Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H
O 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 T
≈ 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.
•EuRu2P2 is a ferromagnet with a small anisotropy with a as an easy magnetization axis.•The magnetocrystalline anisotropy was confirmed by ab-initio calculations.•Full saturated magnetic moment ...confirms the Eu2 + state over all pressures.•Sudden drop of Tc at 1.5 GPa is ascribed to the lattice compressibility change.
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.
Evolution of magnetism in single crystals of the van der Waals compound VI3 in external pressure up to 7.3 GPa studied by measuring magnetization and ac magnetic susceptibility is reported. Four ...magnetic phase transitions, at T1 = 54.5 K, T2 = 53 K, TC = 49.5 K, and TFM = 26 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 TC and the transition between two different ferromagnetic phases TFM, accompanied by a structure transition from monoclinic to triclinic symmetry upon cooling. The pressure effects on magnetic parameters were studied with three independent techniques. TC was found to be almost unaffected by pressures up to 0.6 GPa whereas TFM increases rapidly with increasing pressure and reaches TC at a triple point at ≈ 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 VI3 under pressure allow us to ascribe the evolution of TC 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 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
μ
U
∼
0.74
μ
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 ∼ 30K and ∼ 6GPa.
Abstract
Due to their outstanding dielectric and magnetic properties, hexaferrites are attracting ever-increasing attention for developing electronic components of next-generation communication ...systems. The complex crystal structure of hexaferrites and the critical dependences of their electric and magnetic properties on external factors, such as magnetic/electric fields, pressure, and doping, open ample opportunities for targeted tuning of these properties when designing specific devices. Here we explored the electromagnetic properties of lead-substituted barium hexaferrite, Ba
1−
x
Pb
x
Fe
12
O
19
, a compound featuring an extremely rich set of physical phenomena that are inherent in the dielectric and magnetic subsystems and can have a significant effect on its electromagnetic response at terahertz frequencies. We performed the first detailed measurements of the temperature-dependent (5–300 K) dielectric response of single-crystalline Ba
1−
x
Pb
x
Fe
12
O
19
in an extremely broad spectral range of 1 Hz–240 THz. We fully analyzed numerous phenomena with a corresponding wide distribution of specific energies that can affect the terahertz properties of the material. The most important fundamental finding is the observation of a ferroelectric-like terahertz excitation with an unusual temperature behavior of its frequency and strength. We suggest microscopic models that explain the origin of the excitation and its nonstandard temperature evolution. Several narrower terahertz excitations are associated with electronic transitions between the fine-structure components of the Fe
2+
ground state. The discovered radio-frequency relaxations are attributed to the response of magnetic domains. Gigahertz resonances are presumably of magnetoelectric origin. The obtained data on diverse electromagnetic properties of Ba
1−
x
Pb
x
Fe
12
O
19
compounds provide information that makes the entire class of hexaferrites attractive for manufacturing electronic devices for the terahertz range.
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.
The electrical resistance, Hall resistance, and thermoelectric power of the Ising-like antiferromagnet UIrSi3 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.
UCoGa and URhGa, two isostructural compounds, show opposite signs of the initial response of Curie temperature to applied hydrostatic pressure. To determine the physical origin of this difference the ...magnetization data measured with respect to temperature, magnetic field, and hydrostatic pressure were analyzed in the framework of the Takahashi spin-fluctuation theory. The parametersT0 and TA characterizing the distribution widths of the spin-fluctuation spectrum in the energy and wave-vector space, respectively, and TC/T0, the degree of the 5f-electron localization, have been determined. Examination of available experimental data for the other UTX (T = a transition metal, X = Al, Ga) ferromagnets having the ZrNiAl-type structure revealed some correlations between the degree of the 5f-electron localization represented by the spin-fluctuation parameters and the response of Curie temperature on the applied pressure. The extent to which this correlation can be used to describe the localization and magnetic behavior of other uranium ferromagnetic compounds is discussed.
Possible biological side effects of exposure to X-rays are stochastic effects such as carcinogenesis and genetic alterations. In recent years, a number of new studies have been published about the ...special cancer risk that children may suffer from diagnostic X-rays. Children and adolescents who constitute many of the probands in forensic age-estimation proceedings are considerably more sensitive to the carcinogenic risks of ionizing radiation than adults. Established doses for X-ray examinations in forensic age estimations vary from less than 0.1 μSv (left hand X-ray) up to more than 800 μSv (computed tomography). Computed tomography in children, as a relatively high-dose procedure, is of particular interest because the doses involved are near to the lower limit of the doses observed and analyzed in A-bombing survivor studies. From these studies, direct epidemiological data exist concerning the lifetime cancer risk. Since there is no medical indication for forensic age examinations, it should be stressed that only safe methods are generally acceptable. This paper reviews current knowledge on cancer risks associated with diagnostic radiation and aims to help forensic experts, dentists, and pediatricians evaluate the risk from radiation when using X-rays in age-estimation procedures.
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