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We have studied the radio frequency dielectric response of a system consisting of separate polar water molecules periodically arranged in nanocages formed by the crystal lattice of the gemstone beryl. Below

This work is focused on the structural and physical properties of CePt2Al2, an intermetallic compound. At room temperature, the modulated orthorhombic structure Cmme(a00)000, with q→= (0.481, 0, 0)...

Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H2O molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective. Here, we present measurements of the temperature-dependent dielectric permittivity, pyrocurrent, electric polarization and specific heat that indicate an order-disorder ferroelectric phase transition at T0 ≈ 3 K in the water dipolar lattice. Ab initio molecular dynamics and classical Monte Carlo simulations reveal that at low temperatures the water molecules form ferroelectric domains in the ab-plane that order antiferroelectrically along the channel direction. This way we achieve the long-standing goal of arranging water molecules in polar order. This is not only of high relevance in various natural systems but might open an avenue towards future applications in biocompatible nanoelectronics., Despite the apparent simplicity of a H2O molecule, the mutual ferroelectric ordering of the molecules is unresolved. Here, the authors realize a macroscopic ferroelectric phase transition in a network of dipole-dipole coupled water molecules located in nanopores of gemstone.

Low-temperature magnetic properties of Er2Zr2O7 were studied by magnetization measurements on a newly prepared single crystal. Simultaneously, powder neutron diffraction was employed to investigate its microscopic properties down to 0.3 K. Our low-temperature data demonstrate the presence of a magnetic signal (short-range correlations) by (i) bifurcation of zero-field-cooled (ZFC) and field-cooled (FC) data, and (ii) diffuse magnetic scattering signal developing well in agreement with the temperature development of bulk properties. The presented data are discussed in the frame of a spin-glass ground state in Er2Zr2O7.

Evolution of magnetism in single crystals of the van der Waals compound $\mathrm{V}{\mathrm{I}}_{3}$ in external pressure up to 7.3 GPa studied by measuring magnetization and ac magnetic susceptibility is reported. Four magnetic phase transitions, at ${T}_{1}=54.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}, {T}_{2}=53\phantom{\rule{0.16em}{0ex}}\mathrm{K}, {T}_{\mathrm{C}}=49.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and ${T}_{\mathrm{FM}}=26\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, respectively, have been observed at ambient pressure. The first two have been attributed to the onset of ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is characterized by the magnetic ordering transition at Curie temperature ${T}_{\mathrm{C}}$ and the transition between two different ferromagnetic phases ${T}_{\mathrm{FM}}$, accompanied by a structure transition from monoclinic to triclinic symmetry upon cooling. The pressure effects on magnetic parameters were studied with three independent techniques. ${T}_{\mathrm{C}}$ was found to be almost unaffected by pressures up to 0.6 GPa whereas ${T}_{\mathrm{FM}}$ increases rapidly with increasing pressure and reaches ${T}_{\mathrm{C}}$ at a triple point at \ensuremath{\approx} 0.85 GPa. At higher pressures, only one magnetic phase transition is observed moving to higher temperatures with increasing pressure to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization is significantly reduced by applying pressure (by more than 50% at 2.5 GPa) suggesting a possible pressure-induced reduction of vanadium magnetic moment. First-principles calculations of $\mathrm{V}{\mathrm{I}}_{3}$ under pressure allow us to ascribe the evolution of ${T}_{\mathrm{C}}$ with pressure to the reduction of interplanar distance, including the observed slope change at 0.6 GPa. These calculations also describe the associated band gap closing, showing that with a modest compression the material would become metallic. Overall, the large pressure range covered corresponds to a significant change of interplanar interactions. The obtained data thus allow us to shed light on how does the transition between the three-dimensional (3D) and quasi-2D system affect magnetic interactions in the system.

In recent years, due to their outstanding dielectric and magnetic properties, hexagonal ferrites (hexaferrites) have attracted considerable interest for developing electronic components of next-generation communication systems. The complex crystal structure of hexaferrites and critical dependences of their electric and magnetic properties on external factors, like magnetic or electric fields, pressure or doping, open ample opportunities for targeted tuning of these properties when designing specific devices. To that end, we explored the electromagnetic properties of the Pb-substituted barium hexaferrite, Ba1-xPbxFe12O19, a compound featuring an extremely rich set of physical phenomena that are inherent in the dielectric and magnetic subsystems of the material and are expected to have significant effect on its electromagnetic response at radio and terahertz frequencies. We performed the first detailed measurements of the AC response of single-crystalline Ba1-xPbxFe12O19 in an extremely broad spectral range from 1 Hz to 240 THz down to temperatures as low as 5 K. We fully characterized numerous microscopic phenomena that determine the broad-band dielectric response of the compound, and we analyzed their nature. This includes temperature-activated radiofrequency relaxations that were attributed to the dynamic response of magnetic/dielectric domains. The terahertz response is dominated by a ferroelectric-like soft mode with an unusual temperature behavior that we explain by means of a microscopic model. Several narrower terahertz excitations are associated with electronic transitions between the fine-structure components of the Fe2+ground state. Narrow resonances detected in the gigahertz region are presumably of magneto-electric origin. The obtained data on diverse but controllable electromagnetic properties of Ba1-xPbxFe12O19 compounds provides the researchers with information that makes the entire class of hexaferrites materials attractive for manufacturing electronic devices for the radiofrequency and terahertz ranges, such as absorbing coatings, anti-reflective coatings, absorbers, electromagnetic shields, antennas, phase shifters, filters, resonators, modulators, etc.

EuTiO 3 is an incipient ferroelectric antiferromagnet showing an anomalously strong spin-phonon coupling. We studied EuTiO 3 ceramics by terahertz (THz) time-domain spectroscopy upon varying temperature and magnetic field. We observed a large anisotropy which is due to the shift from the microwave to the sub-THz region of a ferromagnetic resonance appearing only when the external magnetic field is applied perpendicular to the magnetic component of the THz radiation.

In the antiferromagnetic phase of $\mathrm{Eu}\mathrm{Ti}{\mathrm{O}}_{3}$ ceramics, a seemingly anisotropic magnetodielectric effect (up to 2.5%) was observed via the low-frequency dielectric permittivity measured in external magnetic field below 1.9 T. We explain the effect theoretically by taking into account the demagnetizing field which effectively reduces the internal magnetic flux density by 0.6 T when the external magnetic field is applied perpendicular to the plane of the disk-shaped sample. This finding is also confirmed experimentally by magnetization measurements. The refractive index between 0.2 and 0.5 THz exhibits a large anisotropy in an external magnetic field of up to 7 T. This anisotropy is due to a shift of the ferromagnetic resonance from the microwave to the sub-THz region with external magnetic field applied perpendicular to the magnetic component of the THz radiation. This magnon observation is performed in the strong external magnetic field (above 2 T) and in both paramagnetic and antiferromagnetic phases.

This work is focused on the structural and physical properties of CePt

The effects on the rare-earth crystal-field-splitting schemes of incorporation of large spin-orbit coupling ($5d$) ions, such as ${\text{Ir}}^{\text{4}}+$, into the rare-earth pyrochlores are largely unknown. We report on the preparation, specific heat, magnetization, and inelastic neutron-scattering study of ${\text{Er}}_{\text{2}}{\text{Ir}}_{\text{2}}{\text{O}}_{\text{7}}$ pyrochlore. An anomaly in specific heat and bifurcation of zero-field cooled and field cooled magnetization indicates an ordering of the Ir sublattice below 140 K, in good agreement with other rare-earth pyrochlore iridates. The Er sublattice ordering below 2 K can be considered short range as well, following the development of specific-heat and magnetization data down to low temperatures. The inelastic neutron scattering allowed us to unambiguously determine the crystal-field (CF) eigenenergies and parameters of ${\text{Er}}_{\text{2}}{\text{Ir}}_{\text{2}}{\text{O}}_{\text{7}}$, which are dictated dominantly by nearest-neighbor anions (the oxygen cage around the Er cation). The influence of the magnetic iridium cations on the erbium CF scheme is rather moderate despite the strong spin-orbit coupling expected in a $5d$ metal, which is evident when comparing the energy spectra of this iridate and other $3d$- or $4d$-metal containing erbium pyrochlores. The determined CF parameters were subsequently utilized for calculations of magnetization and specific-heat CF contributions, leading to an excellent agreement with experimental data.

Pressure induced superconductivity in non-centrosymmetric CeRhSi

Single crystals of solid solutions of ferromagnetic superconductors UCoGe and URhGe were investigated by magnetization and specific-heat measurements. These compounds behave as anisotropic ferromagnets with the easy-magnetization direction along the orthorhombic $c$ axis. The maximum Curie temperature ${T}_{C}=\phantom{\rule{0.16em}{0ex}}20\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ has been observed in $\mathrm{UC}{\mathrm{o}}_{1\ensuremath{-}x}\mathrm{R}{\mathrm{h}}_{x}\mathrm{Ge}$ for $x=0.4$. The main interest of the study was the intriguing behavior in magnetic fields applied along the $b$ axis. The temperature dependence of the $b$-axis magnetic susceptibility exhibits a maximum at a characteristic temperature ${T}_{\mathrm{max}}$. For low Rh concentrations $(xl0.4){T}_{\mathrm{max}}g{T}_{C}$ and the magnetic entropy ${S}_{\mathrm{mag}}$ at ${T}_{C}$ is very low, whereas ${T}_{\mathrm{max}}={T}_{C}$ and the ${S}_{\mathrm{mag}}$ at ${T}_{C}$ is much higher for $x\ensuremath{\ge}0.4$. A metamagneticlike anomaly in magnetization is observed in all compounds, at a critical field which appears on a similar energy scale with the value of the corresponding ${T}_{\mathrm{max}}$. The character of three paramagnetic regimes which can be distinguished in the T-$x$ and H-$x$ phase diagrams, normal, correlated, and field polarized, is discussed in relation to the field-induced reentrant superconductivity in the parent compounds.

We report the single crystal properties of CePd2Zn3 and CePd2Ga3 compounds. The compounds were prepared by Bridgman method in high-frequency induction furnace. Both compounds adopt the hexagonal PrNi2Al3-type structure with a = 5.3914(2) A, c = 4.3012(2) A for CePd2Zn3 and a = 5.4106(8) A, c = 4.2671(8) A for CePd2Ga3, respectively. CePd2Zn3 orders antiferromagnetically below T N = 1.9 K. Magnetoresistance measurements revealed a crossover at B c = 0.95 T. CePd2Ga3 orders ferromagnetically at T C = 6.7 K. Applied hydrostatic pressure reduces the value of the Curie-temperature (rate ∂ T C / ∂ p = 0.9 K GPa − 1 ) down to 3.9 K at 3.2 GPa. Both compounds display a strong magnetocrystalline anisotropy with easy axis of magnetization perpendicular to the c-axis in the hexagonal lattice.

Pressure induced superconductivity in non-centrosymmetric CeRhSi$_{3}$ and CeIrSi$_{3}$ compounds has attracted significant attention of the scientific community since its discovery 15 years ago. Up-to-date, all reported experimental results were obtained employing the hybrid-cylinder piston pressure cells with a maximum reachable pressure of 3 GPa. Present study focuses on the superconducting state at higher, so far unreported, pressures using the Bridgman anvil cell and a CeRhSi$_{3}$ single crystal synthesized by the Sn-true-flux method. The initial increase of superconducting critical temperature from 0.4 K at 1.1 GPa to 1.1 K at 2.4 GPa is followed by a gradual suppression of SC state upon increasing the pressure above 3.0 GPa, forming a typical dome. The pressure induced superconductivity is expected to be completely suppressed in the pressure region between 4.5 and 5.0 GPa. Temperature dependence of electrical resistivity in constant magnetic fields and high pressures, as well as the magnetoresistance measurements, reveal a large critical field, exceeding 19 T at 0.6 K and 2.4 GPa, sharply decreasing receding the superconductivity dome. The previously reported $\it{T-p}$ and $\it{H-T}$ phase diagrams are completed by our high-pressure data and discussed in the frame of previous results., Comment: 16 pages, 5 figures

We present the preparation and characterization of an $\mathrm{E}{\mathrm{r}}_{2}\mathrm{Z}{\mathrm{r}}_{2}{\mathrm{O}}_{7}$ single crystal. The material was studied by means of x-ray and neutron diffraction, magnetization, AC susceptibility, and specific heat measurements. The defect-fluorite type of cubic structure, previously reported as the crystal structure of $\mathrm{E}{\mathrm{r}}_{2}\mathrm{Z}{\mathrm{r}}_{2}{\mathrm{O}}_{7}$, is consistent with our x-ray powder diffraction data. The measurements of physical properties were performed in magnetic field applied along principal crystallographic directions. A negligible directional dependence of physical properties is observed at temperatures down to 3 K, and only minor differences can be traced at lower temperatures. A low-temperature anomaly in magnetization and specific heat data and its evolution with applied magnetic field is followed. A frequency-dependent shift of freezing temperature was observed in AC susceptibility. Several origins of the observed anomaly are discussed, leaving a spin-glass state as the most probable explanation.

We have performed broad-band spectroscopic investigations of vibrational and relaxational excitations of water molecules confined to nanocages within artificial beryl and mineral cordierite crystals. Signatures of quantum critical phenomena within the H2O molecular network are registered in beryl. In cordierite, a density functional analysis is applied to reconstruct the potential energy landscape experienced by H2O molecules, revealing a pronounced anisotropy with a potential well of about 10 meV for the molecular dipole moment aligned along the b-axis. This anisotropy leads to a strongly temperature dependent and anisotropic relaxational response of the dipoles at radiofrequencies with the activation energies corresponding to the barriers of the rotational potential. At T ≈ 3 K, we identify signatures of a transition into a glassy state composed by clusters of H2O dipoles. Rich set of anisotropic and temperature-dependent excitations are observed in the terahertz frequency range which we associate with rotational/translational vibrations.

The electrical resistance, Hall resistance, and thermoelectric power of the Ising-like antiferromagnet $\mathrm{UIrS}{\mathrm{i}}_{3}$ were measured as functions of temperature and magnetic field. We have observed that the unequivocally different characters of first-order and second-order magnetic phase transitions lead to distinctly different magnetotransport properties in the neighborhood of corresponding critical temperatures and magnetic fields, respectively. The magnetic contributions to the electrical and Hall resistivity in the antiferromagnetic state, and the polarized and normal regimes of paramagnetic state are driven by different underlying mechanisms. Results of detailed measurements of magnetotransport in the vicinity of the tricritical point reveal that the Hall-resistivity steps at phase transitions change polarity just at this point. The jumps in field dependences of specific heat, electrical resistivity, Hall resistivity, and Seebeck coefficient at the first-order metamagnetic transitions indicate a Fermi surface reconstruction, which is characteristic of a magnetic-field-induced Lifshitz transition. The presented results emphasize the usefulness of measurements of electrical- and thermal-transport properties as sensitive probes of magnetic phase transformations in antiferromagnets sometimes hardly detectable by other methods.

The EuRu2P2 single crystal was investigated by means of magnetic, transport and thermodynamic studies at ambient and hydrostatic pressures. A small magnetocrystalline anisotropy with crystallographic [100] direction as an easy magnetization direction was found by experimental measurements and confirmed by first-principles calculations. We connect a previously reported change in the compressibility observed at room temperature to a rapid change of ordering temperature under applied hydrostatic pressure.

We have investigated a single crystal of the tetragonal intermetallic compound NdPd 5 Al 2 by means of magnetization, specific heat and magnetoresistivity measurements. NdPd 5 Al 2 orders antiferromagnetically below 1.3 K and exhibits a distinct magnetocrystalline anisotropy with the c -axis as the easy axis of magnetization. Magnetic phase diagram constructed on the basis of heat capacity and magnetization measurements is characterized by two different low-temperature phases and first-order phase transition in the zero field.

A new simplified synthesis of an Er 2 Ti 2 O 7 single crystal is presented. The single crystal was prepared by a floating zone technique from the unreacted stoichiometric mixture of starting oxides Er 2 O 3 and TiO 2 . No intermediate reactions of constituent oxides were conducted in contrast to previous studies. We demonstrate a good quality of prepared single crystal by both thorough (microscopic) chemical and structural characterization of the material and measurements of previously reported low-temperature properties: An Er 2 Ti 2 O 7 single crystal was characterized by means of x-ray, electron and neutron diffraction techniques, and magnetization and specific heat measurements. The low-temperature magnetization was investigated by indirect measurement employing pre-calibrated Hall probes. The obtained low-temperature data are well comparable with previous reports and document a high quality of the prepared single crystal. Presented single crystal synthesis from an unreacted precursor is prospectively applicable to other rare-earth RE 2 Ti 2 O 7 pyrochlores.

There is an ongoing dispute in the community about the absence of a magnetic quantum critical point (QCP) in the noncentrosymmetric heavy fermion compound CeRhSi3. In order to explore this question we prepared single crystals of CeRh(Si1-x Ge x )3 with x = 0.05 and 0.15 and determined the temperature-pressure (T-p) phase diagram by means of measurements of the electrical resistivity. The substitution of isoelectronic but large Ge enforces a lattice volume increase resulting in a weakening of the Kondo interaction. As a result, the x = 0.05 and x = 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures being T N = 4.7 K and T N1 = 19.7 K, respectively. Application of pressure suppresses T N (T N1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds above p ⩾ 2.16 GPa (x = 0.05) and p ⩾ 2.93 GPa (x = 0.15). Extrapolation of T N(p) → 0 of CeRh(Si0.95Ge0.05)3 yields a critical pressure of p c ≈ 3.4 GPa (in CeRh(Si0.85Ge0.15)3 p c ≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state.

Thermal expansion, magnetostriction, and magnetization measurements under magnetic field and hydrostatic pressure were performed on a ${\mathrm{UAu}}_{2}{\mathrm{Si}}_{2}$ single crystal. They revealed a large anisotropy of magnetoelastic properties manifested by prominent length changes, leading to a collapse of the unit-cell volume accompanied by breaking the fourfold symmetry (similar to that in ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$ in the hidden-order state) in the antiferromagnetic state as consequences of strong magnetoelastic coupling. The magnetostriction curves measured at higher temperatures confirm a bulk character of the $50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ weak ferromagnetic phase. The large positive pressure change of the ordering temperature predicted from Ehrenfest relation contradicts the more than an order of magnitude smaller pressure dependence observed by the magnetization and specific heat measured under hydrostatic pressure. A comprehensive magnetic phase diagram of ${\mathrm{UAu}}_{2}{\mathrm{Si}}_{2}$ in magnetic field applied along the $c$ axis is presented. The ground-state antiferromagnetic phase is suppressed by a field-induced metamagnetic transition that changes its character from second to first order at the tricritical point.

The metamagnetic transition between the antiferromagnetic and paramagnetic state in UIrGe has been studied at various temperatures by magnetization, heat capacity and magnetocaloric-effect measurements on a single crystal in static and pulsed magnetic fields applied along the orthorhombic b-axis. A first-order transition is observed at temperatures below 13 K and a second-order one at higher temperatures up to the N\'eel temperature (TN = 16.5 K). The first-order transition is accompanied by a dramatic increase of the Sommerfeld coefficient. Magnetization measurements extended to the paramagnetic range revealed an anomalous S-shape (inflection point at a magnetic field Hm) in magnetization isotherms at temperatures above 13 K and a temperature dependence of susceptibility with a maximum at Tmax well above TN. The lines representing the temperature-induced evolution of Hm and field-induced evolution of Tmax, respectively, are bound for the point in the magnetic phase diagram at which the order of metamagnetic transition changes. A tentative scenario explaining these anomalies by antiferromagnetic correlations or short-range order in the paramagnetic state is discussed., Comment: Accepted to PRB

In this paper, we report the results of an ambient and high pressure study of a 5f-electron ferromagnet URhGa. The work is focused on measurements of magnetic and thermodynamic properties of a single crystal sample and on the construction of the p-T phase diagram. Diamond anvil cells were employed to measure the magnetization and electrical resistivity pressures up to ∼ 9 GPa. At ambient pressure, URhGa exhibits collinear ferromagnetic ordering of uranium magnetic moments μU ∼ 1.1 μB (at 2 K) aligned along the c-axis of the hexagonal crystal structure below the Curie temperature TC = 41K. With the application of pressure up to 5GPa the ordering temperature TC initially increases whereas the saturated moment slightly decreases. The rather unexpected evolution is put in the context of the UTX family of compounds.

Quantum phase transitions: Tuned in metallic ferromagnets Clean ferromagnetic systems are predicted to exhibit quantum phase transitions (QPTs) rather than critical points. QPTs happen at zero temperature due to quantum fluctuations between the phases, and can be triggered by non-thermal perturbations such as hydrostatic pressure, chemical composition or magnetic fields. Jan Prokleška at Czesh Charles University and colleagues from Czech Republic and Germany demonstrate that it is possible to tune the QPT of the metallic ferromagnet UCo1-xRuxAl by pressure or weak Ru doping. The experimental study of QPTs in metallic ferromagnets is typically hindered by the extreme conditions required to drive the system into the transition, or by the presence of additional phases such as superconductivity. Instead, UCo1-xRuxAl allows to get access to the QPT at easily accessible experimental conditions, opening the possibility of studying in detail quantum critical phenomena.

In this paper, we report the results of a high pressure study of the itinerant 5f-electron ferromagnet UCoGa. The work is focused on probing the expected ferromagnet-to-paramagnet quantum phase transition induced by high pressure and on the general features of the P-T(-H) phase diagram. Diamond anvil cells were employed to measure the magnetization and electrical resistivity under pressures up to ~ 10 GPa.At ambient pressure, UCoGa exhibits collinear ferromagnetic ordering of uranium magnetic moments {\mu}U ~ 0.74 {\mu}B (at 2 K) aligned along the c-axis of the hexagonal crystal structure below Curie temperature TC = 48K. With the application of pressure, gradual decrease of both, TC and the saturated magnetic moment, has been observed up to pressures ~ 6 GPa. This is followed by a sharp drop of magnetic moment and a sudden disappearance of the magnetic order at the pressure of 6.5 GPa, suggesting a first-order phase transition, as expected for a clean system. The low temperature power law dependence of the electrical resistivity shows distinct anomalies around the ~ 6 GPa, consistent with the pressure evolution of the magnetic moment and the ordering temperature. The tricritical point of the UCoGa phase diagram is located at approximately ~ 30 K and ~ 6 GPa.