H. Szymczak - Independent Researcher (original) (raw)
Papers by H. Szymczak
Magnetic Ordering of Dy 3+ Ions in RbDy(WO 4 ) 2 Single Crystal
Journal of Low Temperature Physics
The specific heat C(T) of the monoclinic RbDy(WO4)2crystal has been studied at very low temperatu... more The specific heat C(T) of the monoclinic RbDy(WO4)2crystal has been studied at very low temperatures 0.2=T=1.9 K and in magnetic fields 0=H=0.38 T. The Neel temperature was shown to be equal to TN = 0.818 ± 0.005 K. The experimental value of the effective exchange parameter was obtained to be equal to J/k = - 0.798 K. The C T) dependence below Neel temperature 0.5TN0.99TN) is well described by 2D Ising model, whereas in the temperature region close above TN(1.01 TN2TN) it can be described by neither 2D, nor 3D Ising model. The experimental and theoretical H-TNdiagrams for fieldH ? aare in a reasonable agreement for simple quadratic lattice.
A Study of Spin-Phonon Interactions by Spin-Lattice Relaxation Processes
Phonon Scattering in Solids, 1976
When a particular transition in a paramagnetic impurity has been saturated, the return to thermal... more When a particular transition in a paramagnetic impurity has been saturated, the return to thermal equilibrium with the lattice does not necessarily follow a simple exponential. Even when it does the relaxation time τ1 so defined cannot usually be predicted by theory, one problem being to take adequate account of the lattice dynamics. The situation is often even more complicated when the ground state of the monitored ion is not a simple doublet and when other impurities are present in the sample. The return to thermal equilibrium is then seriously affected by cross relaxation both within the monitored spin system and also to other fast relaxing ions. In such a situation it is not easy to relate the τ1 measured experimentally to particular spin-lattice transition probabilities.
Phase separation in oxygen-doped cuprates
Phase Transitions, 1996
Experimental investigations of phase separation in high-Tc cuprates are reviewed with special emp... more Experimental investigations of phase separation in high-Tc cuprates are reviewed with special emphasis on recent results obtained on doped La2CuO4+x single crystals. Particular attention is paid to the magnetic properties. The experiments give very strong evidence that magnetic polarons are responsible for macroscopic phase separation observed in La2CuO4+x for x>0.
Low Temperature Physics, 2002
The following sequence of phase transformations is observed in the Nd 0.6 Ca 0.4 (Mn 1Ϫx Cr x )O ... more The following sequence of phase transformations is observed in the Nd 0.6 Ca 0.4 (Mn 1Ϫx Cr x )O 3 system: antiferromagnet (xϭ0), mixed magnetic state (0.015рxр0.04), ferrimagnet (0.04рxр0.8), and spin glass (xϭ1). At chromium concentrations near xϳ0.5 the Ne ´el temperature increases sharply, and the contribution from the Nd sublattice increases substantially. Since the chromium and manganese ions have a tendency to order, these results can be interpreted in a model of superexchange interactions.
Magnetocaloric effect in polycrystalline La based manganites modified with Sr
Journal of Physics: Conference Series, 2011
All In this paper, we present magnetocaloric properties of the polycrystalline La0.7Ca0.25Sr0,05M... more All In this paper, we present magnetocaloric properties of the polycrystalline La0.7Ca0.25Sr0,05MnO3 compound prepared by the ceramic method. X-ray diffraction indicated a single-phase compound with a perovskite structure. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. DeltaS was found to reduce from 8 J/kgK to
Journal of Magnetism and Magnetic Materials, 1992
Visual observations of magnetic flux profile and dc magnetization measurements have been performe... more Visual observations of magnetic flux profile and dc magnetization measurements have been performed for Bi2Sr2CaCu20 x superconducting single crystals before and after fast neutron irradiation. The critical current enhancement and the decrease of lower critical field was determined.
Photoinduced changes in the ferromagnetic resonance of CdCr2Se4 single crystals
Journal of Magnetism and Magnetic Materials, 1992
ABSTRACT The effect of light irradiation on the ferromagnetic resonance of CdCr2Se4 single crysta... more ABSTRACT The effect of light irradiation on the ferromagnetic resonance of CdCr2Se4 single crystals have been investigated in the temperature range from 4.2 to 130 K. It was found that the irradiation induced appreciable changes in microwave conductivity, FMR lineshape and magnetocrystalline anisotropy of this material. These findings are discussed in terms of the possible light-induced creation of Cr2+ centres in the crystal.
Spin glass like behavior of magnetization in anion substituted CuCr2Se4 magnetic semiconductor
Journal of Magnetism and Magnetic Materials, 1995
ABSTRACT
Field-induced phase transitions in Bi2CuO4
Journal of Magnetism and Magnetic Materials, 1995
ABSTRACT
Journal of Experimental and Theoretical Physics, 2006
Magnetic, electric, and elastic properties of the crystal and magnetic structure of double layere... more Magnetic, electric, and elastic properties of the crystal and magnetic structure of double layered perovskite NdBaCo 2 O 5.50 + δ are studied by the neutron diffraction method at various temperatures. The data are analyzed using two models of crystal structure. In the first model, the sample consists of two crystal-structure phases with ordered and disordered arrangements of oxygen vacancies. In the second model, a new crystalstructure phase is formed in this compound, which is characterized by ordering of oxygen vacancies in the plane of the rare-earth ion in the 1 c crystallographic position (0, 0, 1/2) of space group Pmmm. Two crystal-structure models correspond to different types of magnetic ordering (a mixture of a ferromagnetic phase and a G-type antiferromagnetic phase is presumed in the two-phase crystal-structure model, while a canted antiferromagnetic structure is presumed in the one-phase crystal structure model). The behavior of electric and elastic parameters is better described in the first model, while neutron diffraction studies are in better agreement with the second model.
Photoemission band structure of La0.7(Ca, Ce)0.3MnO3 thin films and a La0.9Ca0.1CoO3 crystal
Journal of Alloys and Compounds, 2007
The electron photoemission spectra of the valence bands of the manganese perovskite thin films La... more The electron photoemission spectra of the valence bands of the manganese perovskite thin films La0.7(Ca, Ce)0.3MnO3 and a cobaltite crystal La0.9Ca0.1CoO3 by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at room temperature were measured and analysed. The common feature of the ARUPS spectra was the two-peak structure between −3.5 and −7.0eV. Strong emission at about −1.0eV was detected only for the
The European Physical Journal B, 2007
The electron paramagnetic resonance (EPR) of Yb 3+ ions in a KY(WO4)2 single crystal was investig... more The electron paramagnetic resonance (EPR) of Yb 3+ ions in a KY(WO4)2 single crystal was investigated at T = 4.2 K and fixed frequency of 9.38 GHz. The resonance absorption observed on the lowest Kramers doublet represents the complex superposition of three spectra, corresponding to the ytterbium isotopes with different nuclear moments. The EPR spectrum is characterized by a strong anisotropy of the g-factors. The temperature dependence of the g-factors is shown to be caused by the strong spin-orbital and orbital-lattice coupling. The resonance lines broaden with increasing temperature due to the short spin-lattice relaxation times.
Structural units of cuprates in natural Cu-oxysalts
Acta Crystallographica Section A Foundations of Crystallography, 2001
The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme de... more The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme developed earlier for synthetic cuprates. The copper-oxygen compounds were considered as the salts of hypothetical copper acids with characteristic Cu-containing structural units of various dimensions formed by a polymerization of the CuO squares. The results of magnetic susceptibility measurements performed recently were analyzed from the viewpoint of the developed extended structural classification scheme. The dimerization of magnetic moments was considered as a property of cuprates which was strongly dependent on the type of Cu-containing structural unit. A further extension of the structural classification scheme for cuprates is also discussed.
physica status solidi (a), 2003
Studies of the magnetic properties of LaMn 1-x Co x O 3 (x = 0.18, 0.36, 0.54) single crystals gr... more Studies of the magnetic properties of LaMn 1-x Co x O 3 (x = 0.18, 0.36, 0.54) single crystals grown by the electrodeposition method are presented. Magnetization measurements versus temperature and magnetic field are performed in the temperature range from 5 to 300 K and in fields up to 5 T. It is shown that the thermomagnetic irreversibility between M FC (T) and M ZFC (T), the values of the magnetic moments of the Co ions, the large positive values of the paramagnetic Curie temperature, the hysteretic character of the M(H) loops, and the large values of the coercive field at low temperatures indicate the dominance of ferromagnetic interactions in these crystals. The results of measurements are analyzed in the framework of the two-phase magnetic state model in the crystal. The blocking temperature, the volume and the number of clusters are estimated for all the crystals studied.
Comparative study of the pressure effect on critical parameters of GdBa2Cu4O8 and YBa2Cu4O8
Physica C: Superconductivity, 1995
The influence of hydrostatic pressure up to 1.1 GPa on critical parameters (Tc, Hc1, jc) of YBa2C... more The influence of hydrostatic pressure up to 1.1 GPa on critical parameters (Tc, Hc1, jc) of YBa2Cu4O8 (Y124) and GdBa2Cu4O8 (Gd124) ceramics has been investigated using a CuBe pressure bomb. A linear of Tc with the growth of pressure was found, with dTc/dp = 5.5 K/GPa and 4.5 K/GPa for Y124 and Gd124, respectively. The difference in Tc increase on
Comparison of magnetocaloric properties of the Mn 2−x Fe x P 0.5 As 0.5 ( x = 1.0 and 0.7) compounds
Solid State Sciences, 2014
ABSTRACT The Mn2-xFexP0.5As0.5 compounds (x = 0.7 and 1.0) studied exhibit the magnetic phase tra... more ABSTRACT The Mn2-xFexP0.5As0.5 compounds (x = 0.7 and 1.0) studied exhibit the magnetic phase transitions, which are accompanied by a magnetic entropy change. For x = 1 the PM FM transition is of the first order one with a weak (2-3 K) thermal hysteresis in the vicinity of T-C = 275 K. The Mn1.3Fe0.7P0.5As0.5 compound possesses two magnetic transitions: the second-order PM FM transition at T-C = 190 K, followed by the FM-AFM transition at T-N = 90 K, leading to normal and inverse magnetocaloric effects, respectively. The maximum values of magnetic entropy change are equal to 17 J kg(-1) K-1 in MnFeP0.5As0.5 and 5 J kg(-1) K-1 in Mn1.3Fe0.7P0.5As0.5 for a field change of 5 T. The magnetic entropy changes were calculated using both the isofield magnetization curves versus temperature and the isothermal magnetization curves versus applied magnetic field. The magnetocaloric effect in MnFeAs0.5P0.5 is discussed in the terms of both the thermodynamic Maxwell relation and the Clausius-Clapeyron equation.
Intercalation-induced phase separation in oxygen deficient YBa2Cu3O6.51
Physica B: Condensed Matter, 1997
Abstract Intercalation of Li and Na into oxygen-deficient YBa2Cu3O6.51 samples has been studied. ... more Abstract Intercalation of Li and Na into oxygen-deficient YBa2Cu3O6.51 samples has been studied. Magnetization measurements of the intercalated samples were carried out as a function of temperature and magnetic field. The analysis of experimental results indicate the existence of the macroscopic phase separation into a nonmetallic phase with high Li (Na) concentration and a metallic phase with low Li (Na) concentration.
Reversible magnetization of radiation-disordered YBa2Cu3O7-x single crystals
Physical Review B, 1994
Single crystals of YBa2Cu3O7 were exposed to fast neutron irradiation with fluences up to 1019 n/... more Single crystals of YBa2Cu3O7 were exposed to fast neutron irradiation with fluences up to 1019 n/cm2 (E>0.1 MeV). Ac and dc magnetization measurements were performed to study the influence of irradiation-induced defects on the intrinsic and extrinsic parameters of superconductors. It has been shown that the observed increase of the anisotropy of the lower critical field in irradiated samples is due to the suppression of the Bean-Livingston surface barrier. Drastic changes of intrinsic parameters of YBa2Cu3O7 single crystals are interpreted within the framework of existing theoretical models.
Thin Solid Films, 2009
Penetration of electromagnetic waves through thin films of La 0.67 Sr 0.33 MnO 3 manganite grown ... more Penetration of electromagnetic waves through thin films of La 0.67 Sr 0.33 MnO 3 manganite grown by pulsed laser deposition on (100) SrTiO 3 and LaAlO 3 substrates was investigated and compared to the data obtained for the bulk specimens of the same composition. Experiments were carried out in the frequency range from 50 kHz to 20 MHz. Strong frequency-dependent variations of penetration coefficient in the static magnetic field were observed both for ferromagnetic and paramagnetic temperatures. The experimental data obtained confirm preservation of a local dynamic magnetic ordering in the paramagnetic temperature range by 1.10 to 1.22 times higher than the Curie temperature. The value of upper frequency limit of the dynamic polaron correlations in the paramagnetic phase was obtained.
Anisotropy of magnetic properties of a twin-free EuBaCo2O5.5 single crystal
Physics of the Solid State, 2007
ABSTRACT The magnetic characteristics of a twin-free EuBaCo2O5.5 single crystal were studied. It ... more ABSTRACT The magnetic characteristics of a twin-free EuBaCo2O5.5 single crystal were studied. It is shown that Co ions exhibit an Ising-type behavior with an easy axis directed along the a axis in the temperature range from 2 K to T c (250 K). As the temperature decreases from 300 K, a number of magnetic phase transitions occur under magnetic fields H ∥ a. In the range where antiferromagnetic ordering of Co3+ ions exists, metamagnetic transitions were observed to occur in fields whose values were dependent on temperature. The strengths of competing interactions in the crystal are estimated.
Magnetic Ordering of Dy 3+ Ions in RbDy(WO 4 ) 2 Single Crystal
Journal of Low Temperature Physics
The specific heat C(T) of the monoclinic RbDy(WO4)2crystal has been studied at very low temperatu... more The specific heat C(T) of the monoclinic RbDy(WO4)2crystal has been studied at very low temperatures 0.2=T=1.9 K and in magnetic fields 0=H=0.38 T. The Neel temperature was shown to be equal to TN = 0.818 ± 0.005 K. The experimental value of the effective exchange parameter was obtained to be equal to J/k = - 0.798 K. The C T) dependence below Neel temperature 0.5TN0.99TN) is well described by 2D Ising model, whereas in the temperature region close above TN(1.01 TN2TN) it can be described by neither 2D, nor 3D Ising model. The experimental and theoretical H-TNdiagrams for fieldH ? aare in a reasonable agreement for simple quadratic lattice.
A Study of Spin-Phonon Interactions by Spin-Lattice Relaxation Processes
Phonon Scattering in Solids, 1976
When a particular transition in a paramagnetic impurity has been saturated, the return to thermal... more When a particular transition in a paramagnetic impurity has been saturated, the return to thermal equilibrium with the lattice does not necessarily follow a simple exponential. Even when it does the relaxation time τ1 so defined cannot usually be predicted by theory, one problem being to take adequate account of the lattice dynamics. The situation is often even more complicated when the ground state of the monitored ion is not a simple doublet and when other impurities are present in the sample. The return to thermal equilibrium is then seriously affected by cross relaxation both within the monitored spin system and also to other fast relaxing ions. In such a situation it is not easy to relate the τ1 measured experimentally to particular spin-lattice transition probabilities.
Phase separation in oxygen-doped cuprates
Phase Transitions, 1996
Experimental investigations of phase separation in high-Tc cuprates are reviewed with special emp... more Experimental investigations of phase separation in high-Tc cuprates are reviewed with special emphasis on recent results obtained on doped La2CuO4+x single crystals. Particular attention is paid to the magnetic properties. The experiments give very strong evidence that magnetic polarons are responsible for macroscopic phase separation observed in La2CuO4+x for x>0.
Low Temperature Physics, 2002
The following sequence of phase transformations is observed in the Nd 0.6 Ca 0.4 (Mn 1Ϫx Cr x )O ... more The following sequence of phase transformations is observed in the Nd 0.6 Ca 0.4 (Mn 1Ϫx Cr x )O 3 system: antiferromagnet (xϭ0), mixed magnetic state (0.015рxр0.04), ferrimagnet (0.04рxр0.8), and spin glass (xϭ1). At chromium concentrations near xϳ0.5 the Ne ´el temperature increases sharply, and the contribution from the Nd sublattice increases substantially. Since the chromium and manganese ions have a tendency to order, these results can be interpreted in a model of superexchange interactions.
Magnetocaloric effect in polycrystalline La based manganites modified with Sr
Journal of Physics: Conference Series, 2011
All In this paper, we present magnetocaloric properties of the polycrystalline La0.7Ca0.25Sr0,05M... more All In this paper, we present magnetocaloric properties of the polycrystalline La0.7Ca0.25Sr0,05MnO3 compound prepared by the ceramic method. X-ray diffraction indicated a single-phase compound with a perovskite structure. The value of magnetocaloric effect has been determined from the measurements of magnetization as a function of temperature and an external magnetic field. DeltaS was found to reduce from 8 J/kgK to
Journal of Magnetism and Magnetic Materials, 1992
Visual observations of magnetic flux profile and dc magnetization measurements have been performe... more Visual observations of magnetic flux profile and dc magnetization measurements have been performed for Bi2Sr2CaCu20 x superconducting single crystals before and after fast neutron irradiation. The critical current enhancement and the decrease of lower critical field was determined.
Photoinduced changes in the ferromagnetic resonance of CdCr2Se4 single crystals
Journal of Magnetism and Magnetic Materials, 1992
ABSTRACT The effect of light irradiation on the ferromagnetic resonance of CdCr2Se4 single crysta... more ABSTRACT The effect of light irradiation on the ferromagnetic resonance of CdCr2Se4 single crystals have been investigated in the temperature range from 4.2 to 130 K. It was found that the irradiation induced appreciable changes in microwave conductivity, FMR lineshape and magnetocrystalline anisotropy of this material. These findings are discussed in terms of the possible light-induced creation of Cr2+ centres in the crystal.
Spin glass like behavior of magnetization in anion substituted CuCr2Se4 magnetic semiconductor
Journal of Magnetism and Magnetic Materials, 1995
ABSTRACT
Field-induced phase transitions in Bi2CuO4
Journal of Magnetism and Magnetic Materials, 1995
ABSTRACT
Journal of Experimental and Theoretical Physics, 2006
Magnetic, electric, and elastic properties of the crystal and magnetic structure of double layere... more Magnetic, electric, and elastic properties of the crystal and magnetic structure of double layered perovskite NdBaCo 2 O 5.50 + δ are studied by the neutron diffraction method at various temperatures. The data are analyzed using two models of crystal structure. In the first model, the sample consists of two crystal-structure phases with ordered and disordered arrangements of oxygen vacancies. In the second model, a new crystalstructure phase is formed in this compound, which is characterized by ordering of oxygen vacancies in the plane of the rare-earth ion in the 1 c crystallographic position (0, 0, 1/2) of space group Pmmm. Two crystal-structure models correspond to different types of magnetic ordering (a mixture of a ferromagnetic phase and a G-type antiferromagnetic phase is presumed in the two-phase crystal-structure model, while a canted antiferromagnetic structure is presumed in the one-phase crystal structure model). The behavior of electric and elastic parameters is better described in the first model, while neutron diffraction studies are in better agreement with the second model.
Photoemission band structure of La0.7(Ca, Ce)0.3MnO3 thin films and a La0.9Ca0.1CoO3 crystal
Journal of Alloys and Compounds, 2007
The electron photoemission spectra of the valence bands of the manganese perovskite thin films La... more The electron photoemission spectra of the valence bands of the manganese perovskite thin films La0.7(Ca, Ce)0.3MnO3 and a cobaltite crystal La0.9Ca0.1CoO3 by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at room temperature were measured and analysed. The common feature of the ARUPS spectra was the two-peak structure between −3.5 and −7.0eV. Strong emission at about −1.0eV was detected only for the
The European Physical Journal B, 2007
The electron paramagnetic resonance (EPR) of Yb 3+ ions in a KY(WO4)2 single crystal was investig... more The electron paramagnetic resonance (EPR) of Yb 3+ ions in a KY(WO4)2 single crystal was investigated at T = 4.2 K and fixed frequency of 9.38 GHz. The resonance absorption observed on the lowest Kramers doublet represents the complex superposition of three spectra, corresponding to the ytterbium isotopes with different nuclear moments. The EPR spectrum is characterized by a strong anisotropy of the g-factors. The temperature dependence of the g-factors is shown to be caused by the strong spin-orbital and orbital-lattice coupling. The resonance lines broaden with increasing temperature due to the short spin-lattice relaxation times.
Structural units of cuprates in natural Cu-oxysalts
Acta Crystallographica Section A Foundations of Crystallography, 2001
The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme de... more The structure of copper oxysalt minerals is analyzed on the basis of the classification scheme developed earlier for synthetic cuprates. The copper-oxygen compounds were considered as the salts of hypothetical copper acids with characteristic Cu-containing structural units of various dimensions formed by a polymerization of the CuO squares. The results of magnetic susceptibility measurements performed recently were analyzed from the viewpoint of the developed extended structural classification scheme. The dimerization of magnetic moments was considered as a property of cuprates which was strongly dependent on the type of Cu-containing structural unit. A further extension of the structural classification scheme for cuprates is also discussed.
physica status solidi (a), 2003
Studies of the magnetic properties of LaMn 1-x Co x O 3 (x = 0.18, 0.36, 0.54) single crystals gr... more Studies of the magnetic properties of LaMn 1-x Co x O 3 (x = 0.18, 0.36, 0.54) single crystals grown by the electrodeposition method are presented. Magnetization measurements versus temperature and magnetic field are performed in the temperature range from 5 to 300 K and in fields up to 5 T. It is shown that the thermomagnetic irreversibility between M FC (T) and M ZFC (T), the values of the magnetic moments of the Co ions, the large positive values of the paramagnetic Curie temperature, the hysteretic character of the M(H) loops, and the large values of the coercive field at low temperatures indicate the dominance of ferromagnetic interactions in these crystals. The results of measurements are analyzed in the framework of the two-phase magnetic state model in the crystal. The blocking temperature, the volume and the number of clusters are estimated for all the crystals studied.
Comparative study of the pressure effect on critical parameters of GdBa2Cu4O8 and YBa2Cu4O8
Physica C: Superconductivity, 1995
The influence of hydrostatic pressure up to 1.1 GPa on critical parameters (Tc, Hc1, jc) of YBa2C... more The influence of hydrostatic pressure up to 1.1 GPa on critical parameters (Tc, Hc1, jc) of YBa2Cu4O8 (Y124) and GdBa2Cu4O8 (Gd124) ceramics has been investigated using a CuBe pressure bomb. A linear of Tc with the growth of pressure was found, with dTc/dp = 5.5 K/GPa and 4.5 K/GPa for Y124 and Gd124, respectively. The difference in Tc increase on
Comparison of magnetocaloric properties of the Mn 2−x Fe x P 0.5 As 0.5 ( x = 1.0 and 0.7) compounds
Solid State Sciences, 2014
ABSTRACT The Mn2-xFexP0.5As0.5 compounds (x = 0.7 and 1.0) studied exhibit the magnetic phase tra... more ABSTRACT The Mn2-xFexP0.5As0.5 compounds (x = 0.7 and 1.0) studied exhibit the magnetic phase transitions, which are accompanied by a magnetic entropy change. For x = 1 the PM FM transition is of the first order one with a weak (2-3 K) thermal hysteresis in the vicinity of T-C = 275 K. The Mn1.3Fe0.7P0.5As0.5 compound possesses two magnetic transitions: the second-order PM FM transition at T-C = 190 K, followed by the FM-AFM transition at T-N = 90 K, leading to normal and inverse magnetocaloric effects, respectively. The maximum values of magnetic entropy change are equal to 17 J kg(-1) K-1 in MnFeP0.5As0.5 and 5 J kg(-1) K-1 in Mn1.3Fe0.7P0.5As0.5 for a field change of 5 T. The magnetic entropy changes were calculated using both the isofield magnetization curves versus temperature and the isothermal magnetization curves versus applied magnetic field. The magnetocaloric effect in MnFeAs0.5P0.5 is discussed in the terms of both the thermodynamic Maxwell relation and the Clausius-Clapeyron equation.
Intercalation-induced phase separation in oxygen deficient YBa2Cu3O6.51
Physica B: Condensed Matter, 1997
Abstract Intercalation of Li and Na into oxygen-deficient YBa2Cu3O6.51 samples has been studied. ... more Abstract Intercalation of Li and Na into oxygen-deficient YBa2Cu3O6.51 samples has been studied. Magnetization measurements of the intercalated samples were carried out as a function of temperature and magnetic field. The analysis of experimental results indicate the existence of the macroscopic phase separation into a nonmetallic phase with high Li (Na) concentration and a metallic phase with low Li (Na) concentration.
Reversible magnetization of radiation-disordered YBa2Cu3O7-x single crystals
Physical Review B, 1994
Single crystals of YBa2Cu3O7 were exposed to fast neutron irradiation with fluences up to 1019 n/... more Single crystals of YBa2Cu3O7 were exposed to fast neutron irradiation with fluences up to 1019 n/cm2 (E>0.1 MeV). Ac and dc magnetization measurements were performed to study the influence of irradiation-induced defects on the intrinsic and extrinsic parameters of superconductors. It has been shown that the observed increase of the anisotropy of the lower critical field in irradiated samples is due to the suppression of the Bean-Livingston surface barrier. Drastic changes of intrinsic parameters of YBa2Cu3O7 single crystals are interpreted within the framework of existing theoretical models.
Thin Solid Films, 2009
Penetration of electromagnetic waves through thin films of La 0.67 Sr 0.33 MnO 3 manganite grown ... more Penetration of electromagnetic waves through thin films of La 0.67 Sr 0.33 MnO 3 manganite grown by pulsed laser deposition on (100) SrTiO 3 and LaAlO 3 substrates was investigated and compared to the data obtained for the bulk specimens of the same composition. Experiments were carried out in the frequency range from 50 kHz to 20 MHz. Strong frequency-dependent variations of penetration coefficient in the static magnetic field were observed both for ferromagnetic and paramagnetic temperatures. The experimental data obtained confirm preservation of a local dynamic magnetic ordering in the paramagnetic temperature range by 1.10 to 1.22 times higher than the Curie temperature. The value of upper frequency limit of the dynamic polaron correlations in the paramagnetic phase was obtained.
Anisotropy of magnetic properties of a twin-free EuBaCo2O5.5 single crystal
Physics of the Solid State, 2007
ABSTRACT The magnetic characteristics of a twin-free EuBaCo2O5.5 single crystal were studied. It ... more ABSTRACT The magnetic characteristics of a twin-free EuBaCo2O5.5 single crystal were studied. It is shown that Co ions exhibit an Ising-type behavior with an easy axis directed along the a axis in the temperature range from 2 K to T c (250 K). As the temperature decreases from 300 K, a number of magnetic phase transitions occur under magnetic fields H ∥ a. In the range where antiferromagnetic ordering of Co3+ ions exists, metamagnetic transitions were observed to occur in fields whose values were dependent on temperature. The strengths of competing interactions in the crystal are estimated.