-effect measurements of the Ising-like spin-1/2 antiferromagnetic chain system BaCo_{2}V_{2}O_{8} as a function of temperature down to ...1.3 K and an applied transverse magnetic field up to 60 T. While across the Néel temperature of T_{N}∼5 K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature the field-dependent measurements reveal a sharp softening of sound velocity v(B) and a clear minimum of temperature T(B) at B_{⊥}^{c,3D}=21.4 T, indicating the suppression of the antiferromagnetic order. At higher fields, the T(B) curve shows a broad minimum at B_{⊥}^{c}=40 T, accompanied by a broad minimum in the sound velocity and a saturationlike magnetization. These features signal a quantum phase transition, which is further characterized by the divergent behavior of the Grüneisen parameter Γ_{B}∝(B-B_{⊥}^{c})^{-1}. By contrast, around the critical field, the Grüneisen parameter converges as temperature decreases, pointing to a quantum critical point of the one-dimensional transverse-field Ising model.
Abstract
The quantum Hall effect (QHE) is traditionally considered to be a purely two-dimensional (2D) phenomenon. Recently, however, a three-dimensional (3D) version of the QHE was reported in the ...Dirac semimetal ZrTe
5
. 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, spectroscopic, thermoelectric and charge transport measurements on such ZrTe
5
samples. The measured properties: magnetization, ultrasound propagation, scanning tunneling spectroscopy, and Raman spectroscopy, 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 emerges from the interplay of the intrinsic properties of the ZrTe
5
electronic structure and its Dirac-type semi-metallic character.
We present acoustic signatures of the electric quadrupolar degrees of freedom in the honeycomb-layer compound UNi4B. The transverse ultrasonic mode C66 shows softening below 30 K both in the ...paramagnetic phase and antiferromagnetic phases down to ∼ 0.33 K. Furthermore, we traced magnetic field-temperature phase diagrams up to 30 T and observed a highly anisotropic elastic response within the honeycomb layer. These observations strongly suggest that Γ6 (E2g) electric quadrupolar degrees of freedom in localized 5f2 (J = 4) states are playing an important role in the magnetic toroidal dipole order and magnetic-field-induced phases of UNi4B, and evidence some of the U ions remain in the paramagnetic state even if the system undergoes magnetic toroidal ordering.
The polarization properties of narrow spectral modes appearing in a Raman fiber laser with random distributed feedback due to Rayleigh backscattering near the lasing threshold have been studied ...experimentally. It has been shown that the modes have a high degree of polarization and that the polarization states of simultaneously generated modes are weakly correlated.
Dy2Fe14Si3 (hexagonal crystal structure of the Th2Ni17 type) is a highly-anisotropic ferrimagnet with spontaneous magnetic moment Ms = 8 μB per formula unit (at 2 K), directed along the Fe ...sublattice, and Curie temperature TC = 500 K. The magnetic anisotropy is of the easy-plane type with the 100 axis as an easy magnetization direction. Large anisotropy is observed also within the basal plane. In fields applied along the 100 and 120 axes, field-induced phase transitions were observed at 33 T (of the first order) and at 41 T (of the second order), respectively (at 2 K). Relative changes of sound velocity and changes of sound attenuation at these phase transitions in a Dy2Fe14Si3 single crystal were measured in pulsed magnetic fields up to 58 T at 2 K and elevated temperatures. The performed theoretical analysis suggests that the interaction of the elastic subsystem with the magnetic one is of the exchange-striction nature.
•Compound with hexagonal structure Dy2Fe14Si3 is highly-anisotropic ferrimagnet.•Anisotropy is of easy-plane type. The 100 axis is the easy-magnetization direction.•Magnetization along the 100 and 120 axes exhibits field-induced transitions.•Both transitions are accompanied by well-pronounced magnetoacoustic effects.•These magnetoacoustic anomalies are satisfactorily described by theory.
Magnetic properties and magnetic structures of layered GdMn2Si2 compound were studied using quasi-single crystal, high magnetic fields up to 520 kOe, and neutron powder diffraction experiment ...designed for high absorbent systems. It was shown that GdMn2Si2 has strong easy plane type magnetic anisotropy at temperatures TGd < 52 K at which Gd atoms are magnetically ordered. At temperatures 52 K < T < 453 K, the compound has antiferromagnetic ordering of Mn layers and easy axis type magnetic anisotropy with the easy axis directed along the tetragonal c-axis. The exchange-induced in-plane magnetic anisotropy of layered GdMn2Si2 at low temperatures arises to prevent magnetic frustration in Gd layers. Magnetic properties of GdMn2Si2 at temperatures below 52 K can be described within a three-sublattice model based on the Yafet-Kittel approximation.
•Magnetic structures have been determinated for the GdMn2Si2 compound with layered crystal structure.•GdMn2Si2 has strong easy plane type magnetic anisotropy at temperatures at which Gd atoms are magnetically ordered.•The Mn sublattice has uniaxial anisotropy with the easy c axis.•Easy plane magnetic anisotropy of GdMn2Si2 arises to prevent magnetic frustration in Gd layers.•Magnetic properties at T < 52 K can be described within a three-sublattice model based on the Yafet-Kittel approximation.
Fundamental characteristics of rare-earth (R) – iron intermetallics R2Fe14B are highly sensitive to the atomic substitutions and interstitial absorption of light elements. We studied a combined ...influence of the substitutions in the rare-earth sublattice and hydrogen absorption on the magnetization behavior in magnetic fields up to 60 T Er2Fe14B and Tm2Fe14B ferrimagnets chosen for the study showed that the substitution of Nd for Er or Tm increases the saturation magnetization as a result of ferromagnetic ordering of Nd and Fe moments. Under sufficiently high magnetic fields the magnetic moments rotate and the field-induced ferromagnetic state may be observed. The field at which a transition occurs is related to the strength of the inter-sublattice exchange interaction. The role of hydrogen is primarily to weaken the inter-sublattice ferrimagnetic coupling so that the reorientation becomes achievable at the available magnetic field strength (in hydrides Tm2Fe14BH5.5 and (Tm0.5Nd0.5)2Fe14BH5.5). We analyze the volume dependence of the R–Fe magnetic interaction in R2Fe14B and compare it with other R–Fe compounds.
•Characteristics of rare-earth–iron alloys are sensitive to both substitutions and interstitial absorption of light elements.•We studied a combined influence of the substitutions and hydrogen absorption on the magnetization behavior of R2Fe14B alloys.•We analyzed the volume dependence of magnetic interaction in R2Fe14B and compare it with other R–Fe compounds.
The effects of substitutional and interstitial atoms on the magnetic and magnetocaloric properties are investigated for RNi (R is rare earth) compounds attractive for magnetic solid-state cooling at ...cryogenic temperatures. We focused on combining weakly and highly anisotropic rare earth compounds and obtained GdxDy1-xNi (x = 0.1 and 0.9) compounds and their GdxDy1-xNiH3 hydrides. We observed a considerable decrease in Curie temperatures (TC) in the hydrides GdxDy1-xNiH3 compared to their parent alloys. The magnetocaloric effect (MCE) values of GdxDy1-xNiHy (y = 0 and 3) in the vicinity of TC were obtained and compared with literature data for the final GdNi and DyNi compounds. The maximum specific isothermal entropy changes -ΔsT at μ0ΔH = 5 T were 14.5, 17, and 17.5 J kg−1K−1 for GdNi, Gd0.9Dy0.1Ni, and Gd0.9Dy0.1NiH3, respectively. For DyNi, Gd0.1Dy0.9Ni, and Gd0.1Dy0.9NiH3, they were -ΔsT = 18, 15.5, and 12.5 J kg−1K−1 at μ0ΔH = 5 T, respectively. -ΔsT(H) in Gd0.9Dy0.1NiH3 at T = TC linearly increased in fields up to 7 T, while Gd0.1Dy0.9NiH3 at T ≥ TC showed a plateau-like magnetocaloric effect at μ0ΔH = 5 and 7 T. The observed effects were explained based on altered exchange and magnetocrystalline interactions in the modified compounds.
•New (GdDy)NiH3 hydrides were obtained.•In Dy-rich compounds, the hydrogenation leads to a change of a crystal structure.•Hydrogenation leads to an extremely large reduction of the Curie temperature.•The (GdDy)NiH3 hydrides obey high values of the plateau-like magnetocaloric effect.
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