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.
Dielectric response of perovskite Sr1−xBaxMnO3 (x = 0.43 and 0.45) ceramics was investigated using microwave, THz and infrared spectroscopic techniques in order to study the ferroelectric and ...antiferromagnetic phase transitions with critical temperatures TC 350 K and TN 200 K, respectively. The two lowest-frequency polar phonons are overdamped above TN and they exhibit pronounced softening on heating towards TC. Nevertheless, permittivity ′ in the THz range shows only a small anomaly at TC because the phonon contribution to ′ is rather small. The phonons are coupled with a central mode which provides the main contribution to the dielectric anomaly at TC. Thus, the ferroelectric phase transition has characteristics of a crossover from displacive to order-disorder type. At the same time, the intrinsic THz central peak is partially screened by conductivity and related Maxwell-Wagner relaxation, which dominates the microwave and lower-frequency spectra. Below TN, the ferroelectric distortion markedly decreases, which has an influence on the frequencies of both the central and soft modes. Therefore, ′ in the THz range increases at TN on cooling. In spite of the strong spin-phonon coupling near TN, surprisingly no magnetodielectric effect was observed in the THz spectra upon applying magnetic field of up to 7 T, which is in contradiction with the theoretically expected huge magnetoelectric coupling. We explain this fact as due to the insensitivity of TN to magnetic field.
The effect of substituting Rh in CeRh1−xPdxIn5 with Pd up to x = 0.25 has been studied on single crystals. The crystals have been grown by means of the In self-flux method and characterized by x-ray ...diffraction and microprobe. The tetragonal HoCoGa5-type of structure and the c/a ratio of the parent compound remains intact by the Pd substitution; the unit cell volume increases by 0.6% with x = 0.25 of Pd. The low-temperature behavior of resistivity was studied also under hydrostatic pressure up to 2.25 GPa. The Pd substitution for Rh affects the magnetic behavior and the maximum value of the superconducting transition temperature measured at pressures above 2 GPa only negligibly. On the other hand, the results provide evidence that superconductivity in CeRh0.75Pd0.25In5 is induced at significantly lower pressures, i.e. the Pd substitution for Rh shifts the CeRh1−xPdxIn5 system closer to coexistence of magnetism and superconductivity at ambient pressure.
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.
Infrared reflectance measurements have been carried on highly p-type Bi2Te3 crystals over the broad temperature range from 10 to 650 K and their response function investigated. An anomalous ...nonmonotonous temperature dependence of the plasma edge frequency is observed-with a pronounced redshift and blueshift that appear above and below room temperature, respectively. Such behavior is explained in terms of the temperature evolution of the free carrier optical weight N/m∗ given by particular temperature dependence of the total carrier concentration N (determined by transport measurements) and characteristic (optical) mass m∗. The effective mass strongly varies from m∗ = 0.1 m0(m0 electron rest mass) at 10 K to m∗ = 0.5 m0 respective m∗ = 0.9 m0 at 650 K depending on the evaluating procedure. The interpretation is corroborated by complementary magnetotransport and magnetoreflectivity experiments.
Abstract
The heavy fermion paramagnet UTe
2
exhibits numerous characteristics of spin-triplet superconductivity. Efforts to understand the microscopic details of this exotic superconductivity have ...been impeded by uncertainty regarding the underlying electronic structure. Here we directly probe the Fermi surface of UTe
2
by measuring magnetic quantum oscillations in pristine quality crystals. We find an angular profile of quantum oscillatory frequency and amplitude that is characteristic of a quasi-2D Fermi surface, which we find is well described by two cylindrical Fermi sheets of electron- and hole-type respectively. Additionally, we find that both cylindrical Fermi sheets possess considerable undulation but negligible small-scale corrugation, which may allow for their near-nesting and therefore promote magnetic fluctuations that enhance the triplet pairing mechanism. Importantly, we find no evidence for the presence of any 3D Fermi surface sections. Our results place strong constraints on the possible symmetry of the superconducting order parameter in UTe
2
.
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.
•Thermal expansion of Ce2Pd2In is anisotropic having opposite sign along a or c.•Ce magnetic moments and long-range order are remarkably stable in applied pressures.•Hydrostatic pressure promotes ...antiferromagnetism on the account of ferromagnetism.•Uniaxial pressure along c-axis has no significant effect on transition temperatures.•Two types of magnetic order in Ce2Pd2In are effectively degenerate.
Among a large group of R2T2X intermetallics (R = rare earth, T = transition element, X = p-metal) crystallizing in the Shastry-Sutherland-like tetragonal structure, Ce2Pd2In represents a rare example of Ce-based ferromagnet, reached, however via an antiferromagnetic phase stable at higher temperatures. Here we describe the development of magnetism in Ce2Pd2In under external hydrostatic and uniaxial pressure, monitored by means of electrical resistivity, magnetization, and AC magnetic susceptibility experiments on a high-quality single crystal. The experiments prove a stability of the 4f magnetism in pressures up to 3 GPa. At these pressures only slightly reduced spontaneous magnetization in the FM state and enhanced electrical resistivity with signs of Kondo lattice behavior are observed. The AFM Néel temperature (TN = 4.65 K) is essentially pressure independent, while the Curie temperature (TC = 4.16 K at ambient pressure) significantly decreases under hydrostatic pressure. The fact that the ferromagnetic phase can be re-entered in weak magnetic fields (0.05 T) proves that the two types of magnetic order are effectively degenerate. Interestingly, TC is not affected by uniaxial pressure applied along the tetragonal c-axis, TN value exhibits only a weak decrease of 0.25 K GPa−1 under such uniaxial pressure. The crystal structure of Ce2Pd2In exhibits a strongly anisotropic thermal expansion with anomalous expansion of the c-parameter with decreasing T. Modest size of magnetostriction effects, observed by dilatometry at ambient pressure, indicates only regular magnetovolume interactions.
Thermal expansion, magnetostriction, and magnetization measurements under magnetic field and hydrostatic pressure were performed on a UAu2Si2 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 URu2Si2 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 50K 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 UAu2Si2 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.
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