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1
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Unusual Electron Transport Properties of U_{0.05}Y_{0.95}Al_2

100%
Tran V.
Acta Physica Polonica A
|
2008
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vol. 113
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issue 1
387-390
EN
We report a detailed study of the resistivity (ρ(T)) and thermoelectric power (S(T)) of the alloy U_{0.05}Y_{0.95}Al_2, which crystallises in the cubic MgCu_2-type structure. The resistivity is found to follow ρ(T) ∝ ln T between 15 and 40 K and a quasi-linear temperature dependence -T^{1.16} for T <10 K. At a magnetic field of 9 T a Kondo-type maximum occurs in the resistivity data at 7 K, below which the Fermi liquid behaviour (ρ(T) ∝ T^2) is recovered. S(T)/T shows a T^{0.5} power law for T <12 K. The low-temperature unconventional features observed in U_{0.05}Y_{0.95}Al_2 are presumably due to the presence of the two-channel Kondo effect.
2
Content available remote

Intriguing Magnetoresistivity of URh_{0.62}Ru_{0.38}Ge in the Non-Fermi Liquid Regime

64%
Miiller W., Tran V.
Acta Physica Polonica A
|
2009
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vol. 115
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issue 1
144-146
EN
Magnetoresistivity of URh_{0.62}Ru_{0.38}Ge solid solution was measured in the temperature range 0.35-300 K and in magnetic fields up to 9 T. For the studied system, which lies on the border of ferromagnetism, we observe positive magnetoresistivity in the non-Fermi liquid regime. The finding is in striking disagreement with scenario predicted for ferromagnetic quantum critical point.
3
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Hybridization Effects in UCu_{5-x}Au_{x} Compounds

64%
Tran V., Troć R.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
287-292
EN
We review the results of bulk and neutron diffraction measurements on the UCu_{5-x}Au_{x} system crystallizing in the cubic AuBe_{5}-type structure. The observed properties may be understood in the light of competition between Kondo effect and RKKY exchange interactions. Effects of 5f-ligand hybridization between the U-atoms occupying the 4a-sites and the Au- or/and Cu-atoms placed at the 4c- and 16e-positions, respectively, are supposed to be different. We show that the prefential occupation of 4c-sites by Au has a marked effect on the magnetic properties of the investigated system.
4
Content available remote

Electronic Structure of Th₇Ru₃

64%
Sahakyan M., Tran V.
Acta Physica Polonica A
|
2018
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vol. 133
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issue 3
751-754
EN
We report the results of scalar and fully relativistic electronic structure calculations for nonsuperconducting Th₇Ru₃, using the full-potential linearized-muffin-thin-orbital and full-potential linearized augmented-plane wave methods. The obtained data, including electronic band structures, density of states, Fermi surfaces and electron localization function, reveal the presence of anisotropic spin-orbit coupling but its strength, exposed by splitting energies of the order of 10-40 meV, is much weaker as compared to those of Th₇Fe₃ or Th₇Co₃ superconductors. Moreover, the lack of Van Hove singularity near the Fermi level underscores a key point of the non-occurrence of superconductivity in the studied compound.
5
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Ru_3Sn_7: Phonon Reference for Superconducting Mo_3Sb_7

64%
Tran V., Miiller W.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
83-85
EN
In order to search for phonon reference for dimer-gapped superconducting Mo_3Sb_7, measurements of specific heat (C_p(T)) and electrical resistivity (ρ(T)) of Ru_3Sn_7 were performed in the temperature range 2-300 K. The phonon part of C_p(T) and ρ(T) of Ru_3Sn_7 can satisfactorily be explained describing the spectrum with one Einstein and two Debye modes. We found Θp_{E} ≈ 100 K, Θp_{D1} ≈ 185 K and Θp_{D2} ≈298 K. The magnetic specific heat of Mo_3Sb_7 exhibits a sharp maximum at T*= 50 K, below which follows a gap function. Magnetic resistivity increases as -lnT with decreasing temperature and shows maximum at T*.
6
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Anomalous Magnetic Properties of URuGa

64%
Tran V., Troć R.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 2
299-302
EN
We present data of the magnetic susceptibility χ(T) and electrical resistivity ρ(T) for the hexagonal URuGa (space group P6̅2m). Below 7 K, χ increases rapidly and the data can be described by the expression χ(T) = χ(0)(1-a√T). ρ(T) in zero field follows the activated form: ρ(T)∼ exp(E_{a}/2k_{B}T ) with E_{a} = 1.9 meV. In an applied magnetic field of 1 T, the resistivity varies as ρ(T)∼ bT. Between 18 and 250 K the resistivity is linear in -lnT and consistent with a Kondo-like effect.
7
Content available remote

Electronic Band Structure of Ru₃Sn₇

64%
Sahakyan M., Tran V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
303-305
EN
The first-principle band structure calculations for Ru₃Sn₇ and Mo₃Sb₇ were carried out using the full-potential linearized muffin tin orbital method. It was shown that the valence band contribution is mainly due to the 4d electrons of Ru(Mo), while the contribution from the 5p-Sn(Sb) orbitals is relatively small. Furthermore, the 4d and 5p orbitals located near the Fermi level have the non-hybridized characters, thus presumably contributing independently to the total density of states. A comparison of the density of states of two compounds reveals an essential difference in the structures and magnitudes. We estimated the mass enhancement factor and Stoner product and discussed these differences regarding to electronic and magnetic behaviour of these compounds.
8
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Non-Fermi-Liquid State in URu_{0.68}Pd_{0.32}Ge

64%
Tran V., Gralak D.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
312-314
EN
We report the measurements of dc-magnetization (M), specific heat (C_{p}) and electrical resistivity (ρ) of an intermetallic URu_{0.68}Pd_{0.32}Ge, that lies at the border between nonmagnetic and magnetic regimes in the magnetic phase diagram of solid solutions URu_{1-x}Pd_{x}Ge. The studied composition shows enhanced dc-magnetic susceptibility χ(T) and the Sommerfeld ratio C_{p}(T)/T at low temperatures. Below 4 K χ(T), C_{p}(T)/T and ρ(T) can be described by χ(T) ∝ T^{-0.48}, C_{p}(T)/T ∝ √T and ρ(T) ∝ c ln(T)+AT^{3/2}, respectively. These observations provide an evidence that URu_{0.68}Pd_{0.32}Ge is a moderately heavy-fermion system with an electronic ground state of non-Fermi liquid character. We found non-linear effect of the magnetization and a large value of the Wilson ratio, which are consistent with the interpretation in terms of magnetic instability.
9
Content available remote

Synthesis and Characterization of the Superconductor Mo_3Sb_7

64%
Tran V., Bukowski Z.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
67-74
EN
We synthesized a polycrystalline sample of the superconductor Mo_3Sb_7 and characterized its basic properties by measurements of magnetization, electrical resistivity and specific heat. The measurements establish a superconducting phase transition at T_c=2.25 (0.05) K. In applied magnetic fields, the magnetization and resistivity show the behavior of type-II superconductor. From the specific heat measurement, the electronic specific heat coefficient,γ, specific heat jump at T_c, ΔC(T_c)/γT_c, and the Debye temperature Θ_D, are evaluated to be 34.5 mJ/(mol K^2), 1.56 and 283 K, respectively. From analysis of the specific heat data we suggest that this compound belongs to an intermediate strong coupling regime in the BCS context. The observed enhancement in theγ-value suggests a substantial contribution of Mo-4d-electrons to the density of states. Our experimental data do not support interpretation of superconductivity in Mo_3Sb_7 in terms of neither unconventional superconductivity or spin fluctuations proposed previously.
10
Content available remote

Transport Properties of the U_{1-x}Th_{x}Pt System

64%
Tran V., Troć R.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 3
399-402
EN
We present the results of measurements of electrical resistivity (ρ(T)) and magnetoresistance (Δϱ/ϱ_{0}(T)) on the solid solutions U_{1-x}Th_{x}Pt (x=0-0.8). The Curie temperature (T_{c}=21 K) found for the parent compound UPt, is steadily reduced upon the Th-substitution. The ρ(T) and Δϱ/ϱ_{0}(T) functions provide evidence of electron scattering due to spin fluctuations. The most interesting feature of Δϱ/ϱ_{0} is its high value of about -22% found for UPt and U_{0.9}Th_{0.1}Pt at their T_{c} and B=8 T. For samples with x ≥ 0.2, the value of Δϱ/ϱ_{0} at 4 K and 8 T increases with x and becomes positive for Th-composition x >= 0.6.
11
Content available remote

Influence of Yttrium Substitution οn the Electronic Structure and Magnetic Moment οf Gd_{7-x}Y_{x}Pd_{3} (x = 0, 1, 2, 3, 4)

51%
Klimczak M., Talik E., Tran V.
Acta Physica Polonica A
|
2009
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vol. 115
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issue 1
200-202
EN
The electronic structure and magnetic properties of Gd_{7-x}Y_{x}Pd_{3} (x = 0, 1, 2, 4) single crystals were examined. These compounds crystallized in the same crystal structure type (Th_{7}Fe_{3}) with the same c/a ratio of 0.63. A strongly anisotropic behavior of the magnetic and transport properties was found. Magnetic frustration and spin fluctuations on the palladium atoms are responsible for the complex magnetic properties of this ternary compound. As a part of current research we presented further characteristic of the Gd_{7-x}Y_{x}Pd_{3} (x = 0, 1, 2, 4) single crystal.
12
Content available remote

Magnetic Properties of URu_{1-x}Pd_{x}Ge Solid Solutions

51%
Gralak D., Zaleski A., Tran V.
|
|
vol. 126
|
issue 1
314-315
EN
The magnetic properties of the solid solutions URu_{1-x}Pd_{x}Ge with x = 0.1 - 0.9, crystallizing in the orthorhombic TiNiSi-type structure, were investigated by ac magnetic susceptibility and dc magnetization measurements. The experimental data reveal that there are three different regions of magnetic behaviour. A nonmagnetic ground state occurs for x < 0.3, however, as the Pd concentration is increased, the antiferromagnetism is stabilized for x=0.35 - 0.8, and two successive transitions, antiferro- and ferromagnetic, emerge in the x=0.9 composition.
13
Content available remote

Magnetic Phase Transition in CePd_{2}P_{2}

51%
Tran V., Bukowski Z., Tran L., Zaleski A.
|
|
vol. 126
|
issue 1
334-335
EN
The tetragonal CePd_{2}P_{2} compound has been investigated by ac magnetic susceptibility and dc magnetization measurements. The experimental data reveal a ferromagnetic phase transition at T_{C}=28.4± 0.2 K. Using Arrot-Noakes plot and scaling laws for a second-order phase transition, critical exponents for the ferromagnetic transition in the system were obtained. The critical exponents are located between those of the mean field and Heisenberg model values.
14
Content available remote

Thermoelectric Power of CeNi_4Si and YbNi_4Si Compounds

51%
Falkowski M., Kowalczyk A., Tran V., Miiller W.
Acta Physica Polonica A
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2008
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vol. 113
|
issue 1
303-306
EN
The thermoelectric power was measured from 4.2 to 300 K for CeNi_4Si and YbNi_4Si. The thermoelectric power was analysed in the framework of the phenomenological resonance model. According to the model the dominant contribution to thermopower is caused by scattering between electrons of a broad s-band and a narrow f-band with the Lorentzian shape. The electron-hole analogy is reflected in the thermoelectric power behaviour of the investigated compounds.
15
Content available remote

Anomalous Transport and Thermal Properties of the Solid Solutions U_{1-x}Th_{x}Cu_{5}M (M = Al, Ga, In and Sn)

51%
Troć R., Tran V., Kaczorowski D., Czopnik A.
Acta Physica Polonica A
|
2000
|
vol. 97
|
issue 1
25-35
EN
UCu_{5}M-type compounds are moderate heavy fermion systems with an antiferromagnetic order below T_{N} = 18, 16-25, and 25 K for M = Al, (Ga, In), and In, respectively, and a ferrimagnetic order with T_{C} = 54 K for M = Sn. We present the results of magnetoresistance measurements as a function of temperature and applied magnetic field for the pure compounds and for their solid solutions containing Th, i.e. U_{1-x}Th_{x}Cu_{5}M. Only in the case of UCu_{5}In a substantial positive contribution to the magnetoresistance was observed at low temperatures, as for normal antiferromagnets. For the Al- and Sn-based alloys the magnetoresistance at low temperatures is negative, and its field variation proves the existence of Kondo-type interactions. On Th-substitution the magnetic phase transition is shifted to lower temperature and simultaneously the magnetoresistance becomes less negative. The field dependence of the magnetoresistance of these alloys can be well described by the Coqblin-Schrieffer model. Interestingly, the heat capacity measurements have revealed a general tendency to increase the linear coefficient γ with magnetic dilution of a given UCu_{5}M compound by Th-substitution. This feature reflects an enlargement of the effective mass of conduction electrons with the increase in both the unit cell volume and magnetic dilution. Such a tendency is also observed for the system UCu_{5}(In_{1-x}Ga_{x}), though the unit cell is here suppressed with increasing x. Thus, a similar physical picture is reached in all these systems but involving probably different mechanisms.
16
Content available remote

Thermoelectric Power of the URu_{1-x}Pd_{x}Ge System

51%
Gralak D., Toliński T., Tran V.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 2
287-289
EN
We report the measurements of thermoelectric power, S(T), of the URu_{1-x}Pd_{x}Ge solid solutions in the temperature range 1.9-300 K. It is found that S(T) of URuGe is consistent with the behaviour of Kondo lattice, characterized by a low-temperature negative minimum and a high-temperature positive maximum. On the contrary, S(T) of the compositions 0.1 ≤ x ≤ 0.7 is negative over the whole temperature range measured and shows only one negative minimum around 200 K. The compositions x = 0.9 and 1, in addition to a high-temperature negative minimum, exhibit anomalies at low temperatures, presumably associated with the magnon drag. We interpret the experimental data assuming the presence of the Kondo and crystal-electric field effects.
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