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1
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Magnetic Properties of MeB_{50} (Me = 3d Atom) Compounds

100%
Panfilov A., Grechnev G., Filipov V., Lyashchenko A., Levchenko G.
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vol. 126
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issue 1
400-401
EN
Temperature dependence of the static magnetic susceptibility for higher borides MeB_{50}, where Me = V, Cr, Mn, Fe, Co and Ni, was measured by Faraday method in the temperature range of 78-300 K. The value of effective magnetic moment of 3d-ions, resulted from the experiment, is compared with corresponding data of the ab initio calculations of the electronic structure and magnetic properties of these compounds based on the density functional theory.
2
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Investigation of Mixed Valence State of Sm_{1-x}B_{6} and Sm_{1-x}La_{x}B_{6} by XANES

86%
Gabáni S., Flachbart K., Bednarčík J., Welter E., Filipov V., Shitsevalova N.
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vol. 126
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issue 1
338-339
EN
We investigated the valence states of samarium ions in Sm deficient Sm_{1-x}B_{6} (x=0.03, 0.05, 0.08, 0.1 and 0.2) sintered samples, in single crystalline solid solutions Sm_{1-x}La_{x}B_{6} (x=0.16, 0.28, 0.4, 0.55 and 0.7) as well as in a SmB_{6} single crystal by X-ray absorption near edge structure (XANES) between 4.2 and 300 K. It was shown that the mixed valence state v_{Sm} of Sm-ions (v_{Sm} ≈ 2.51 for SmB_{6} at 4.2 K) in deficient samples is changed but maintained up to a concentration of 20% of vacancies and up to a concentration of 70% in samples doped with trivalent La-ions, and that in both cases it increases with temperature. On the other hand, the value of v_{Sm} increases with increasing vacancy level, whereas it decreases with increasing La^{3+} substitution. The obtained dependences of Sm-valence in SmB_{6} on vacancy as well as on La^{3+} ion concentration are in good agreement with susceptibility measurements and exact numerical calculation of the spinless Falicov-Kimball model in two dimensions.
3
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Magnetic Phase Diagram of TmB_{4} under High Pressure

86%
Gabáni S., Pristáš G., Takáčová I., Flachbart K., Filipov V., Shitsevalova N., Siemensmeyer K.
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vol. 126
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issue 1
356-357
EN
TmB_{4} is a Shastry-Sutherland frustrated system which exhibits very complex magnetic properties. In this contribution the phase diagram of magnetic field vs. temperature of TmB_{4} under hydrostatic pressure up to 26.5 kbar is investigated using sensitive ac-resistance measurements. Temperature and magnetic field dependences of resistance at various pressures were carried out in a piston cylinder pressure cell between 1.7 and 14 K and in magnetic fields up to 6 T. The obtained results exhibit shifts of ordering temperatures T_{N} as well as shifts of boundaries between different magnetic phases. The observed pressure dependences of T_{N} can be described by the relation d lnT_{N}/dp=+(0.16÷0.18) %/kbar. The effect of pressure on various interactions between magnetic ions in this compound is discussed.
4
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Phonon Drag and Magnetic Anomalies of Thermopower in RB_{12} (R = Ho, Er, Tm, Lu)

73%
Glushkov V., Demishev S., Ignatov M., Khayrullin E., Sluchanko N., Shitsevalov N., Levchenko A., Filipov V., Flachbart K., Siemensmeyer K.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
275-278
EN
High precision measurements of the Seebeck coefficient S(T) were carried out on the single crystals of RB_{12} (R = Ho, Er, Tm, Lu) at temperatures 2-300 K. It was shown that the effects of phonon drag result from vibrations of rare earth ions (ħω_E≈10-33 meV) in the rigid framework structure of the B_{12} clusters and determine the main contribution to thermopower at intermediate temperatures (30-300 K). The correlated behavior of transport parameters favors the appreciable enhancement of spin fluctuations in the sequence of magnetic compounds (HoB_{12}-TmB_{12}) when approaching to the valence instability state in YbB_{12}. The giant increase in S(T) detected in the vicinity of the Néel temperature T_N for HoB_{12}, ErB_{12}, and TmB_{12} seems to result from the density of states renormalization caused by antiferromagnetic ordering.
5
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Influence of Pressure on the Electrical Transport Properties of Carbon-Doped EuB₆

73%
Pristáš G., Gabáni S., Baťko I., Baťková M., Orendáč M., Gažo E., Filipov V., Konovalova E., Diko P., Flachbart K.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
982-984
EN
We have studied the influence of hydrostatic pressure on the electrical resistivity of carbon-doped semimetal EuB₆ which orders ferromagnetically at T_{C}=3.9 K and is intrinsically inhomogeneous due to fluctuations of carbon content. We observed a shift of the low-temperature resistivity maximum from 4.6 K (at 1 bar) to 5.2 K (at 30.3 kbar) with increasing pressure. However, the maximum of the derivative dρ/dT(T), which reveals the temperature of ferromagnetic ordering, does not change its position with increasing pressure. This behaviour is different from stoichiometric EuB₆, where pressure increases the ferromagnetic ordering temperature. The origin of this discrepancy may lie in the increase of volume fraction of the non-ferromagnetic phase with increase of pressure. Additional magnetoresistance measurements at various pressures between 1.5 K and 30 K have shown that with increase of magnetic field the resistivity is monotonically decreasing, and above 1 T a transition to a monotonic resistivity behaviour (dρ/dT(T)>0) is observed. Our results support the picture that carbon-rich regions play a role of "spacers", which prevent the percolation of the ferromagnetic phase.
6
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Anomalous Transport Properties of Carbon-Doped EuB_6

73%
Batkova M., Batko I., Filipov V., Flachbart K., Sechovský V., Shitsevalova N., Šantavá E., Šebek J.
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issue 5
893-894
EN
In the presented work we report electrical, magnetic and thermal properties of EuB_{6-x}C_{x} single crystals with an estimated value of x ≈ 0.07. Our studies reveal an antiferromagnetic phase transition at T_{N} ≈ 6.7 K. Electrical resistivity at zero magnetic field shows a pronounced resistivity maximum at T_{M} ≈ 7 K, just above the antiferromagnetic phase transition temperature. With increasing applied magnetic field the maximum moves to lower temperature and becomes totally suppressed at the field of 9 T. Observed magnetoresistance is negative in the whole studied temperature range 2-20 K, yielding a ratio of ρ(0 T, 7 K)/ρ(9 T, 7 K) ≈ 2.5. The origin of such magnetoresistance is associated with formation of mixed magnetic structure in the system due to fluctuation of carbon concentration.
7
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Angular Dependences of ESR Parameters in Antiferroquadrupolar Phase of CeB₆

73%
Semeno A., Gilmanov M., Sluchanko N., Krasnorussky V., Shitsevalova N., Filipov V., Flachbart K., Demishev S.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1060-1062
EN
Angular dependences of ESR line parameters (g-factor and linewidth Δ H) were experimentally explored in the antiferroquadrupolar phase of heavy fermion system CeB₆ at T=1.8 K. The data were obtained in two experimental geometries with different mutual directions of the wavevector k and the external magnetic field H at frequency of f=60 GHz. A g-factor anisotropy was found: while g-factors for [110] and [111] directions are close to each other (g ≈1.6), it is considerably higher (g ≈1.75) for [100]. The obtained angular dependence g(Θ) was compared with the theoretically predicted g-factor behavior for the Γp₈ state of Ce³⁺ ion in antiferroquadrupolar phase of CeB₆. It turns out that the experimental g-factor is considerably smaller at all angles than the theoretically calculated limits (2
8
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Bulk and Local Magnetic Susceptibility of ErB_{12}

59%
Bogach A., Bogomolov L., Glushkov V., Demishev S., Sluchanko D., Sluchanko N., Shitsevalova N., Levchenko A., Filipov V., Flachbart K., Siemensmeyer K.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
271-274
EN
High precision measurements of magnetoresistance Δρ/ρ = f(T,H) and magnetization M(T,H) were carried out on single crystals of rare-earth dodecaboride ErB_{12} at temperatures in the interval 1.8-30 K in magnetic fields up to 70 kOe. The high accuracy of the experiments allowed us to perform numerical differentiation and analyze quantitatively the behavior of the derivative d(Δρ/ρ)/dH = f(T,H) and of the magnetic susceptibility χ(T,H) = dM/dH in paramagnetic and magnetically ordered (antiferromagnetic, T_N ≈ 6.7 K and T_M ≈ 5.85 K) phases of ErB_{12}. It was shown that negative magnetoresistance anomalies observed in present study in paramagnetic state of ErB_{12} may be consistently interpreted in the framework of a simple relation between resistivity and magnetization -Δρ/ρ ~ M^2.
9
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Charge Transport and Magnetism in Tm_{0.03}Yb_{0.97}B₁₂

59%
Glushkov V., Azarevich A., Anisimov M., Bogach A., Demishev S., Dukhnenko A., Filipov V., Flachbart K., Gabáni S., Gavrilkin S., Kondrin M., Shitsevalova N., Sluchanko N.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
985-987
EN
Transport and magnetic properties of polycrystalline Tm_{0.03}Yb_{0.97}B₁₂ samples were investigated at temperatures 1.8-300 K in magnetic fields up to 9 T. The activated behavior of resistivity, the Hall coefficient and thermopower is described in terms of a narrow gap ε_g ≈ 16.6 meV, which controls the charge transport in Tm_{0.03}Yb_{0.97}B₁₂ at T>40 K. The maximum of magnetic susceptibility found at 50 K is shown to be induced by a spin gap Δ ≈ 4.7 meV being close to the half of the spin fluctuation energy in YbB₁₂. Large diffusive thermopower S=AT, A=-29.1 μV/K² and the Pauli susceptibility χ₀ ≈ 7.2×10¯³ emu/mol found below 20 K seem to be associated with the many-body resonance, which corresponds to states with an enhanced effective mass m* ≈ 250m₀ (m₀ - free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions.
10
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Magnetoresistance Anisotropy and Magnetic H-T Phase Diagram of Tm_{0.996}Yb_{0.004}B_{12}

59%
Sluchanko N., Azarevich A., Bogach A., Glushkov V., Demishev S., Gavrilkin S., Gabani S., Flachbart K., Shitsevalova N., Filipov V., Vanacken J., Moshchalkov V., Stankiewicz J.
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vol. 126
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issue 1
332-333
EN
The antiferromagnetic ground state has been studied by transverse magnetoresistance, heat capacity and magnetization measurements, which were carried out on high quality single crystals of Tm_{0.996}Yb_{0.004}B_{12} dodecaboride in strong magnetic fields at liquid helium temperatures. Both antiferromagnetic-paramagnetic (AF-P) and spin-orientation (AF1-AF2) phase transitions have been observed, and allowed to construct a complicated magnetic H-T phase diagram for this compound. Strong magnetoresistance anisotropy was found both in AF states (ρ(H||[110])/ρ(H||[111])~ 1.2 at H~ 20 kOe) and at the critical field of AF-P transition (H_{N}[100]/H_{N}[111]~ 1.25) in this magnetic metal with a simple fcc crystal structure.
11
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Anisotropy of Magnetoresistance in HoB₁₂

59%
Khoroshilov A., Krasnorussky V., Bogach A., Glushkov V., Demishev S., Levchenko A., Shitsevalova N., Filipov V., Gabáni S., Flachbart K., Anisimov M., Siemensmeyer K., Sluchanko N.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
976-978
EN
We present results of precision measurements of magnetoresistance of isotopically pure Ho¹¹B₁₂ at low temperatures 2÷10 K in magnetic field up to 80 kOe of different orientation to the crystal axes. The data obtained revealed strong anisotropy of magnetoresistance and allowed us to reconstruct magnetic H-T phase diagrams for main crystallographic directions H || [001], [110], and [111]. Analysis of magnetoresistance derivatives allowed to conclude in favor of two main magnetoresistance contributions. Among of them the negative quadratic component is attributed to charge carriers scattering on a magnetic clusters of Ho³⁺ ions (4f component) and positive linear one may be explained in terms of scattering on a spin density waves (5d component).
12
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Charge Transport and Magnetism in Eu_{1-x}Ca_{x}B_6

59%
Glushkov V., Anisimov M., Batko I., Batkova M., Bogach A., Demishev S., Filipov V., Flachbart K., Kuznetsov A., Sannikov I., Shitsevalova N., Sluchanko N.
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issue 5
891-892
EN
Transport, magnetic and thermal properties of substitutional solid solution Eu_{1 - x}Ca_{x}B_6 single crystals (0 ≤ x ≤ 0.244) have been studied at 1.8 ≤ T ≤ 300 K and in magnetic fields up to 8 T. Calcium doping is shown to result in a metal-insulator transition, which occurs at x_{MIT} ≈ 0.2. In vicinity of metal-insulator transition the effect of colossal magnetoresistance is found to be very sensitive to Ca content, the amplitude varying from Δ = [ ρ (0)- ρ (8T)]/ρ(8T) ≈1.4×10^2 to Δ ≈ 7.5 × 10^3 for 0.14 ≤ x ≤ 0.16. The analysis of magnetic contribution to heat capacity shows that a large amount of magnetic entropy ( ≈ 30%) releases in Eu_{0.845}Ca_{0.155}B_6 when moving from the Curie temperature T_{C} ≈ 5.5 K to the characteristic one T* ≈ 30 K. This observation as well as the large amplitude of low field colossal magnetoresistance effect and the deviation of magnetic susceptibility from the Curie-Weiss law detected for x = 0.155 compound in the interval T_{C} ≤ T ≤ T* seem to be associated with magnetic phase separation induced by Ca doping.
13
Content available remote

Anisotropy of the Charge Transport in GdB₆

59%
Anisimov M., Glushkov V., Bogach A., Demishev S., Samarin N., Samarin A., Shitsevalova N., Levchenko A., Filipov V., Gábani S., Flachbart K., Sluchanko N.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
973-975
EN
The anisotropy of charge transport was investigated in the antiferromagnetic II state of GdB₆ from precise measurements of transverse magnetoresistance. Based on the data obtained we detected a complicated behavior of magnetoresistance curves which are characterized by the appearance of considerable hysteresis on the field and angular dependences below T_{N2}. Moreover it was shown that the system GdB₆ is sensitive to cooling-warming prehistory. The data analysis allowed to reconstruct magnetic H-T phase diagram of GdB₆ along main crystallographic directions (H||⟨001⟩,⟨110⟩,⟨111⟩) and to propose additional phase transition inside AF II phase at H₁ ≈ 0.5 T.
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