Search results

1

Reentrant Metal-Insulator Transition in Ca_{1-x}Eu_{x}B_{6}

100%

Glushkov V., Anisimov M., Baybakov R., Demishev S., Filippov V., Flachbart K., Kuznetsov A., Shitsevalova N., Sluchanko N.

Acta Physica Polonica A

|

2014

|

vol. 126

|

issue 1

294-295

EN

Resistivity, Hall and Seebeck effects have been studied on single crystals of Ca_{1-x}Eu_{x}B_{6} (0 ≤ x ≤ 1) at temperatures 2-300 K and in magnetic fields up to 8 T. An insulating ground state is found to be limited by narrow range of Eu doping 0.6 ≤ x ≤ 0.8. This region is characterized by an enhanced colossal magnetoresistance (CMR), which reaches values of ρ(0)/ρ(7T) > 10^{6} for x = 0.63 at T < 10 K. Decreasing of Eu content in Ca_{1-x}Eu_{x}B_{6} below x* ≈ 0.6 restores the metallic ground state with moderate resistivity (ρ ~ 1 ÷ 5 mΩ·cm) and CMR amplitude (ρ(0)/ρ(7T) < 7). The second metal-insulator transition (MIT) in Ca_{1-x}Eu_{x}B_{6} is observed beyond the whole conductivity region found earlier in the narrow range of Eu doping (0.7 ≤ x ≤ 0.8). The correlation between the enhanced CMR amplitude, the onset of positive diffusive thermopower and the elevation of anomalous Hall effect, determined for Eu content 0.6 ≤ x ≤ 0.85, favors the idea that a smooth change of band structure is the main factor governing the reentrant MIT in Ca_{1-x}Eu_{x}B_{6}.

2

Charge Transport and Magnetism in Tm_{0.03}Yb_{0.97}B₁₂

81%

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

|

2017

|

vol. 131

|

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.

3

Hall Effect in GdB_{6}

81%

Anisimov M., Bogach A., Glushkov V., Demishev S., Samarin N., Shitsevalova N., Levchenko A., Filippov V., Kuznetsov A., Flachbart K., Sluchanko N.

Acta Physica Polonica A

|

2014

|

vol. 126

|

issue 1

348-349

EN

The Hall effect of GdB_{6} has been studied on high quality single crystals in the temperature range 2-150 K and in magnetic field of 1 T. The obtained data allow to detect anomalies in the antiferromagnetic (AF) phase including (i) a drastic enhancement of negative Hall coefficient below T_{N1} ≈ 15.5 K and (ii) the appearance of an anomalous Hall effect at T_{N2} ≈ 4.7 K. Possible scenarios of the AF ground state formation are discussed.

4

Defect Mode in LaB_{6}

81%

Anisimov M., Bogach A., Glushkov V., Demishev S., Samarin N., Gavrilkin S., Mitsen K., Shitsevalova N., Levchenko A., Filippov V., Gabani S., Flachbart K., Sluchanko N.

Acta Physica Polonica A

|

2014

|

vol. 126

|

issue 1

350-351

EN

The specific heat of high quality La^{N}B_{6} (N=10, 11, natural) single crystals is investigated in a wide range of temperatures 2 - 300 K. The obtained data allow to estimate correctly (i) the electronic γ· T term of specific heat (γ ≈ 2.4 mJ/(mol·K^{2})), (ii) the contribution from quasilocal vibrating mode of La^{3+} ions (Θ_{E} ≈ 150 - 152 K), (iii) the Debye-type term from rigid boron cages (Θ_{D} ≈ 1160± 40 K). Our data also suggest an additional defect-mode component (iv) which may be attributed to a contribution of 1.5% boron vacancies in LaB_{6}. The obtained results may be interpreted in terms of formation of two level systems, which appear when La^{3+} ions are displaced from their centrosymmetric positions in the cavities of rigid boron cages, apart from randomly distributed boron vacancies in the LaB_{6} matrix.

5

Anisotropy of the Charge Transport in GdB₆

81%

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

|

2017

|

vol. 131

|

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.

6

Charge Transport and Magnetism in Eu_{1-x}Ca_{x}B_6

81%

Glushkov V., Anisimov M., Batko I., Batkova M., Bogach A., Demishev S., Filipov V., Flachbart K., Kuznetsov A., Sannikov I., Shitsevalova N., Sluchanko N.

Acta Physica Polonica A

|

2010

|

vol. 118

|

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.

7

Anisotropy of Magnetoresistance in HoB₁₂

81%

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

|

2017

|

vol. 131

|

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).

Refine search results

Reentrant Metal-Insulator Transition in Ca_{1-x}Eu_{x}B_{6}

Charge Transport and Magnetism in Tm_{0.03}Yb_{0.97}B₁₂

Hall Effect in GdB_{6}

Defect Mode in LaB_{6}

Anisotropy of the Charge Transport in GdB₆

Charge Transport and Magnetism in Eu_{1-x}Ca_{x}B_6

Anisotropy of Magnetoresistance in HoB₁₂