Science and Technology of Advanced Materials, 2005
ABSTRACT A series of crystals of NaxTaS2 with different superconducting transition temperatures (... more ABSTRACT A series of crystals of NaxTaS2 with different superconducting transition temperatures (Tc) ranging from 2.0–4.4K were obtained by flux method. The structural data deduced from X-ray diffraction pattern shows that the sample has the same structure as 2H-TaS2. Compared with the resistivity curve of un-intercalated sample 2H-TaS2 (Tc=0.8K, TCDW≈70K), no signal of charge density wave (CDW) was observed in our present samples Na0.1TaS2. It is thus concluded that there is a competition between the superconductivity and the CDW. With the increase of sodium content, the rise of Tc in NaxTaS2 is caused mainly by the suppression to the CDW in 2H-TaS2, and the conventional rigid band model for layered dichalcogenide may be inadequate to explain the changes induced by the slight intercalation of sodium in 2H-TaS2.
We calculate the influence of a magnetic field on a transport property like the electrothermal co... more We calculate the influence of a magnetic field on a transport property like the electrothermal conductivity P of high-T c superconductors for either an anisotropic ͑or not͒ s-wave or a d x 2 Ϫy 2-wave gap parameter. The field dependence of the electrothermal conductivity of Bi 2 Sr 2 CaCu 2 O 8 , (BiPb͒ 2 Sr 2 Ca 2 Cu 3 O 10 , and Tl 2 Ba 2 CaCu 2 O 8 compounds near T c is then analyzed. It is shown that the behavior is consistent with a gap parameter of d x 2 Ϫy 2-wave type for reasonable values of the physical parameters and excludes an anisotropic ͑or not͒ s-wave symmetry over a temperature range extending up to T c. ͓S0163-1829͑96͒52542-7͔
Bulk amorphous alloys Fe-Al-Ga-P-B-Si were prepared by a single-roller melt spinning method. Elec... more Bulk amorphous alloys Fe-Al-Ga-P-B-Si were prepared by a single-roller melt spinning method. Electrical resistivity of alloys is of the order of 200 µOcm. The structural and magnetic components of resistivity are separated. The anomalous rise of resistivity during crystallization observed in Fe-Al-Ga-P-B-Si alloys with higher Si content is related to the precipitation of high resistivity crystalline phases. The strong exchange
The findings of Ghamlouch et al. [Phys. Rev. B 54, 9070 (1996)] on the jump in the thermoelectric... more The findings of Ghamlouch et al. [Phys. Rev. B 54, 9070 (1996)] on the jump in the thermoelectric power of high-Tc superconductors below the critical temperature in the presence of large magnetic fields are discussed. The complicated interplay between the vortex lattice thermodynamic transitions and the transport property percolation transitions raises questions on their similarities, differences, and relationships with respect to the (B,T) phase diagram features and the classical Kosterlitz-Thouless transition. A few comments pertain to the experimental details and others on the relevant role of thermomagnetic transport properties.
For the amorphous state of the nanocrystallizing alloys Fe73.5Cu1Nb3Si22_xBx the structural and m... more For the amorphous state of the nanocrystallizing alloys Fe73.5Cu1Nb3Si22_xBx the structural and magnetic contributions to the electrical resistivity were separated in the ferro-and paramagnetic intervals. The Curie tenlperature of amorphous alloys is close to 645 K and is only weakly affected by boron content. The anomalous resistivity behavior during first crystallization stage was discussed assuming conduction electron scattering on the grain boundaries. Crystallization rates for the first and second crystallization stages were determined.
Nominal Y0.3Ba0.6Na0.1CuO3- delta thin films were prepared with small grains having an orientatio... more Nominal Y0.3Ba0.6Na0.1CuO3- delta thin films were prepared with small grains having an orientation of the c axis perpendicular to the MgO substrate. The electrical resistivity and the thermoelectric power in the absence and in the presence of a magnetic field are reported. The magnetic field dependence of the irreversibility line is discussed. The role of the field for disentangling intragrain and intergrain effects in both coefficients is emphasized.
We have measured various transport properties, like the electrical resistivity, the thermoelectri... more We have measured various transport properties, like the electrical resistivity, the thermoelectric power, and the Nernst effect, in small or large magnetic fields, in various high temperature superconductors. We have observed that the area integral AQ of the excess magneto-transport quantities DQ(T,H) = Q(T,H)-Q(T,0) as a function of temperature obeys power laws like A(H) ~ Ha. The exponent seems to be related to the dimensionality of the system. We present theoretical conjectures for the findings.
Phase diagrams of d-wave superconductivity characterized by an order parameter coexisting with ch... more Phase diagrams of d-wave superconductivity characterized by an order parameter coexisting with charge-density waves (CDWs) characterized by an order parameter were constructed for the two-dimensional Fermi surface (FS) appropriate to, e.g., cuprates. CDWs were considered as an origin of the pseudogap appearing at antinodal FS sections of the d x 2 −y 2 superconductor. Two types of the-reentrance were found: with the temperature, T, and with the opening of the CDW sector, 2α. The angular plots in the momentum space for the resulting gap profile over the FS ('gap roses') were obtained. The gap patterns are rather involved, giving insight into the difficulties of the interpretation of photoemission spectra. It was shown that the-coexistence region exists even for the complete dielectric gapping due to the distinction between the superconducting and CDW order parameter symmetries. The checkerboard and unidirectional CDW configurations were examined, and both the phase diagrams and the behavior with T and α of the order parameters were found to differ. A more general case with a non-zero mismatch angle β between the superconducting lobes and the CDW sectors was analyzed, the case β = π/4 corresponding to the d xy symmetry of the superconducting order parameter. The phase diagrams were found to be sensitive to β-variations, showing that internal strains and external pressure can drastically affect the behavior of (T) and (T).
Single crystals of La1-xBaxMn1-yCoyO3 (0.26 leq x leq 0.37; 0 leq y leq 0.31) perovskites were gr... more Single crystals of La1-xBaxMn1-yCoyO3 (0.26 leq x leq 0.37; 0 leq y leq 0.31) perovskites were grown by the flux melt technique using the BaO-B2O3-BaF2 ternary system as a solvent. It was found that the cobalt content in the crystals is determined by the average oxidized state of the manganese ions and depends nonlinearly on the molar ratio of Co/Mn in the initial mixture. All the crystals exhibit ferromagnetic behaviour at low temperatures as well as a jump of resistivity and a magnetoresistance peak around the Curie temperature, gradually decreasing as the cobalt content increases. The low-temperature ferromagnetic phase transforms from the metallic to the semiconducting state with increase in cobalt content.
... Abstraet We report the electrical resistivity and thermoelectric power of polycrystalline Pb-... more ... Abstraet We report the electrical resistivity and thermoelectric power of polycrystalline Pb-dopedBi 3:223 superconductors. ... Composition analysis and x-ray diffraction patterns proved that the samples contained the Bi 2223 phase with negligible traces of other phases. ...
We compare structure and magnetic parameters of the polycrystalline and nanocrystalline manganite... more We compare structure and magnetic parameters of the polycrystalline and nanocrystalline manganites La 0.75 Ca 0.25 MnO 3 prepared by the carbonate precipitation and the sol-gel methods, respectively. The Curie temperature is surprisingly enhanced for nanocrystalline manganite. An effect of magnetic fields on transport parameters is analyzed for the metallic and semiconducting ranges.
Fe25A175 alloys synthesized from high-purity elements by means of the low-energy ball milling tec... more Fe25A175 alloys synthesized from high-purity elements by means of the low-energy ball milling technique have been characterized by X-ray diffraction, DSC and magnetization measurements. The alloys become amorphous after 600 h of milling. Prolonged milling for up to 800 h results in remarkable reductions in the magnetization and the exchange interaction.
Magnetization, electron transport, diffraction and calorimetric studies were performed on nanocry... more Magnetization, electron transport, diffraction and calorimetric studies were performed on nanocrystallizing alloys Fe76.5−xCu1NbxSi13.5B9 in a broad temperature range. The structural and magnetic contributions to electrical resistivity of amorphous alloys were separated. The decreasing of nanograins average size with rising Nb content was observed. The intra- and intergrain contributions to electrical resistivity were separated. The ϱ(T) variation agreed with the Mayadas-Shatzkes
The temperature and magnetic field dependence of the electrical resistivity of nickel near its Cu... more The temperature and magnetic field dependence of the electrical resistivity of nickel near its Curie temperature is calculated using a development of the de Gennes-Friedel model for spin-disorder resistivity that emphasizes the effect of spin correlations on sequential scattering events of point electrons rather than on the coherent scattering of conduction-electron wave packets. The calculated results are in good agreement with experimental data for nickel and explicitly display the complimentary roles of short-range and long-range orders in determining the dependence of the resistivity on temperature and magnetic field, respectively.
The nanocrystalline (mean grain size 20 nm) and microcrystalline magnetoresistive manganites with... more The nanocrystalline (mean grain size 20 nm) and microcrystalline magnetoresistive manganites with composition La0.7Ca0.3MnO3 were studied using a four probe electrical resistivity measurement in a strong magnetic field. The room temperature values of electrical resistivity are found to be 20 times larger for the nanocrystalline than for the microcrystalline sample, and therefore show a remarkable influence of fine grain microstructure. Such a difference reveals a more intense electron scattering inside the structurally and magnetically disordered grain boundaries in the nanocrystalline material than in the microcrystalline material. A pulsed magnetic field of 47 T reduces electrical resistivity three and eight times for the nano- and microcrystalline samples, respectively, and causes a monotonic shift of the transition temperature from TP=150 to 180 K in nanocrystalline manganite. In the microcrystalline sample TP shifts only from 250 to 270 K. The temperature dependencies of electr...
ABSTRACT Magnetic and structural investigation of Fe80Zn20 systems shows that various methods of ... more ABSTRACT Magnetic and structural investigation of Fe80Zn20 systems shows that various methods of mechanosynthesis result in fine structures with crystallite sizes between 20 and 100nm. All the systems studied exhibit strong magnetic ordering with Curie temperatures between 870 and 1000K. The coercive fields and magnetic energy losses are compared for various milling conditions.
The La 0.75 − x Gd x Ca 0.25 MnO 3 manganites with 0.0 ≤ x ≤ 0.75 are characterized by magnetic, ... more The La 0.75 − x Gd x Ca 0.25 MnO 3 manganites with 0.0 ≤ x ≤ 0.75 are characterized by magnetic, electrical resistivity and thermoelectric measurements. The isovalent Gd substitution causes that the metal-insulator transition is removed, whereas the negative magnetoresistance effect is weak. The electrical resistivity is described by the small polaron model.
The tunnel conductance G(V) for break junctions made of as-grown single-crystal Bi2Sr2CaCu2O8+δ s... more The tunnel conductance G(V) for break junctions made of as-grown single-crystal Bi2Sr2CaCu2O8+δ samples with Tc≈86–89K is measured, and clear-cut dip–hump structures are found in the range of bias voltage V=80–120mV. A theory of tunneling in symmetric junctions between inhomogeneous charge-density-wave (CDW) superconductors, considered in the framework of the s-pairing model, is developed. It is shown that CDWs are responsible for the appearance of the dip–hump structure in the tunnel current–voltage characteristics, and a proper description of the experimental results is obtained.
Science and Technology of Advanced Materials, 2005
ABSTRACT A series of crystals of NaxTaS2 with different superconducting transition temperatures (... more ABSTRACT A series of crystals of NaxTaS2 with different superconducting transition temperatures (Tc) ranging from 2.0–4.4K were obtained by flux method. The structural data deduced from X-ray diffraction pattern shows that the sample has the same structure as 2H-TaS2. Compared with the resistivity curve of un-intercalated sample 2H-TaS2 (Tc=0.8K, TCDW≈70K), no signal of charge density wave (CDW) was observed in our present samples Na0.1TaS2. It is thus concluded that there is a competition between the superconductivity and the CDW. With the increase of sodium content, the rise of Tc in NaxTaS2 is caused mainly by the suppression to the CDW in 2H-TaS2, and the conventional rigid band model for layered dichalcogenide may be inadequate to explain the changes induced by the slight intercalation of sodium in 2H-TaS2.
We calculate the influence of a magnetic field on a transport property like the electrothermal co... more We calculate the influence of a magnetic field on a transport property like the electrothermal conductivity P of high-T c superconductors for either an anisotropic ͑or not͒ s-wave or a d x 2 Ϫy 2-wave gap parameter. The field dependence of the electrothermal conductivity of Bi 2 Sr 2 CaCu 2 O 8 , (BiPb͒ 2 Sr 2 Ca 2 Cu 3 O 10 , and Tl 2 Ba 2 CaCu 2 O 8 compounds near T c is then analyzed. It is shown that the behavior is consistent with a gap parameter of d x 2 Ϫy 2-wave type for reasonable values of the physical parameters and excludes an anisotropic ͑or not͒ s-wave symmetry over a temperature range extending up to T c. ͓S0163-1829͑96͒52542-7͔
Bulk amorphous alloys Fe-Al-Ga-P-B-Si were prepared by a single-roller melt spinning method. Elec... more Bulk amorphous alloys Fe-Al-Ga-P-B-Si were prepared by a single-roller melt spinning method. Electrical resistivity of alloys is of the order of 200 µOcm. The structural and magnetic components of resistivity are separated. The anomalous rise of resistivity during crystallization observed in Fe-Al-Ga-P-B-Si alloys with higher Si content is related to the precipitation of high resistivity crystalline phases. The strong exchange
The findings of Ghamlouch et al. [Phys. Rev. B 54, 9070 (1996)] on the jump in the thermoelectric... more The findings of Ghamlouch et al. [Phys. Rev. B 54, 9070 (1996)] on the jump in the thermoelectric power of high-Tc superconductors below the critical temperature in the presence of large magnetic fields are discussed. The complicated interplay between the vortex lattice thermodynamic transitions and the transport property percolation transitions raises questions on their similarities, differences, and relationships with respect to the (B,T) phase diagram features and the classical Kosterlitz-Thouless transition. A few comments pertain to the experimental details and others on the relevant role of thermomagnetic transport properties.
For the amorphous state of the nanocrystallizing alloys Fe73.5Cu1Nb3Si22_xBx the structural and m... more For the amorphous state of the nanocrystallizing alloys Fe73.5Cu1Nb3Si22_xBx the structural and magnetic contributions to the electrical resistivity were separated in the ferro-and paramagnetic intervals. The Curie tenlperature of amorphous alloys is close to 645 K and is only weakly affected by boron content. The anomalous resistivity behavior during first crystallization stage was discussed assuming conduction electron scattering on the grain boundaries. Crystallization rates for the first and second crystallization stages were determined.
Nominal Y0.3Ba0.6Na0.1CuO3- delta thin films were prepared with small grains having an orientatio... more Nominal Y0.3Ba0.6Na0.1CuO3- delta thin films were prepared with small grains having an orientation of the c axis perpendicular to the MgO substrate. The electrical resistivity and the thermoelectric power in the absence and in the presence of a magnetic field are reported. The magnetic field dependence of the irreversibility line is discussed. The role of the field for disentangling intragrain and intergrain effects in both coefficients is emphasized.
We have measured various transport properties, like the electrical resistivity, the thermoelectri... more We have measured various transport properties, like the electrical resistivity, the thermoelectric power, and the Nernst effect, in small or large magnetic fields, in various high temperature superconductors. We have observed that the area integral AQ of the excess magneto-transport quantities DQ(T,H) = Q(T,H)-Q(T,0) as a function of temperature obeys power laws like A(H) ~ Ha. The exponent seems to be related to the dimensionality of the system. We present theoretical conjectures for the findings.
Phase diagrams of d-wave superconductivity characterized by an order parameter coexisting with ch... more Phase diagrams of d-wave superconductivity characterized by an order parameter coexisting with charge-density waves (CDWs) characterized by an order parameter were constructed for the two-dimensional Fermi surface (FS) appropriate to, e.g., cuprates. CDWs were considered as an origin of the pseudogap appearing at antinodal FS sections of the d x 2 −y 2 superconductor. Two types of the-reentrance were found: with the temperature, T, and with the opening of the CDW sector, 2α. The angular plots in the momentum space for the resulting gap profile over the FS ('gap roses') were obtained. The gap patterns are rather involved, giving insight into the difficulties of the interpretation of photoemission spectra. It was shown that the-coexistence region exists even for the complete dielectric gapping due to the distinction between the superconducting and CDW order parameter symmetries. The checkerboard and unidirectional CDW configurations were examined, and both the phase diagrams and the behavior with T and α of the order parameters were found to differ. A more general case with a non-zero mismatch angle β between the superconducting lobes and the CDW sectors was analyzed, the case β = π/4 corresponding to the d xy symmetry of the superconducting order parameter. The phase diagrams were found to be sensitive to β-variations, showing that internal strains and external pressure can drastically affect the behavior of (T) and (T).
Single crystals of La1-xBaxMn1-yCoyO3 (0.26 leq x leq 0.37; 0 leq y leq 0.31) perovskites were gr... more Single crystals of La1-xBaxMn1-yCoyO3 (0.26 leq x leq 0.37; 0 leq y leq 0.31) perovskites were grown by the flux melt technique using the BaO-B2O3-BaF2 ternary system as a solvent. It was found that the cobalt content in the crystals is determined by the average oxidized state of the manganese ions and depends nonlinearly on the molar ratio of Co/Mn in the initial mixture. All the crystals exhibit ferromagnetic behaviour at low temperatures as well as a jump of resistivity and a magnetoresistance peak around the Curie temperature, gradually decreasing as the cobalt content increases. The low-temperature ferromagnetic phase transforms from the metallic to the semiconducting state with increase in cobalt content.
... Abstraet We report the electrical resistivity and thermoelectric power of polycrystalline Pb-... more ... Abstraet We report the electrical resistivity and thermoelectric power of polycrystalline Pb-dopedBi 3:223 superconductors. ... Composition analysis and x-ray diffraction patterns proved that the samples contained the Bi 2223 phase with negligible traces of other phases. ...
We compare structure and magnetic parameters of the polycrystalline and nanocrystalline manganite... more We compare structure and magnetic parameters of the polycrystalline and nanocrystalline manganites La 0.75 Ca 0.25 MnO 3 prepared by the carbonate precipitation and the sol-gel methods, respectively. The Curie temperature is surprisingly enhanced for nanocrystalline manganite. An effect of magnetic fields on transport parameters is analyzed for the metallic and semiconducting ranges.
Fe25A175 alloys synthesized from high-purity elements by means of the low-energy ball milling tec... more Fe25A175 alloys synthesized from high-purity elements by means of the low-energy ball milling technique have been characterized by X-ray diffraction, DSC and magnetization measurements. The alloys become amorphous after 600 h of milling. Prolonged milling for up to 800 h results in remarkable reductions in the magnetization and the exchange interaction.
Magnetization, electron transport, diffraction and calorimetric studies were performed on nanocry... more Magnetization, electron transport, diffraction and calorimetric studies were performed on nanocrystallizing alloys Fe76.5−xCu1NbxSi13.5B9 in a broad temperature range. The structural and magnetic contributions to electrical resistivity of amorphous alloys were separated. The decreasing of nanograins average size with rising Nb content was observed. The intra- and intergrain contributions to electrical resistivity were separated. The ϱ(T) variation agreed with the Mayadas-Shatzkes
The temperature and magnetic field dependence of the electrical resistivity of nickel near its Cu... more The temperature and magnetic field dependence of the electrical resistivity of nickel near its Curie temperature is calculated using a development of the de Gennes-Friedel model for spin-disorder resistivity that emphasizes the effect of spin correlations on sequential scattering events of point electrons rather than on the coherent scattering of conduction-electron wave packets. The calculated results are in good agreement with experimental data for nickel and explicitly display the complimentary roles of short-range and long-range orders in determining the dependence of the resistivity on temperature and magnetic field, respectively.
The nanocrystalline (mean grain size 20 nm) and microcrystalline magnetoresistive manganites with... more The nanocrystalline (mean grain size 20 nm) and microcrystalline magnetoresistive manganites with composition La0.7Ca0.3MnO3 were studied using a four probe electrical resistivity measurement in a strong magnetic field. The room temperature values of electrical resistivity are found to be 20 times larger for the nanocrystalline than for the microcrystalline sample, and therefore show a remarkable influence of fine grain microstructure. Such a difference reveals a more intense electron scattering inside the structurally and magnetically disordered grain boundaries in the nanocrystalline material than in the microcrystalline material. A pulsed magnetic field of 47 T reduces electrical resistivity three and eight times for the nano- and microcrystalline samples, respectively, and causes a monotonic shift of the transition temperature from TP=150 to 180 K in nanocrystalline manganite. In the microcrystalline sample TP shifts only from 250 to 270 K. The temperature dependencies of electr...
ABSTRACT Magnetic and structural investigation of Fe80Zn20 systems shows that various methods of ... more ABSTRACT Magnetic and structural investigation of Fe80Zn20 systems shows that various methods of mechanosynthesis result in fine structures with crystallite sizes between 20 and 100nm. All the systems studied exhibit strong magnetic ordering with Curie temperatures between 870 and 1000K. The coercive fields and magnetic energy losses are compared for various milling conditions.
The La 0.75 − x Gd x Ca 0.25 MnO 3 manganites with 0.0 ≤ x ≤ 0.75 are characterized by magnetic, ... more The La 0.75 − x Gd x Ca 0.25 MnO 3 manganites with 0.0 ≤ x ≤ 0.75 are characterized by magnetic, electrical resistivity and thermoelectric measurements. The isovalent Gd substitution causes that the metal-insulator transition is removed, whereas the negative magnetoresistance effect is weak. The electrical resistivity is described by the small polaron model.
The tunnel conductance G(V) for break junctions made of as-grown single-crystal Bi2Sr2CaCu2O8+δ s... more The tunnel conductance G(V) for break junctions made of as-grown single-crystal Bi2Sr2CaCu2O8+δ samples with Tc≈86–89K is measured, and clear-cut dip–hump structures are found in the range of bias voltage V=80–120mV. A theory of tunneling in symmetric junctions between inhomogeneous charge-density-wave (CDW) superconductors, considered in the framework of the s-pairing model, is developed. It is shown that CDWs are responsible for the appearance of the dip–hump structure in the tunnel current–voltage characteristics, and a proper description of the experimental results is obtained.
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Papers by Marek Pękała