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1

Anomalies of Heat Capacity and Phase Transitions in Tm_{1-x}Yb_{x}B_{12}

100%

Sluchanko N., Azarevich A., Bogach A., Glushkov V., Demishev S., Gavrilkin S., Shitsevalova N., Fillipov V., Gabani S., Flachbart K.

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issue 5

929-930

EN

In the system Tm_{1 - x}Yb_{x}B_{12} the specific heat has been studied in a wide range of Yb-concentration in the vicinity of the quantum critical point x_{C} ≈ 0.3. The results were obtained on high quality single crystalline samples of Tm_{0.7}Yb_{0.3}B_{12} compound placed near quantum critical point, both for antiferromagnetic metals (x < x_{C}) as well as for paramagnetic insulators (x > x_{C}) within a wide temperature range of 1.9-300 K in magnetic field up to 9 T. The temperature dependence of the magnetic contribution to specific heat for Tm_{0.74}Yb_{0.26}B_{12} shows a logarithmic divergence of the form C_{mag}/T∿-lnT at T<4 K, which may be attributed to the quantum critical regime, and it is suppressed by strong external magnetic field. The Schottky anomaly of the magnetic contribution to specific heat in Tm_{1 - x}Yb_{x}B_{12} has been established and analyzed in detail.

2

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.

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vol. 126

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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.

3

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

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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.

4

Magnetoresistance Anisotropy and Magnetic H-T Phase Diagram of Tm_{0.996}Yb_{0.004}B_{12}

81%

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.

5

Superconductivity in Lu_xZr_{1-x}B_{12} Dodecaborides with Cage-Glass Crystal Structure

81%

Sluchanko N., Azarevich A., Bogach A., Gavrilkin S., Glushkov V., Demishev S., Mitsen K., Shitsevalova N., Filippov V., Gabani S., Flachbart K.

Acta Physica Polonica A

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2017

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vol. 131

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issue 4

1036-1038

EN

We probed the evolution of the superconducting transition temperature T_c and the normal state parameters of Lu_xZr_{1-x}B_{12} solid solutions employing resistivity, heat capacity and magnetization measurements. In these studies of high-quality single crystals it was found that there are two types of samples with different magnetic characteristics. An unusually strong suppression of superconductivity in Lu_xZr_{1-x}B_{12} with a rate dT_c/dx=0.21 K/at.% of Lu was observed previously on the first "magnetic" set of crystals, and it was argued to be caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium ions. On the contrary, the second (current) set of "nonmagnetic" crystals demonstrates a conventional T_c(x) dependence with a rate dT_c/dx=0.12 K/at.% of Lu which is typical for BCS-type superconductors doped by nonmagnetic impurities. The reason for this difference is yet unclear. Moreover, the H-T phase diagram of the superconducting state of Lu_xZr_{1-x}B_{12} (0 ≤ x ≤ 1) solid solutions has been deduced from magnetization measurements.

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5 Acta Physica Polonica A

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5 Bogach A.

5 Demishev S.

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5 Glushkov V.

5 Shitsevalova N.

5 Sluchanko N.

4 Azarevich A.

4 Gabani S.

2 Anisimov M.

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1 Dukhnenko A.

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1 Kondrin M.

1 Levchenko A.

1 Moshchalkov V.

1 Samarin N.

1 Stankiewicz J.

1 Vanacken J.

Anomalies of Heat Capacity and Phase Transitions in Tm_{1-x}Yb_{x}B_{12}

Defect Mode in LaB_{6}

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

Magnetoresistance Anisotropy and Magnetic H-T Phase Diagram of Tm_{0.996}Yb_{0.004}B_{12}

Superconductivity in Lu_xZr_{1-x}B_{12} Dodecaborides with Cage-Glass Crystal Structure