Unconventional Hall response in the quantum limit of HfTe5

Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit

Observation of a three-dimensional fractional Hall response in HfTe5

Interacting electrons in two dimensions can bind magnetic flux lines to form composite quasiparticles with fractional electric charge, manifesting themselves in the fractional quantum Hall effect (FQHE). Although the FQHE has also been predicted to occur in three dimensions, it has not yet been experimentally observed. Here, we report the observation of fractional plateaus in the Hall conductivity of the bulk semimetal HfTe5 at magnetic fields beyond the quantum limit. The plateaus are accompanied by Shubnikov-de Haas minima of the longitudinal electrical resistivity. The height of the Hall plateaus is given by twice the Fermi wave vector in the direction of the applied magnetic field and scales with integer and particular fractional multiples of the conductance quantum. Our findings are consistent with strong electron-electron interactions, stabilizing a fractionalized variant of the Hall effect in three dimensions.Comment: 35 pages with 17 figure

Magnetic order and single-ion anisotropy in Tb3_3Ga5_5O12_{12}

Terbium gallium garnet (TGG), Tb$_3$Ga$_5$O$_{12}$, is well known for its applications in laser optics but also exhibits complex low-temperature magnetism that is not yet fully understood. Its low-temperature magnetic order is determined by means of time-of-flight neutron powder diffraction. It is found to be a multiaxial antiferromagnet with magnetic Tb$^{3+}$ ions forming six sublattices of magnetic moments aligned parallel and antiparallel to the ⟨100⟩ crystallographic directions of the cubic unit cell. The structure displays strong easy-axis anisotropy with respect to a twofold axis of symmetry in the local orthorhombic environment of the Tb$^{3+}$ sites. The crystal-field splitting within the single-ion ground-state manifold is investigated by inelastic neutron scattering on powder samples. A strong temperature dependence of the quasidoublet ground state is observed and revised parameters of the crystal-field Hamiltonian are given. The results of bulk magnetic susceptibility and magnetization measurements are in good agreement with values based on the crystal-field model down to 20 K, where the onset of magnetic correlations is observed

Synthesis and potential applications of the modified ordered mesoporous silicas

For many years design and synthesis of inexpensive, environmentally friendly and selective solid catalysts, has been an important and challenging goal in chemical research. Hybrid materials are of interest from the commercial and scientific point of view because they potentially offer the combination of inorganic and organic properties. In 1999 three groups independently developed a novel class of organic-inorganic nanocomposites, known as PMO’s (Periodic Mesoporous Organosilicas). In those materials organic groups are located within the structural tectons bridging at least two Si tetrahedral centers. Functional moieties may be incorporated into silica matrix in three different ways: 1) by grafting trialcoxyorganosilanes (R’O)3SiR onto the surface of silica; 2) by applying “one-pot” synthesis, which is based on the hydrolysis and condensation between a simple alcoxysilane (R’O)4Si and trialcoxyorganosilanes bearing functional groups (R’O)3SiR; 3) by a condensation of bis-silylated organic compounds (R’O)3Si–R–(OR’)3. So far the PMO-related research was focused mainly on the incorporation of various organic groups in order to design materials for adsorption applications and only limited number of materials was designed for catalysis. However, it is supposed that modifications with heteroatoms will alter chemical and physical properties of these materials due to large difference in the valence, coordination number, atomic weight and electronegativity between silicon and metallic elements. It is already known that pure silicas or organosilicas themselves are catalytically inactive in many reactions. Nevertheless, when metal atoms such as Al, Ti or other d-elements are incorporated into their frameworks, catalytically active sites can be generated

Spectrophotometric determination of UV protection provided by cosmetic products with sunscreen properties

Ze względu na stale rosnącą świadomość negatywnego wpływu promieniowania UV na ludzką skórę, zapewnienie właściwości promieniochronnych przez odpowiednie filtry UV staje się coraz istotniejszą kwestią. Coraz więcej badań potwierdza, że nie tylko uważane do tej pory za najbardziej inwazyjne promieniowanie z zakresu UVB (290÷320 nm), ale również UVA (320÷400 nm) stanowi poważne zagrożenie dla ludzkiej skóry. Możliwość oceny właściwości promieniochronnych filtrów UV w zakresie UVB zapewnia tzw. czynnik SPF (Sun Protection Factor). Opracowanych zostało również wiele metod pozwalających na oszacowanie parametrów ochrony przed promieniowaniem z zakresu UVA. Wśród tych metod techniki spektrofotometryczne odgrywają niezwykle istotną rolę.The UV protection provided by sunscreens is an issue of raising importance due to the constantly increasing knowledge about the negative effects that UV radiation induces in the human skin. A number of recent studies have shown that not only the most damaging UVB irradiation (290÷320 nm), but also UVA irradiation (320÷400 nm) causes skin damage. The rating system for sunscreens in the UVB range may be provided by a Sun Protection Factor (SPF) value. Lately, the scientific methods for evaluation of the protection level in the UVA region have been also developed. Among them spectrophotometric techniques are the most important ones

Synthesis and characterization of metallic oxides with potential use in cosmetic products

Celem prezentowanych badań była synteza oraz charakterystyka wybranych tlenków metali (TiO2, ZnO2, ZnO, CeO2 o właściwościach promieniochronnych w zakresie UV, jak również tlenków możliwych do wykorzystania jako pigmenty w wybranych formulacjach kosmetycznych (Fe2O3 oraz układy Fe2O3/SiO2). W celu określenia potencjalnej przydatności otrzymanych tlenków jako środków promieniochronnych lub barwiących w kosmetykach, zostały zbadane ich właściwości fizykochemiczne, a w szczególności barwa, zdolności absorpcyjne w zakresie UV-Vis, parametry teksturalne i struktura krystalograficzna.The aim of the study was to synthesize and characterize some metallic oxides (TiO2, ZnO2, ZnO, CeO2) with potential UV protection properties, as well as oxides that can be used as pigments in cosmetic formulations, namely Fe2O3 and Fe2O3/SiO2 systems. Physicochemical properties of the synthesized oxides, especially coloration, absorbing power in the UV-Vis region, textural parameters and crystallographic structures were examined

β-Carotene as an exemplary carotenoid and its application in cosmetic industry

Karotenoidy stanowią grupę związków niezwykle cennych pod względem właściwości pielęgnacyjnych, gdyż pochłaniają one nadmiar promieniowania UV, wiążą wolne rodniki i nadają skórze ładny koloryt. Dodatkowo, β-karoten jest prowitaminą dla witaminy A, która warunkuje szybką regenerację naskórka i jego wzrost. Wszystkie te czynniki powodują, że karotenoidy, a w szczególności βkaroten, znajdują wiele zastosowań w produktach kosmetycznych.Carotenoids may be considered as very useful compounds for cosmetic industry due to their ability to absorb UV radiation and to neutralise free radicals. They may also give an esthetical colour to the human skin. In addition, one of the carotenoids, namely β-carotene, is a precursor of vitamin A, which is, in turn, responsible for the regeneration and growth of the epidermis. These features make all carotenoids, in particular β-carotene, highly valuable compounds for application in the cosmetic products

Noncollinear magnetic order in epitaxial thin films of the centrosymmetric MnPtGa hard magnet

Magnetic systems exhibiting spin-canted states have garnered much attention recently for their promising rich exotic properties driven by the real-space spin textures and competing magnetic orders. In this study, we present the structural and magnetic properties of hexagonal 60 nm MnPtGa epitaxial thin films grown by magnetron sputtering on Al2O3(0001) single-crystalline substrates. The MnPtGa film crystallizes in the centrosymmetric P6(3)/mmc (No. 194) space group, showing perpendicular magnetic anisotropy along the c-axis, with a Curie temperature T-C = 263 K. In addition, the MnPtGa film undergoes a spin reorientation transition at T-sr = 160 K. We investigated the MnPtGa magnetic ground states using single-crystal neutron diffraction. A structurally forbidden (001) magnetic Bragg reflection emerges below T-sr, indicating the existence of a spin-canted state, where the magnetic moments align ferromagnetically perpendicular to the basal plane, and a non-zero in-plane component exhibits an antiferromagnetic ordering along the c-axis. At 2 K, the refined magnetic moments of Mn are mu(z) = 4.2(4) mu(B) and mu(x) = 1.5(3) mu(B), projected onto the c-axis and basal plane, respectively. Hence, we determined a 20 degrees Mn spin canting angle off from the c-axis