Journal of Experimental and Theoretical Physics Letters, 2002
ABSTRACT The electrical resistance and the thermoelectric power in the ab plane of a weakly oxyge... more ABSTRACT The electrical resistance and the thermoelectric power in the ab plane of a weakly oxygen-doped La2CuO4+x crystal (0.001<x<0.007) and its static magnetic susceptibility were studied in the vicinity of antiferromagnetic transition. The electrical resistance and the thermoelectric power behave anomalously near the Néel temperature, indicating that the transport is strongly affected by the establishment of long-range antiferromagnetic order. Analysis of the obtained data allows the conclusion to be drawn that the doping gives rise to a conduction band as a result of the overlap between the wave functions of deep impurity states that are strongly renormalized due to the correlation and polaron effects.
Nd3+ induced twofold continuous spin reorientation transition and magnetization along the b-axis in a Dy0.9Nd0.1FeO3 single crystal
CrystEngComm
An intriguing hybrid magnetic configuration Γ4+3 with non-zero spontaneous magnetization along b-... more An intriguing hybrid magnetic configuration Γ4+3 with non-zero spontaneous magnetization along b-axis was found in DNFO91 single crystal. Contributions of R3+ were distinguished and the relative strength can be manipulated with magnetic field.
Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroi... more Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroic NdMn2O5 has been performed using both non-polarized and polarized neutron diffraction techniques. Below TN ≈ 30.5 K magnetic Bragg reflections corresponding to the nonchiral type magnetic structure with propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted magnetic modulation with a similar vector kz2 occurs, which is attributed to the magnetization of the Nd 3+ ions by the Mn-sub-lattice. Strong temperature hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5 was observed depending on the cooling or heating history of the sample. Below about 20 K the magnetic structure became of a chiral type. From spherical neutron polarimetry measurements, the resulting low-temperature magnetic structure kz3 was approximated by the general elliptic helix. The parameters of the magnetic helix-like ellipticity and helical plane orientation in regard to the crystal structure were determined. A reorientation of the helix occurs at an intermediate temperature between 4 K and 18 K. A difference between the population of right-and left-handed chiral domains of about 0.2 was observed in the as-grown crystal when cooling without an external electric field. The magnetic chiral ratio can be changed by the application of an external electric field of a few kV/cm, revealing strong magnetoelectric coupling. A linear dependence of the magnetic chirality on the applied electric field in NdMn2O5 was found. The results are discussed within the frame of the antisymmetric super-exchange model for Dzyaloshinsky-Moria interaction. I.
[Ways to decrease the number of diagnostic errors and to improve the treatment results in acute appendicitis]
Vestnik khirurgii imeni I. I. Grekova, 1979
The investigation of 2114 patients admitted for acute appendicitis has shown that after an examin... more The investigation of 2114 patients admitted for acute appendicitis has shown that after an examination by the surgeon and the blood and urine tests the diagnosis of acute appendicitis was rejected in 922 patients (43%). Out of 1192 patients admitted to the hospital with the diagnosis of acute appendicitis 183 patients (15,4%) did not confirm the diagnosis of acute appendicitis after additional examination and observation of the patients.
... Louis Nel, Centre National de la Recherche Scientifique, 166X, 38042 Grenoble CEDEX, France I... more ... Louis Nel, Centre National de la Recherche Scientifique, 166X, 38042 Grenoble CEDEX, France IM Vitebsky Institut for Single Crystals, Ukranian Academy of Sciences, 310141 Kharkov, Ukraine A. Deville and B ... 9K. A. Kubat-Martin, Z. Fisk, and RR Ryan, Acta Crystal-logr. ...
Nuclear quadrupole resonance of barium in BaBiO3 and BaPbO3
Physical Review B, 2001
ABSTRACT The nuclear quadrupole resonance (NQR) on Ba nuclei was studied in four samples of BaBiO... more ABSTRACT The nuclear quadrupole resonance (NQR) on Ba nuclei was studied in four samples of BaBiO3 prepared in different ways and, in addition, in BaPbO3. The spectrum of 137Ba at T=4.2 K consists of a relatively broad line centered near 18 MHz for all BaBiO3 samples and near 13 MHz for BaPbO3. The integrated intensity of the 137Ba resonance in the ceramic sample of BaBiO3 synthesized at 800°C is approximately twice as large as that in ceramic samples and a single crystal prepared at 930–1080°C. The decrease of the NQR signal can be attributed to the partial disordering of charge-disproportionated Bi ions on the two inequivalent sites. The broadening of the resonance indicates that local distortions of the crystal structure exist in both compounds. The point-charge model was used to analyze the electric-field gradient on the Ba sites.
With the use of X-ray excited polar core-level and valence-band photoelectron-diffraction pattern... more With the use of X-ray excited polar core-level and valence-band photoelectron-diffraction patterns (XPED) and corresi~)ndmg energy distribution curves from TiO2(l10) (ruffle) along various azimuths in the surface plane, projected partial densities-of-states of the constituents in the valence band have been extracted. The results obtained from this angle-resolved method do not depend on the electron exit angle and seem to be a good measure for state densities of the bulk. A comparison with electronic structurt calculations is given.
Neutron diffraction studies of HoFeO3 single crystal were performed under external magnetic field... more Neutron diffraction studies of HoFeO3 single crystal were performed under external magnetic fields. The interplay between the external magnetic field, Dzyaloshinsky-Moria antisymmetric exchange and isotropic exchange interactions between Fe and Ho sublattice and inside Fe sublattice provides a rich phase diagram. As the result of the balance of exchange interactions inside crystal and external magnetic field we found 8 different magnetic phases, produced or suppressed by the field.
Neutron spectroscopy of 4f collective magnetic excitations in R 2 − x Ce x CuO 4 (R=Nd,Pr)
Physical Review B, 1997
We have studied the wave-vector dependence of the magnetic excitation spectrum of Nd in Nd 2-x Ce... more We have studied the wave-vector dependence of the magnetic excitation spectrum of Nd in Nd 2-x Ce x CuO 4 n (x= 0, 0.13) and of Pr in Pr 1.86 Ce 0.14 CuO 4 by inelastic neutron-scattering experiments on single crystals. The results are analyzed with the help of model ...
Raman study of crystal-field excitations in Pr2CuO4
Physical Review B, 1997
Raman measurements in a Pr2CuO4 single crystal show structures related to nine crystal-field (CF)... more Raman measurements in a Pr2CuO4 single crystal show structures related to nine crystal-field (CF) excitations. They correspond to transitions within the 3H4, 3H5, and 3H6 multiplets of Pr3+ ions in C4v site symmetry. Satellites to these CF excitations are also observed and associated with the presence of an inequivalent Pr3+ site of lower symmetry. A set of CF parameters which
Magnetic field switching of ferroelectricity in spiral magnet CuCrO2
ABSTRACT MARCH MEETING ABSTRACT: The triangular lattice antiferromagnet CuCrO2 show ferroelectric... more ABSTRACT MARCH MEETING ABSTRACT: The triangular lattice antiferromagnet CuCrO2 show ferroelectricity induced by a proper-screw spiral magnetic structure, where spins in form 120^o angles with neighboring spins due to frustration. CuCrO2 is thought to be a rare example of the Arima mechanism for multiferroic behavior. In addition, it has been shown that the magnetoelectric coupling can be tuned by both an electric and a magnetic field along ab-plane. We test a prediction for the magnetic field-evolution of the physical properties of CuCrO2 via magnetization and electric polarization measurements up to 65 T. We explore the complicated H-T phase diagram along different crystalline directions. In zero field, a spontaneous electric polarization in CuCrO2 is coupled to antiferromagnetic ordering below 24 K without an accompanying structural phase transition. In high fields, we observe electric polarization flops for magnetic fields applied along both the ab-plane and the c-axis, although at different magnetic fields than predicted. By contrast no noticeable anomaly is detected in magnetization isotherms, which are linear in fields up to 65 T. The electric polarization reversal is highly sensitive to the external magnetic field for both the ab-plane and c-axis due to a 3-dimensional proper-screw structure. We find that additional interactions may be necessary to explain our observed results.
The magnetization, resistivity and magnetoresistance (MR) of single crystals of GdBaCo 2 O 5.5 an... more The magnetization, resistivity and magnetoresistance (MR) of single crystals of GdBaCo 2 O 5.5 and EuBaCo 2 O 5.5 are measured over a wide range of dc magnetic fields (up to 30 T) and temperature. In LnBaCo 2 O 5.5 (Ln=Gd, Eu), the Co-ions are trivalent and can exist in three spin states, namely, the S=0 low spin state (LS), the S= 1 intermediate spin state (IS) and the S=2 high spin state (HS). We confirm that GdBaCo 2 O 5.5 and EuBaCo 2 O 5.5 have a metal-insulator transition accompanied by a spin-state transition at T MI ≈ 365 and 335 K, respectively. The data suggest an equal ratio of LS (S=0) and IS (S=1) Co 3+ ions below T MI , with no indication of additional spin state transitions. The low field magnetization shows a transition to a highly anisotropic ferromagnetic phase at 270 K, followed by another magnetic transition to an antiferromagnetic phase at a slightly lower temperature. The magnetization data are suggestive of weak correlations between the Gd-spins but no clear signature of ordering is seen for T > 2 K. Significant anisotropy between the a-b plane and c axis was observed in magnetic and magnetotransport properties for both compounds. For GdBaCo 2 O 5.5 , the resistivity and MR data imply a strong correlation between the spin-order and charge carriers. For EuBaCo 2 O 5.5 , the magnetic phase diagram is very similar to its Gd counterpart, but the low-T MR with current flow in the ab plane is positive rather than negative as for Gd. The magnitude and the hysteresis of the MR for EuBaCo 2 O 5.5 decrease with increasing temperature, and at higher T the MR changes sign and becomes negative. The difference
Observation of Cu 2 + spin resonance in Gd 2 CuO 4
Physical Review B, 1995
We report on the detection of Cu2+ spin resonance in a compound belonging to a family of electron... more We report on the detection of Cu2+ spin resonance in a compound belonging to a family of electron-doped high-temperature superconducting materials with general formula R2-xCexCuO4. Experiments were carried out on single Gd2CuO4 crystals at low temperatures using millimeter and far-infrared techniques combined with high magnetic fields. Three antiferromagnetic resonance branches are observed with the following frequency gaps at 2 K: omega1=0.8 cm-1, omega2=2.8 cm-1, Omega2=17 cm-1. The omega1 and omega2 frequencies correspond to the Gd magnetic subsystem. The characteristic field and temperature dependence of the Omega2 resonance allow us to identify it as the Cu spin resonance.
Competing Interactions in the $S$=3/2 Kagome Staircase Co$_{3}$V$_{2}$O$_{8}$: Evolution of the Commensurate and Incommensurate Phases in a Magnetic Field
Core-level photoemission and x-ray absorption study of Na-covered and oxygen-deficient Ba 0.6 K 0.4 BiO 3 − y single crystals
Physical Review B, 1998
ABSTRACT To study the effects of doping in Ba0.6K0.4BiO3, core-level and valence-band photoemissi... more ABSTRACT To study the effects of doping in Ba0.6K0.4BiO3, core-level and valence-band photoemission results are presented for a single crystal with various Na coverages and for an oxygen-deficient sample. It was found that the valence band and the Ba 4d, Ba 5p, Bi 5d, and O 1s core levels were shifted to higher binding energies with increasing Na coverage, consistent with an increase in band filling, whereas for K 2p, the shift was negligible. The valence band broadens as Na is deposited but the intensity at the Fermi level stays constant, in line with the n-type nature of the charge carriers in Ba1-xKxBiO3. The prepeak intensity in the O K edge absorption spectrum as well as the Bi 4f asymmetry were found to be lower for oxygen-deficient Ba0.6K0.4BiO3-y than for the stoichiometric samples, indicating the importance of oxygen content for metallic Ba0.6K0.4BiO3. The asymmetry of the Bi 4f increased with Na deposition, suggesting the growth of a high binding energy component with reduced valency, whereas the Ba 4d, Ba 5p, and K 2p became narrower, consistent with a decrease of the surface-core-level shifts.
ABSTRACT We have made neutron-diffraction, magnetization, and antiferromagnetic-resonance investi... more ABSTRACT We have made neutron-diffraction, magnetization, and antiferromagnetic-resonance investigations of Gd2CuO4 single crystals. Neutron-diffraction experiments on 158enriched Gd2CuO4 single crystals show that the gadolinium atoms order antiferromagnetically at TN=6.4 K with the propagation vector k=(0,0,0). The two Gd atoms of the primitive unit cell related by the center of symmetry are oppositely oriented. The antiferromagnetic-resonance spectra indicate that Gd2CuO4 belongs to the class of ‘‘easy-plane’’ antiferromagnets and show the presence of a second-order reorientation phase transition at Hc=0.88 T (H∥[100], T=1.8 K). The magnetization measurements confirm the presence of this reorientation transition and also show a complete ferromagnetic alignment of Gd moments at H=11 T and T=1.5 K.
Orbital fluctuating state in ferromagnetic insulating LaMnO3+δ (0.085⩽δ⩽0.125) studied using Raman spectroscopy
Physical Review B, 2006
K.-Y. Choi,1 Yu. G. Pashkevich,2 VP Gnezdilov,3 G. Güntherodt,4 AV Yeremenko,3 DA Nabok,2 VI Kame... more K.-Y. Choi,1 Yu. G. Pashkevich,2 VP Gnezdilov,3 G. Güntherodt,4 AV Yeremenko,3 DA Nabok,2 VI Kamenev,2 SN Barilo,5 SV Shiryaev,5 AG Soldatov,5 and P. Lemmens6 1Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan 2A. ...
Journal of Experimental and Theoretical Physics Letters, 2002
ABSTRACT The electrical resistance and the thermoelectric power in the ab plane of a weakly oxyge... more ABSTRACT The electrical resistance and the thermoelectric power in the ab plane of a weakly oxygen-doped La2CuO4+x crystal (0.001<x<0.007) and its static magnetic susceptibility were studied in the vicinity of antiferromagnetic transition. The electrical resistance and the thermoelectric power behave anomalously near the Néel temperature, indicating that the transport is strongly affected by the establishment of long-range antiferromagnetic order. Analysis of the obtained data allows the conclusion to be drawn that the doping gives rise to a conduction band as a result of the overlap between the wave functions of deep impurity states that are strongly renormalized due to the correlation and polaron effects.
Nd3+ induced twofold continuous spin reorientation transition and magnetization along the b-axis in a Dy0.9Nd0.1FeO3 single crystal
CrystEngComm
An intriguing hybrid magnetic configuration Γ4+3 with non-zero spontaneous magnetization along b-... more An intriguing hybrid magnetic configuration Γ4+3 with non-zero spontaneous magnetization along b-axis was found in DNFO91 single crystal. Contributions of R3+ were distinguished and the relative strength can be manipulated with magnetic field.
Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroi... more Detailed investigation of the incommensurate magnetic ordering in a single crystal of multiferroic NdMn2O5 has been performed using both non-polarized and polarized neutron diffraction techniques. Below TN ≈ 30.5 K magnetic Bragg reflections corresponding to the nonchiral type magnetic structure with propagation vector k1 = (0.5 0 kz1) occurs. Below about 27 K a new distorted magnetic modulation with a similar vector kz2 occurs, which is attributed to the magnetization of the Nd 3+ ions by the Mn-sub-lattice. Strong temperature hysteresis in the occurrence of the incommensurate magnetic phases in NdMn2O5 was observed depending on the cooling or heating history of the sample. Below about 20 K the magnetic structure became of a chiral type. From spherical neutron polarimetry measurements, the resulting low-temperature magnetic structure kz3 was approximated by the general elliptic helix. The parameters of the magnetic helix-like ellipticity and helical plane orientation in regard to the crystal structure were determined. A reorientation of the helix occurs at an intermediate temperature between 4 K and 18 K. A difference between the population of right-and left-handed chiral domains of about 0.2 was observed in the as-grown crystal when cooling without an external electric field. The magnetic chiral ratio can be changed by the application of an external electric field of a few kV/cm, revealing strong magnetoelectric coupling. A linear dependence of the magnetic chirality on the applied electric field in NdMn2O5 was found. The results are discussed within the frame of the antisymmetric super-exchange model for Dzyaloshinsky-Moria interaction. I.
[Ways to decrease the number of diagnostic errors and to improve the treatment results in acute appendicitis]
Vestnik khirurgii imeni I. I. Grekova, 1979
The investigation of 2114 patients admitted for acute appendicitis has shown that after an examin... more The investigation of 2114 patients admitted for acute appendicitis has shown that after an examination by the surgeon and the blood and urine tests the diagnosis of acute appendicitis was rejected in 922 patients (43%). Out of 1192 patients admitted to the hospital with the diagnosis of acute appendicitis 183 patients (15,4%) did not confirm the diagnosis of acute appendicitis after additional examination and observation of the patients.
... Louis Nel, Centre National de la Recherche Scientifique, 166X, 38042 Grenoble CEDEX, France I... more ... Louis Nel, Centre National de la Recherche Scientifique, 166X, 38042 Grenoble CEDEX, France IM Vitebsky Institut for Single Crystals, Ukranian Academy of Sciences, 310141 Kharkov, Ukraine A. Deville and B ... 9K. A. Kubat-Martin, Z. Fisk, and RR Ryan, Acta Crystal-logr. ...
Nuclear quadrupole resonance of barium in BaBiO3 and BaPbO3
Physical Review B, 2001
ABSTRACT The nuclear quadrupole resonance (NQR) on Ba nuclei was studied in four samples of BaBiO... more ABSTRACT The nuclear quadrupole resonance (NQR) on Ba nuclei was studied in four samples of BaBiO3 prepared in different ways and, in addition, in BaPbO3. The spectrum of 137Ba at T=4.2 K consists of a relatively broad line centered near 18 MHz for all BaBiO3 samples and near 13 MHz for BaPbO3. The integrated intensity of the 137Ba resonance in the ceramic sample of BaBiO3 synthesized at 800°C is approximately twice as large as that in ceramic samples and a single crystal prepared at 930–1080°C. The decrease of the NQR signal can be attributed to the partial disordering of charge-disproportionated Bi ions on the two inequivalent sites. The broadening of the resonance indicates that local distortions of the crystal structure exist in both compounds. The point-charge model was used to analyze the electric-field gradient on the Ba sites.
With the use of X-ray excited polar core-level and valence-band photoelectron-diffraction pattern... more With the use of X-ray excited polar core-level and valence-band photoelectron-diffraction patterns (XPED) and corresi~)ndmg energy distribution curves from TiO2(l10) (ruffle) along various azimuths in the surface plane, projected partial densities-of-states of the constituents in the valence band have been extracted. The results obtained from this angle-resolved method do not depend on the electron exit angle and seem to be a good measure for state densities of the bulk. A comparison with electronic structurt calculations is given.
Neutron diffraction studies of HoFeO3 single crystal were performed under external magnetic field... more Neutron diffraction studies of HoFeO3 single crystal were performed under external magnetic fields. The interplay between the external magnetic field, Dzyaloshinsky-Moria antisymmetric exchange and isotropic exchange interactions between Fe and Ho sublattice and inside Fe sublattice provides a rich phase diagram. As the result of the balance of exchange interactions inside crystal and external magnetic field we found 8 different magnetic phases, produced or suppressed by the field.
Neutron spectroscopy of 4f collective magnetic excitations in R 2 − x Ce x CuO 4 (R=Nd,Pr)
Physical Review B, 1997
We have studied the wave-vector dependence of the magnetic excitation spectrum of Nd in Nd 2-x Ce... more We have studied the wave-vector dependence of the magnetic excitation spectrum of Nd in Nd 2-x Ce x CuO 4 n (x= 0, 0.13) and of Pr in Pr 1.86 Ce 0.14 CuO 4 by inelastic neutron-scattering experiments on single crystals. The results are analyzed with the help of model ...
Raman study of crystal-field excitations in Pr2CuO4
Physical Review B, 1997
Raman measurements in a Pr2CuO4 single crystal show structures related to nine crystal-field (CF)... more Raman measurements in a Pr2CuO4 single crystal show structures related to nine crystal-field (CF) excitations. They correspond to transitions within the 3H4, 3H5, and 3H6 multiplets of Pr3+ ions in C4v site symmetry. Satellites to these CF excitations are also observed and associated with the presence of an inequivalent Pr3+ site of lower symmetry. A set of CF parameters which
Magnetic field switching of ferroelectricity in spiral magnet CuCrO2
ABSTRACT MARCH MEETING ABSTRACT: The triangular lattice antiferromagnet CuCrO2 show ferroelectric... more ABSTRACT MARCH MEETING ABSTRACT: The triangular lattice antiferromagnet CuCrO2 show ferroelectricity induced by a proper-screw spiral magnetic structure, where spins in form 120^o angles with neighboring spins due to frustration. CuCrO2 is thought to be a rare example of the Arima mechanism for multiferroic behavior. In addition, it has been shown that the magnetoelectric coupling can be tuned by both an electric and a magnetic field along ab-plane. We test a prediction for the magnetic field-evolution of the physical properties of CuCrO2 via magnetization and electric polarization measurements up to 65 T. We explore the complicated H-T phase diagram along different crystalline directions. In zero field, a spontaneous electric polarization in CuCrO2 is coupled to antiferromagnetic ordering below 24 K without an accompanying structural phase transition. In high fields, we observe electric polarization flops for magnetic fields applied along both the ab-plane and the c-axis, although at different magnetic fields than predicted. By contrast no noticeable anomaly is detected in magnetization isotherms, which are linear in fields up to 65 T. The electric polarization reversal is highly sensitive to the external magnetic field for both the ab-plane and c-axis due to a 3-dimensional proper-screw structure. We find that additional interactions may be necessary to explain our observed results.
The magnetization, resistivity and magnetoresistance (MR) of single crystals of GdBaCo 2 O 5.5 an... more The magnetization, resistivity and magnetoresistance (MR) of single crystals of GdBaCo 2 O 5.5 and EuBaCo 2 O 5.5 are measured over a wide range of dc magnetic fields (up to 30 T) and temperature. In LnBaCo 2 O 5.5 (Ln=Gd, Eu), the Co-ions are trivalent and can exist in three spin states, namely, the S=0 low spin state (LS), the S= 1 intermediate spin state (IS) and the S=2 high spin state (HS). We confirm that GdBaCo 2 O 5.5 and EuBaCo 2 O 5.5 have a metal-insulator transition accompanied by a spin-state transition at T MI ≈ 365 and 335 K, respectively. The data suggest an equal ratio of LS (S=0) and IS (S=1) Co 3+ ions below T MI , with no indication of additional spin state transitions. The low field magnetization shows a transition to a highly anisotropic ferromagnetic phase at 270 K, followed by another magnetic transition to an antiferromagnetic phase at a slightly lower temperature. The magnetization data are suggestive of weak correlations between the Gd-spins but no clear signature of ordering is seen for T > 2 K. Significant anisotropy between the a-b plane and c axis was observed in magnetic and magnetotransport properties for both compounds. For GdBaCo 2 O 5.5 , the resistivity and MR data imply a strong correlation between the spin-order and charge carriers. For EuBaCo 2 O 5.5 , the magnetic phase diagram is very similar to its Gd counterpart, but the low-T MR with current flow in the ab plane is positive rather than negative as for Gd. The magnitude and the hysteresis of the MR for EuBaCo 2 O 5.5 decrease with increasing temperature, and at higher T the MR changes sign and becomes negative. The difference
Observation of Cu 2 + spin resonance in Gd 2 CuO 4
Physical Review B, 1995
We report on the detection of Cu2+ spin resonance in a compound belonging to a family of electron... more We report on the detection of Cu2+ spin resonance in a compound belonging to a family of electron-doped high-temperature superconducting materials with general formula R2-xCexCuO4. Experiments were carried out on single Gd2CuO4 crystals at low temperatures using millimeter and far-infrared techniques combined with high magnetic fields. Three antiferromagnetic resonance branches are observed with the following frequency gaps at 2 K: omega1=0.8 cm-1, omega2=2.8 cm-1, Omega2=17 cm-1. The omega1 and omega2 frequencies correspond to the Gd magnetic subsystem. The characteristic field and temperature dependence of the Omega2 resonance allow us to identify it as the Cu spin resonance.
Competing Interactions in the $S$=3/2 Kagome Staircase Co$_{3}$V$_{2}$O$_{8}$: Evolution of the Commensurate and Incommensurate Phases in a Magnetic Field
Core-level photoemission and x-ray absorption study of Na-covered and oxygen-deficient Ba 0.6 K 0.4 BiO 3 − y single crystals
Physical Review B, 1998
ABSTRACT To study the effects of doping in Ba0.6K0.4BiO3, core-level and valence-band photoemissi... more ABSTRACT To study the effects of doping in Ba0.6K0.4BiO3, core-level and valence-band photoemission results are presented for a single crystal with various Na coverages and for an oxygen-deficient sample. It was found that the valence band and the Ba 4d, Ba 5p, Bi 5d, and O 1s core levels were shifted to higher binding energies with increasing Na coverage, consistent with an increase in band filling, whereas for K 2p, the shift was negligible. The valence band broadens as Na is deposited but the intensity at the Fermi level stays constant, in line with the n-type nature of the charge carriers in Ba1-xKxBiO3. The prepeak intensity in the O K edge absorption spectrum as well as the Bi 4f asymmetry were found to be lower for oxygen-deficient Ba0.6K0.4BiO3-y than for the stoichiometric samples, indicating the importance of oxygen content for metallic Ba0.6K0.4BiO3. The asymmetry of the Bi 4f increased with Na deposition, suggesting the growth of a high binding energy component with reduced valency, whereas the Ba 4d, Ba 5p, and K 2p became narrower, consistent with a decrease of the surface-core-level shifts.
ABSTRACT We have made neutron-diffraction, magnetization, and antiferromagnetic-resonance investi... more ABSTRACT We have made neutron-diffraction, magnetization, and antiferromagnetic-resonance investigations of Gd2CuO4 single crystals. Neutron-diffraction experiments on 158enriched Gd2CuO4 single crystals show that the gadolinium atoms order antiferromagnetically at TN=6.4 K with the propagation vector k=(0,0,0). The two Gd atoms of the primitive unit cell related by the center of symmetry are oppositely oriented. The antiferromagnetic-resonance spectra indicate that Gd2CuO4 belongs to the class of ‘‘easy-plane’’ antiferromagnets and show the presence of a second-order reorientation phase transition at Hc=0.88 T (H∥[100], T=1.8 K). The magnetization measurements confirm the presence of this reorientation transition and also show a complete ferromagnetic alignment of Gd moments at H=11 T and T=1.5 K.
Orbital fluctuating state in ferromagnetic insulating LaMnO3+δ (0.085⩽δ⩽0.125) studied using Raman spectroscopy
Physical Review B, 2006
K.-Y. Choi,1 Yu. G. Pashkevich,2 VP Gnezdilov,3 G. Güntherodt,4 AV Yeremenko,3 DA Nabok,2 VI Kame... more K.-Y. Choi,1 Yu. G. Pashkevich,2 VP Gnezdilov,3 G. Güntherodt,4 AV Yeremenko,3 DA Nabok,2 VI Kamenev,2 SN Barilo,5 SV Shiryaev,5 AG Soldatov,5 and P. Lemmens6 1Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan 2A. ...
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