arXiv subjects

Jan Prokleska

Publications and source records attributed to Jan Prokleska.

12 recordsLinked to original sources

arXiv2022

Alloying driven transition between ferro- and antiferromagnetism in UTGe compounds: the UCo1-xIrxGe case

The evolution of magnetic properties of isostructural and isoelectronic solid solutions of the superconducting itinerant 5f-electron ferromagnet UCoGe with antiferromagnet UIrGe was studied by magnetization, AC susceptibility, specific heat, and electrical resistivity measurements of a series of UCo1-xIrxGe compounds in polycrystalline and single crystalline form at various temperatures and magnetic fields. Both the weak ferromagnetism and superconductivity in UCoGe were found to have vanished already for very low Ir substitution for Co x = 0.02. The antiferromagnetism of UIrGe is gradually suppressed. This is documented by a rapid decrease in both Neel temperature and the critical field of the metamagnetic transition with decreasing Ir concentration, which both tend to vanish just above x = 0.8. The section of the T-x phase diagram in the range x between 0.02 and 0.8 is dominated by a correlated paramagnetic phase exhibiting very broad bumps in temperature dependencies of b-axis magnetization and specific heat developing with increasing x. For x = 0.24, wide peaks appear in the c-axis thermomagnetic curves due to antiferromagnetic correlations which may eventually lead to frozen incoherent spin configurations at low temperatures. The correlated paramagnetic phase is also accompanied by specific electrical resistivity anomalies. The T-x phase diagram determined for the UCo1-xIrxGe compounds contrasts with the behavior of the related URh1-xIrxGe system, which was reported to exhibit an extended concentration range of stable ferromagnetism in Rh rich compounds and a discontinuous transformation between the ferromagnetic and antiferromagnetic phases at a critical Rh-Ir concentration.

cond-mat.str-el↗

arXiv2018

Magnetic field induced phenomena in UIrGe in fields applied along b axis

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 Néel 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.

cond-mat.str-el↗

arXiv2017

Unusual ferroelectric and magnetic phases in multiferroic 2H-BaMnO$_3$ ceramics

The structural phase transition in hexagonal BaMnO$_3$ occurring at $T_c$=130 K was studied in ceramic samples using electron and X-ray diffraction, second harmonic generation as well as by dielectric and lattice dynamic spectroscopies. The low-temperature phase (space group $P6_{3}cm$) is ferroelectric with a triplicated unit cell. The phase transition is driven by an optical soft mode from the Brillouin-zone boundary [$q = (\frac{1}{3},\frac{1}{3},0)$]; this mode activates in infrared and Raman spectra below $T_c$ and it hardens according to the Cochran law. Upon cooling below $T_c$, the permittivity exhibits an unusual linear increase with temperature; below 60 K, in turn, a frequency-dependent decrease is observed, which can be explained by slowing-down of ferroelectric domain wall motions. Based on our data we could not distinguish whether the high-temperature phase is paraelectric or polar (space groups $P6_{3}/mmc$ or $P6_{3}mc$, respectively). Both variants of the phase transition to the ferroelectric phase are discussed based on the Landau theory. Electron paramagnetic resonance and magnetic susceptibility measurements reveal an onset of one-dimensional antiferromagnetic ordering below $\approx220\,\rm K$ which develops fully near 140 K and, below $T_{n} \approx 59\,\rm K$, it transforms into a three-dimensional antiferromagnetic order.

cond-mat.mtrl-sci↗

arXiv2016

Electromagnon in the Z-type hexaferrite $({\rm Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$

We studied experimentally the high-temperature magnetoelectric $({\rm Ba}_{x}{\rm Sr}_{1-x})_3\rm Co_2Fe_{24}O_{41}$ prepared as ceramics (x = 0, 0.2) and a single crystal (x = 0.5) using inelastic neutron scattering, THz time-domain, Raman and far-infrared spectroscopies. The spectra, measured with varying temperature and magnetic field, reveal rich information about the collective spin and lattice excitations. In the ceramics, we observed an infrared-active magnon which is absent in $E^ω\perp z$ polarized THz spectra of the crystal, and we assume that it is an electromagnon active in $E^ω \| z$ polarized spectra. On heating from 7 to 250 K, the frequency of this electromagnon drops from 36 to 25 cm$^{-1}$ and its damping gradually increases, so it becomes overdamped at room temperature. Applying external magnetic field has a similar effect on the damping and frequency of the electromagnon, and the mode is no more observable in the THz spectra above 2 T, as the transverse-conical magnetic structure transforms into a collinear one. Raman spectra reveal another spin excitation with a slightly different frequency and much higher damping. Upon applying magnetic field higher than 3 T, in the low-frequency part of the THz spectra, a narrow excitation appears whose frequency linearly increases with magnetic field. We interpret this feature as the ferromagnetic resonance.

cond-mat.mtrl-sci↗

arXiv2015

Evolution of magnetism in Pd-substituted Ce$_2$RhIn$_8$ single crystals

The evolution of magnetism and superconductivity in Ce$_2$Rh$_{1-x}$Pd$_x$In$_8$ solid solutions has been studied within the entire concentration range by means of thermodynamic and magnetic measurements at ambient pressure and at temperatures between 0.35 K and room temperature. For this purpose, single crystals with Pd concentrations x = 0, 0.10, 0.15, 0.30, 0.45, 0.55, 0.85 and 1 have been grown from In self-flux and characterized by x-ray diffraction and microprobe analysis. Starting from the antiferromagnet Ce$_2$RhIn$_8$, the Néel temperature gradually decreases with increasing Pd concentration and the antiferromagnetism has disappeared for $x \ge 0.45$. Superconductivity has been observed only for Ce$_2$PdIn$_8$.

cond-mat.str-el↗

arXiv2015

Tuning the pressure-induced superconductivity in Pd-substituted CeRhIn5

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.

cond-mat.str-el↗

arXiv2014

Possible coupling between magnons and phonons in multiferroic CaMn7O12

Spin and lattice dynamics of CaMn7O12 ceramics were investigated using infrared, THz and inelastic neutron scattering (INS) spectroscopies in the temperature range 2 to 590 K, and, at low temperatures, in applied magnetic fields of up to 12 T. On cooling, we observed phonon splitting accompanying the structural phase transition at Tc = 450K as well as the onset of the incommensurately modulated structure at 250 K. In the two antiferromagnetic phases below T_N1 = 90K and T_N2 = 48 K, several infrared-active excitations emerge in the meV range; their frequencies correspond to the maxima in the magnon density of states obtained by INS. At the magnetic phase transitions, these modes display strong anomalies and for some of them, a transfer of dielectric strength from the higher-frequency phonons is observed. We propose that these modes are electromagnons. Remarkably, at least two of these modes remain active also in the paramagnetic phase; for this reason, we call them paraelectromagnons. In accordance with this observation, quasielastic neutron scattering revealed short-range magnetic correlations persisting within temperatures up to 500K above T_N1.

cond-mat.mtrl-sci↗

arXiv2014

Single crystal study of the layered heavy fermion compounds Ce$_2$PdIn$_8$, Ce$_3$PdIn$_{11}$, Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$

We report on single crystal growth and crystallographic parameters results of Ce$_2$PdIn$_8$, Ce$_3$PdIn$_{11}$, Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$. The Pt-systems Ce$_2$PtIn$_8$ and Ce$_3$PtIn$_{11}$ are synthesized for the first time. All these compounds are member of the Ce$_n$T$_m$In$_{3n+2m}$ (n = 1, 2,..; m = 1, 2,.. and T = transition metal) to which the extensively studied heavy fermion superconductor CeCoIn$_5$ belongs. Single crystals have been grown by In self-flux method. Differential scanning calorimetry studies were used to derive optimal growth conditions. Evidently, the maximum growth conditions for these materials should not exceed 750 $^{\circ}$C. Single crystal x-ray data show that Ce$_2$TIn$_8$ compounds crystallize in the tetragonal Ho$_2$CoGa$_8$ phase (space group P4/mmm) with lattice parameters a =4.6898(3) $Å$ and c =12.1490(8) $Å$ for the Pt-based one (Pd: a = 4.6881(4) $Å$ and c = 12.2031(8) Å). The Ce$_3$TIn$_{11}$ compounds adopt the Ce$_3$PdIn$_{11}$ structure with a = 4.6874(4) $Å$ and c = 16.8422(12) $Å$ for the Pt-based one (Pd: a = 4.6896 $Å$ and c = 16.891 Å). Specific heat experiments on Ce$_3$PtIn$_{11}$ and Ce$_3$PdIn$_{11}$ have revealed that both compounds undergo two successive magnetic transitions at T$_1$ ~ 2.2 K followed by T$_N$ ~ 2.0 K and T$_1$ ~ 1.7 K and T$_N$ ~ 1.5 K, respectively. Additionally, both compounds exhibit enhanced Sommerfeld coefficients yielding γ$_{Pt}$ = 0.300 J/mol K$^2$ Ce (γ$_{Pd}$ = 0.290 J/mol K$^2$ Ce), hence qualifying them as heavy fermion materials.

cond-mat.str-el↗

arXiv2013

Electromagnon in ferrimagnetic eps-Fe2O3 nanograin ceramics

Electromagnons are known from multiferroics as spin waves excited by the electric component of electromagnetic radiation. We report the discovery of an excitation in the far-infrared spectra of eps-Fe2O3 which we attribute to an electromagnon appearing below 110 K, where the ferrimagnetic structure becomes incommensurately modulated. Inelastic neutron scattering shows that the electromagnon energy corresponds to that of a magnon from the Brillouin zone boundary. Dielectric measurements did not reveal any sign of ferroelectricity in eps-Fe2O3 down to 10 K, despite its acentric crystal structure. This shows that the activation of an electromagnon requires, in addition to the polar ferrimagnetic structure, a modulation of the magnetic structure. We demonstrate that a combination of inelastic neutron scattering with infrared and / or terahertz spectroscopies allows detecting electromagnons in ceramics, where no crystal-orientation analysis of THz and infrared spectra is possible.

cond-mat.mtrl-sci↗

arXiv2012

Magnetic and dielectric properties of multiferroic Eu0.5Ba0.25Sr0.25TiO3 ceramics

Dielectric and magnetic properties of Eu0.5Ba0.25Sr0.25TiO3 are investigated between 10 K and 300 K in the frequency range from 10 Hz to 100 THz. A peak in permittivity revealed near 130 K and observed ferroelectric hysteresis loops prove the ferroelectric order below thistemperature. The peak in permittivity is given mainly by softening of the lowest frequency polar phonon (soft mode revealed in THz and IR spectra) that demonstrates displacive character of the phase transition. Room-temperature X-ray diffraction analysis reveals cubic structure, but the IR reflectivity spectra give evidence of a lower crystal structure, presumably tetragonal I4/mcm with tilted oxygen octahedra as it has been observed in EuTiO3. The magnetic measurements show that the antiferromagnetic order occurs below 1.8 K. Eu0.5Ba0.25Sr0.25TiO3 has three times lower coercive field than Eu0.5Ba0.5TiO3, therefore we propose this system for measurements of electric dipole moment of electron.

cond-mat.mtrl-sci↗

arXiv2012

Polar phonon anomalies in single crystalline TbScO3

Polarized infrared reflectivity spectra of a (110)-oriented TbScO3 single crystal plate were measured down to 10 K. The number of observed polar phonons active along the crystallographic c axis at low temperatures is much higher than predicted by factor-group analysis for the orthorhombic Pbnm space group. Moreover, the lowest frequency phonons active in E||c as well as in E||[1-10] polarized spectra exhibit dramatic softening tending to a lattice instability at low temperatures. The dielectric permittivity at microwave frequencies does not show any ferroelectric-like anomaly, but the dielectric loss exhibits a maximum at 100 K. The origin of the discrepancy between the number of predicted and observed polar phonons as well as the tendency toward lattice instability are discussed. Magnetic measurements reveal an antiferromagnetic phase transition near 3 K.

cond-mat.mtrl-sci↗

arXiv2010

Solution growth of Ce-Pd-In single crystals: characterization of the heavy-fermion superconductor Ce2PdIn8

Solution growth of single crystals of the recently reported new compound Ce2PdIn8 was investigated. When growing from a stoichiometry in a range 2:1:20 - 2:1:35, single crystals of CeIn3 covered by a thin (~50 um) single-crystalline layer of Ce2PdIn8 were mostly obtained. Using palladium richer compositions the thickness of the Ce2PdIn8 layers were increased, which allowed mechanical extraction of single-phase slabs of the desired compound suitable for a thorough study of magnetism and superconductivity. In some solution growth products also CePd3In6 (LaNi3In6 - type of structure) and traces of phases with the stoichiometry CePd2In7, Ce1.5Pd1.5In7 (determined only by EDX) have been identified. Magnetic measurements of the Ce2PdIn8 single crystals reveal paramagnetic behaviour of the Ce3+ ions with significant magnetocrystalline anisotropy. Above 70 K the magnetic susceptibility follows the Curie-Weiss law with considerably different values of the paramagnetic Curie temperature, for the magnetic field applied along the a- (-90 K) and c-(-50 K) axis. Below the reported critical temperature for superconductivity Tc (0.69 K) the electrical resistivity drops to zero. Comparative measurements of the electrical resistivity, heat capacity and AC susceptibility of several crystals reveal that the superconducting transition is strongly sample-dependent.

cond-mat.supr-con↗