Zouhair Sefrioui - Academia.edu (original) (raw)

Papers by Zouhair Sefrioui

Research paper thumbnail of Magnetization reversal in complex oxide magnetic tunnel junctions

We have investigated the magnetization reversal of La0.7Ca0.3MnO3 (LCMO)/PrBa2Cu3O7(PBCO)/LCMO ma... more We have investigated the magnetization reversal of La0.7Ca0.3MnO3 (LCMO)/PrBa2Cu3O7(PBCO)/LCMO magnetic tunnels junctions with Polarized Neutron Reflectivity (PNR) in order to better understand the observed tunneling magnetoresistance (TMR) behavior. The TMR initially increases with decreasing temperature but then reaches a maximum at a relatively high temperature (60 K) and decreases when the temperature is further decreased. PNR measurements reveal differences in

Research paper thumbnail of Magnetic Coupling in La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub>/YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub>/La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub> Trilayers

Defect and Diffusion Forum, 2009

We report on the interplay between ferromagnetism and superconductivity in trilayers La{sub 0.7}C... more We report on the interplay between ferromagnetism and superconductivity in trilayers La{sub 0.7}Ca{sub 0.3}MnO/YBaCuO/La{sub 0.7}Ca{sub 0.3}MnO made of half metallic manganite and high temperature superconductor cuprate. Samples with a fully oxygenated cuprate show a magnetic field interval where the magnetizations of the manganite are aligned antiparallel. A considerable magnetoresistance accompanies the switching between magnetization configurations (parallel vs. antiparallel) of the

Research paper thumbnail of Enhanced ionic conductivity in oxide heterostructures

Fuel cells are electrochemical devices used to generate energy out of hydrogen. In a fuel cell, t... more Fuel cells are electrochemical devices used to generate energy out of hydrogen. In a fuel cell, two conducting electrodes are separated by an electrolyte that is permeable to ions (either hydrogen or oxygen, depending on the fuel-cell category) but not to electrons. An electrode catalytic process yields the ionic species, which are transported through the electrolyte, while electrons blocked by

Research paper thumbnail of Non monotonic depression of the critical temperature in La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 trilayers

We have grown LCMO/YBCO/LCMO trilayers by high oxygen pressure sputtering technique on (100) SrTi... more We have grown LCMO/YBCO/LCMO trilayers by high oxygen pressure sputtering technique on (100) SrTiO3. The thickness of the YBCO layer was fixed in 12 unit cells and the thickness of the magnetic layers was varied betwen 3 and 150 unit cells. A structural study using x_ray refinement and transmission electron microscopy shows sharp interfaces with a high degree of strctural

Research paper thumbnail of Colossal ionic conductivity at ZrO2:Y2O3 /SrTiO3 interfaces

We describe the strong enhancement of the conductivity occurring at the interfaces of superlattic... more We describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating 10 nm strontium titanate and 1 nm yttria stabilized zirconia ^[1]layers. Conductivity is found to be as high as 0.014 S/cm at 357 K, with a substantial decrease of the activation energy for the dc ionic conductivity from 1.1 eV down to 0.64

Research paper thumbnail of Long Range Interaction Between Magnetism and Superconductivity in La0.3Ca0.7 MnO3/ YBa2Cu3O7 Superlattices

We have grown epitaxial La0.3Ca0.7 MnO3(LCMO)/ YBa2Cu3O7 (YBCO) superlattices by high oxygen pres... more We have grown epitaxial La0.3Ca0.7 MnO3(LCMO)/ YBa2Cu3O7 (YBCO) superlattices by high oxygen pressure sputtering technique on (100) SrTiO3 changing the thickness of the individual layers between 1 and 15 nm. A structural study using x-ray refinement and transmission electron microscopy shows sharp interfaces with a high degree of structural perfection [1]. Magnetization (SQUID) and transport measurements show the coexistence of

Research paper thumbnail of Block by Block Growth of Ultrathin YBa2Cu3O 7-x in YBa2Cu3O 7-x/PrBa2Cu3O7 Superlattices

High quality [YBa2Cu3O 7-x n u.c. /PrBa2Cu3O7 5 u.c.] 1000Å superlattices with noninteger YBa2Cu3... more High quality [YBa2Cu3O 7-x n u.c. /PrBa2Cu3O7 5 u.c.] 1000Å superlattices with noninteger YBa2Cu3O7-x layer thickness have been grown to investigate the growth mechanism of YBCO. We unambiguously show the block by block deposition as opposed to atomic layer by layer growth modes [1,2]. Samples were grown on SrTiO3 substrates by high oxygen pressure sputtering. Interfacial morphology has been characterized by x-ray diffraction (XRD) and energy filtered transmission electron microscopy (EFTEM). X ray refinement shows no interdiffusion, negligible interfacial roughness and significant epitaxial strain for YBCO layers, with thickness below 3 unit cells [3, 4]. X ray analysis shows that in superlattices with non integer YBCO layers, the superlattice modulation length does not commensurate with the underlying lattice [5]. EFTEM analysis shows the presence of interface steps one unit cell high, distributed in such a way that the interface plane composition changes coherently with increasin...

Research paper thumbnail of Direct correlation between Tc and CuO2 bilayer spacing in YBa2Cu3O7-x

Physical Review B, 2002

We report the effects of epitaxial strain and deoxygenation on high quality [YBa 2 Cu 3 O 7−x (YB... more We report the effects of epitaxial strain and deoxygenation on high quality [YBa 2 Cu 3 O 7−x (YBCO) N / PrBa 2 Cu 3 O 7 (PBCO) 5 ] 1000Å superlattices, with 1 <N<12 unit cells. High spatial resolution electron energy loss spectroscopy (EELS) shows that strained, fully oxygenated YBCO layers are underdoped.

Research paper thumbnail of Epitaxial mismatch strain in YBa2Cu3O7-δ/PrBa2Cu 3O7 superlattices

The effects of epitaxial strain in ultrathin YBa2Cu3O7-delta layers have been investigated by x-r... more The effects of epitaxial strain in ultrathin YBa2Cu3O7-delta layers have been investigated by x-ray diffraction and transmission electron microscopy. The samples used were high quality [YBa2Cu3O7-delta (YBCO)N/PrBa2Cu3O7 (PBCO)M]1000 Å superlattices, grown by high oxygen pressure sputtering, with N ranging between 1 and 12 unit cells and M=5 unit cells. Superlattice structure is refined by fitting x-ray spectra to a structural

Research paper thumbnail of Electron-electron interaction and weak localization effects in badly metallic SrRuO3

Physical Review B, 2001

We report on the effect of light ion irradiation on the low-temperature electrical resistivity of... more We report on the effect of light ion irradiation on the low-temperature electrical resistivity of ferromagnetic SrRuO 3 thin films. Fresh samples displayed a ferromagnetic transition at T c ϳ160 K, good metallic behavior "(300 K)ϳ400 ⍀ cm, d/dTϾ0… at room temperature, and the low-temperature upturn in the electrical resistivity commonly found in SrRuO 3 . Badly metallic films, displaying high values of the electrical resistivity "O(1000 ⍀ cm)… and incipient nonmetallic behavior (d/dTϽ0) at low temperature, were obtained by He ϩ irradiation. For high enough irradiation doses, these samples did not show magnetic order down to the base temperature of our experiments. The temperature dependence of the electrical conductivity of virgin and irradiated samples is discussed in terms of a weak localization contribution plus a large electron-electron interaction term. The magnitude of the e Ϫ -e Ϫ contribution reflects the enhancement of strong electron correlations in SrRuO 3 due to disorder.

Research paper thumbnail of Ferromagnetic/superconducting proximity effect in La0.7Ca0.3MnO3/YBa2Cu3O7-δ superlattices

Physical Review B, 2003

We study the interplay between magnetism and superconductivity in high quality YBa 2 Cu 3 O 7 (YB... more We study the interplay between magnetism and superconductivity in high quality YBa 2 Cu 3 O 7 (YBCO) / La 0.7 Ca 0.3 MnO 3 (LCMO) superlattices. We find evidence for the YBCO superconductivity depression in presence of the LCMO layers. We show that due to its short coherence length superconductivity survives in the YBCO down to much smaller thickness in presence of the magnetic layer than in low Tc superconductors. We also find that for a fixed thickness of the superconducting layer, superconductivity is depressed over a thickness interval of the magnetic layer in the 100 nm range. This is a much longer length scale than that predicted by the theory of ferromagnetic/superconducting proximity effect.

Research paper thumbnail of Oscillatory behavior of the magnetoresistance of F/S/F trilayers

We have measured magnetoresistance of trilayers made of highly spin polarized La0.7Ca0.3MnO3 ferr... more We have measured magnetoresistance of trilayers made of highly spin polarized La0.7Ca0.3MnO3 ferromagnets and high-Tc superconducting YBa2Cu3O7-delta with the current in plane (CIP) geometry. Large magnetoresistance peaks occur for antiferromagnetic (AF) alignment of the manganite layers, much resembling the GMR in metallic superlattices, and probably resulting of enhanced interface scattering in the AF configuration. We show RKKY-type oscillations in the

Research paper thumbnail of Effects of epitaxial strain on the growth mechanism in YBa2Cu3O7-x thin films in YBa2Cu3O7-x/PrBa2Cu3O7 superlattices

Physical Review B, 2002

We report on the growth mechanism of YBa 2 Cu 3 O 7−x . Our study is based on the analysis of ult... more We report on the growth mechanism of YBa 2 Cu 3 O 7−x . Our study is based on the analysis of ultrathin, YBa 2 Cu 3 O 7−x layers in c-axis oriented YBa 2 Cu 3 O 7−x / PrBa 2 Cu 3 O 7 superlattices. We have found that the release of epitaxial strain in very thin YBCO layers triggers a change in the dimensionality of the growth mode. Ultrathin, epitaxially strained, YBCO layers with thickness below 3 unit cells grow in a block by block two dimensional mode coherent over large lateral distances. Meanwhile, when thickness increases, and the strain relaxes, layer growth turns into three dimensional, resulting in rougher layers and interfaces.

Research paper thumbnail of Modified doping at cuprate / lanthanum manganite interfaces

Oxide heterostructures allow combining materials with similar structure but with very different g... more Oxide heterostructures allow combining materials with similar structure but with very different ground states, which may compete at the interface to yield novel behaviors and functionalities. We explore the YBa2Cu3O7 (YBCO) / La1-xCaxMnO3 (LCMO) interface in thin film heterostructures. For x=0.3 the manganite is ferromagnetic which causes a strong depression of the superconductivity at the YBCO side. There is also a depression of the ferromagnetic moment at the interface suggesting electron transfer from the manganite into the YBCO. This is confirmed from superlattices alternating YBCO and LaMnO3 (LMO), an A- type AF insulator. While for thin LMO layers (< 6 unit cells) there is little effect on YBCO superconductivity, thicker LMO layers result in reduced Tc values and induced ferromagnetism at the interface, thus providing a firm indication of charge transfer. The occurrence of charge transfer over length scales much longer than the Thomas Fermi screening length (1 nm) is a nove...

Research paper thumbnail of Magnetic depth profiles of complex oxide F/S/F trilayers

Bulletin of the American …, 2008

The origin of the large magnetoresitance in epitaxial F/S/F trilayers composed of highly spin pol... more The origin of the large magnetoresitance in epitaxial F/S/F trilayers composed of highly spin polarized ferromagnetic La $ _ {0.7} $ Ca $ _ {0.3} $ MnO $ _ {3} $ and high-T $ _ {c} $ superconducting YBa $ _ {2} $ Cu $ _ {3} $ O $ _ {7-\ delta} $(YBCO) is investigated by ...

Research paper thumbnail of Nanoscale analysis of YBa2Cu3O7−x/La0.67Ca0.33MnO3 interfaces

Solid-State Electronics, 2003

The structure of interfaces in superconducting/ferromagnetic YBa2Cu3O7− x/La0. 67Ca0. 33MnO3 supe... more The structure of interfaces in superconducting/ferromagnetic YBa2Cu3O7− x/La0. 67Ca0. 33MnO3 superlattices has been analyzed by scanning transmission electron microscopy and high spatial resolution electron energy loss spectroscopy. Individual layers are flat ...

Research paper thumbnail of Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures

Science, 2008

8 mol% (Y 2 O 3 ) x (ZrO 2 ) 1-x (YSZ) and SrTiO 3 (STO) layers were grown on STO (100) substrate... more 8 mol% (Y 2 O 3 ) x (ZrO 2 ) 1-x (YSZ) and SrTiO 3 (STO) layers were grown on STO (100) substrates in a high pressure (3 mbar) pure oxygen RF sputtering system. High pressure and high substrate temperature (900 ºC) ensures a slow (1 nm/min) and highly thermalized growth of complex oxides providing excellent epitaxial properties (S1, S2). STO / YSZ / STO trilayers were grown keeping the STO thickness constant at 10 nm or 25 unit cells (u. c.), and systematically varying the YSZ thickness in the following steps: 1, 5, 30, and 62 nm (2, 10, 60, 120 u. c. respectively). Superlattices were also fabricated, with several YSZ thicknesses, and 10 nm of STO, repeated different times (between 2 and 20).

Research paper thumbnail of Response to Comment on "Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures

Science, 2009

Guo suggests that the reported ionic conductivity of ZrO2:Y2O3/SrTiO3 heterostructures might be d... more Guo suggests that the reported ionic conductivity of ZrO2:Y2O3/SrTiO3 heterostructures might be due to the electronic conductivity from the SrTiO3. We point out shortcomings in his reasoning and underscore that our results show that any electronic contribution to the conductance is at least three orders of magnitude lower than the ionic contribution determined by ac methods.

Research paper thumbnail of Giant Magnetoresistance in Ferromagnet/Superconductor Superlattices

Physical Review Letters, 2005

We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7C... more We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7Ca0.3MnO3 and high-Tc superconducting YBa2Cu3O7. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the YBa2Cu3O7 layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.

Research paper thumbnail of Intracell Changes in Epitaxially Strained YBa2Cu3O7-x Ultrathin Layers in YBa2Cu3O7-x/PrBa2Cu3O7 Superlattices

Physical Review Letters, 1999

The structure of high quality [YBCO N /PBCO M ] 1000 Å superlattices, with N ranging between 1 an... more The structure of high quality [YBCO N /PBCO M ] 1000 Å superlattices, with N ranging between 1 and 12 unit cells and M = 5 unit cells, grown by high oxygen pressure sputtering, is analyzed. Intracell atomic structure of the layers along the c axis and disorder at ...

Research paper thumbnail of Magnetization reversal in complex oxide magnetic tunnel junctions

We have investigated the magnetization reversal of La0.7Ca0.3MnO3 (LCMO)/PrBa2Cu3O7(PBCO)/LCMO ma... more We have investigated the magnetization reversal of La0.7Ca0.3MnO3 (LCMO)/PrBa2Cu3O7(PBCO)/LCMO magnetic tunnels junctions with Polarized Neutron Reflectivity (PNR) in order to better understand the observed tunneling magnetoresistance (TMR) behavior. The TMR initially increases with decreasing temperature but then reaches a maximum at a relatively high temperature (60 K) and decreases when the temperature is further decreased. PNR measurements reveal differences in

Research paper thumbnail of Magnetic Coupling in La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub>/YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub>/La<sub>0.7</sub>Ca<sub>0.3</sub>MnO<sub>3</sub> Trilayers

Defect and Diffusion Forum, 2009

We report on the interplay between ferromagnetism and superconductivity in trilayers La{sub 0.7}C... more We report on the interplay between ferromagnetism and superconductivity in trilayers La{sub 0.7}Ca{sub 0.3}MnO/YBaCuO/La{sub 0.7}Ca{sub 0.3}MnO made of half metallic manganite and high temperature superconductor cuprate. Samples with a fully oxygenated cuprate show a magnetic field interval where the magnetizations of the manganite are aligned antiparallel. A considerable magnetoresistance accompanies the switching between magnetization configurations (parallel vs. antiparallel) of the

Research paper thumbnail of Enhanced ionic conductivity in oxide heterostructures

Fuel cells are electrochemical devices used to generate energy out of hydrogen. In a fuel cell, t... more Fuel cells are electrochemical devices used to generate energy out of hydrogen. In a fuel cell, two conducting electrodes are separated by an electrolyte that is permeable to ions (either hydrogen or oxygen, depending on the fuel-cell category) but not to electrons. An electrode catalytic process yields the ionic species, which are transported through the electrolyte, while electrons blocked by

Research paper thumbnail of Non monotonic depression of the critical temperature in La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 trilayers

We have grown LCMO/YBCO/LCMO trilayers by high oxygen pressure sputtering technique on (100) SrTi... more We have grown LCMO/YBCO/LCMO trilayers by high oxygen pressure sputtering technique on (100) SrTiO3. The thickness of the YBCO layer was fixed in 12 unit cells and the thickness of the magnetic layers was varied betwen 3 and 150 unit cells. A structural study using x_ray refinement and transmission electron microscopy shows sharp interfaces with a high degree of strctural

Research paper thumbnail of Colossal ionic conductivity at ZrO2:Y2O3 /SrTiO3 interfaces

We describe the strong enhancement of the conductivity occurring at the interfaces of superlattic... more We describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating 10 nm strontium titanate and 1 nm yttria stabilized zirconia ^[1]layers. Conductivity is found to be as high as 0.014 S/cm at 357 K, with a substantial decrease of the activation energy for the dc ionic conductivity from 1.1 eV down to 0.64

Research paper thumbnail of Long Range Interaction Between Magnetism and Superconductivity in La0.3Ca0.7 MnO3/ YBa2Cu3O7 Superlattices

We have grown epitaxial La0.3Ca0.7 MnO3(LCMO)/ YBa2Cu3O7 (YBCO) superlattices by high oxygen pres... more We have grown epitaxial La0.3Ca0.7 MnO3(LCMO)/ YBa2Cu3O7 (YBCO) superlattices by high oxygen pressure sputtering technique on (100) SrTiO3 changing the thickness of the individual layers between 1 and 15 nm. A structural study using x-ray refinement and transmission electron microscopy shows sharp interfaces with a high degree of structural perfection [1]. Magnetization (SQUID) and transport measurements show the coexistence of

Research paper thumbnail of Block by Block Growth of Ultrathin YBa2Cu3O 7-x in YBa2Cu3O 7-x/PrBa2Cu3O7 Superlattices

High quality [YBa2Cu3O 7-x n u.c. /PrBa2Cu3O7 5 u.c.] 1000Å superlattices with noninteger YBa2Cu3... more High quality [YBa2Cu3O 7-x n u.c. /PrBa2Cu3O7 5 u.c.] 1000Å superlattices with noninteger YBa2Cu3O7-x layer thickness have been grown to investigate the growth mechanism of YBCO. We unambiguously show the block by block deposition as opposed to atomic layer by layer growth modes [1,2]. Samples were grown on SrTiO3 substrates by high oxygen pressure sputtering. Interfacial morphology has been characterized by x-ray diffraction (XRD) and energy filtered transmission electron microscopy (EFTEM). X ray refinement shows no interdiffusion, negligible interfacial roughness and significant epitaxial strain for YBCO layers, with thickness below 3 unit cells [3, 4]. X ray analysis shows that in superlattices with non integer YBCO layers, the superlattice modulation length does not commensurate with the underlying lattice [5]. EFTEM analysis shows the presence of interface steps one unit cell high, distributed in such a way that the interface plane composition changes coherently with increasin...

Research paper thumbnail of Direct correlation between Tc and CuO2 bilayer spacing in YBa2Cu3O7-x

Physical Review B, 2002

We report the effects of epitaxial strain and deoxygenation on high quality [YBa 2 Cu 3 O 7−x (YB... more We report the effects of epitaxial strain and deoxygenation on high quality [YBa 2 Cu 3 O 7−x (YBCO) N / PrBa 2 Cu 3 O 7 (PBCO) 5 ] 1000Å superlattices, with 1 <N<12 unit cells. High spatial resolution electron energy loss spectroscopy (EELS) shows that strained, fully oxygenated YBCO layers are underdoped.

Research paper thumbnail of Epitaxial mismatch strain in YBa2Cu3O7-δ/PrBa2Cu 3O7 superlattices

The effects of epitaxial strain in ultrathin YBa2Cu3O7-delta layers have been investigated by x-r... more The effects of epitaxial strain in ultrathin YBa2Cu3O7-delta layers have been investigated by x-ray diffraction and transmission electron microscopy. The samples used were high quality [YBa2Cu3O7-delta (YBCO)N/PrBa2Cu3O7 (PBCO)M]1000 Å superlattices, grown by high oxygen pressure sputtering, with N ranging between 1 and 12 unit cells and M=5 unit cells. Superlattice structure is refined by fitting x-ray spectra to a structural

Research paper thumbnail of Electron-electron interaction and weak localization effects in badly metallic SrRuO3

Physical Review B, 2001

We report on the effect of light ion irradiation on the low-temperature electrical resistivity of... more We report on the effect of light ion irradiation on the low-temperature electrical resistivity of ferromagnetic SrRuO 3 thin films. Fresh samples displayed a ferromagnetic transition at T c ϳ160 K, good metallic behavior "(300 K)ϳ400 ⍀ cm, d/dTϾ0… at room temperature, and the low-temperature upturn in the electrical resistivity commonly found in SrRuO 3 . Badly metallic films, displaying high values of the electrical resistivity "O(1000 ⍀ cm)… and incipient nonmetallic behavior (d/dTϽ0) at low temperature, were obtained by He ϩ irradiation. For high enough irradiation doses, these samples did not show magnetic order down to the base temperature of our experiments. The temperature dependence of the electrical conductivity of virgin and irradiated samples is discussed in terms of a weak localization contribution plus a large electron-electron interaction term. The magnitude of the e Ϫ -e Ϫ contribution reflects the enhancement of strong electron correlations in SrRuO 3 due to disorder.

Research paper thumbnail of Ferromagnetic/superconducting proximity effect in La0.7Ca0.3MnO3/YBa2Cu3O7-δ superlattices

Physical Review B, 2003

We study the interplay between magnetism and superconductivity in high quality YBa 2 Cu 3 O 7 (YB... more We study the interplay between magnetism and superconductivity in high quality YBa 2 Cu 3 O 7 (YBCO) / La 0.7 Ca 0.3 MnO 3 (LCMO) superlattices. We find evidence for the YBCO superconductivity depression in presence of the LCMO layers. We show that due to its short coherence length superconductivity survives in the YBCO down to much smaller thickness in presence of the magnetic layer than in low Tc superconductors. We also find that for a fixed thickness of the superconducting layer, superconductivity is depressed over a thickness interval of the magnetic layer in the 100 nm range. This is a much longer length scale than that predicted by the theory of ferromagnetic/superconducting proximity effect.

Research paper thumbnail of Oscillatory behavior of the magnetoresistance of F/S/F trilayers

We have measured magnetoresistance of trilayers made of highly spin polarized La0.7Ca0.3MnO3 ferr... more We have measured magnetoresistance of trilayers made of highly spin polarized La0.7Ca0.3MnO3 ferromagnets and high-Tc superconducting YBa2Cu3O7-delta with the current in plane (CIP) geometry. Large magnetoresistance peaks occur for antiferromagnetic (AF) alignment of the manganite layers, much resembling the GMR in metallic superlattices, and probably resulting of enhanced interface scattering in the AF configuration. We show RKKY-type oscillations in the

Research paper thumbnail of Effects of epitaxial strain on the growth mechanism in YBa2Cu3O7-x thin films in YBa2Cu3O7-x/PrBa2Cu3O7 superlattices

Physical Review B, 2002

We report on the growth mechanism of YBa 2 Cu 3 O 7−x . Our study is based on the analysis of ult... more We report on the growth mechanism of YBa 2 Cu 3 O 7−x . Our study is based on the analysis of ultrathin, YBa 2 Cu 3 O 7−x layers in c-axis oriented YBa 2 Cu 3 O 7−x / PrBa 2 Cu 3 O 7 superlattices. We have found that the release of epitaxial strain in very thin YBCO layers triggers a change in the dimensionality of the growth mode. Ultrathin, epitaxially strained, YBCO layers with thickness below 3 unit cells grow in a block by block two dimensional mode coherent over large lateral distances. Meanwhile, when thickness increases, and the strain relaxes, layer growth turns into three dimensional, resulting in rougher layers and interfaces.

Research paper thumbnail of Modified doping at cuprate / lanthanum manganite interfaces

Oxide heterostructures allow combining materials with similar structure but with very different g... more Oxide heterostructures allow combining materials with similar structure but with very different ground states, which may compete at the interface to yield novel behaviors and functionalities. We explore the YBa2Cu3O7 (YBCO) / La1-xCaxMnO3 (LCMO) interface in thin film heterostructures. For x=0.3 the manganite is ferromagnetic which causes a strong depression of the superconductivity at the YBCO side. There is also a depression of the ferromagnetic moment at the interface suggesting electron transfer from the manganite into the YBCO. This is confirmed from superlattices alternating YBCO and LaMnO3 (LMO), an A- type AF insulator. While for thin LMO layers (< 6 unit cells) there is little effect on YBCO superconductivity, thicker LMO layers result in reduced Tc values and induced ferromagnetism at the interface, thus providing a firm indication of charge transfer. The occurrence of charge transfer over length scales much longer than the Thomas Fermi screening length (1 nm) is a nove...

Research paper thumbnail of Magnetic depth profiles of complex oxide F/S/F trilayers

Bulletin of the American …, 2008

The origin of the large magnetoresitance in epitaxial F/S/F trilayers composed of highly spin pol... more The origin of the large magnetoresitance in epitaxial F/S/F trilayers composed of highly spin polarized ferromagnetic La $ _ {0.7} $ Ca $ _ {0.3} $ MnO $ _ {3} $ and high-T $ _ {c} $ superconducting YBa $ _ {2} $ Cu $ _ {3} $ O $ _ {7-\ delta} $(YBCO) is investigated by ...

Research paper thumbnail of Nanoscale analysis of YBa2Cu3O7−x/La0.67Ca0.33MnO3 interfaces

Solid-State Electronics, 2003

The structure of interfaces in superconducting/ferromagnetic YBa2Cu3O7− x/La0. 67Ca0. 33MnO3 supe... more The structure of interfaces in superconducting/ferromagnetic YBa2Cu3O7− x/La0. 67Ca0. 33MnO3 superlattices has been analyzed by scanning transmission electron microscopy and high spatial resolution electron energy loss spectroscopy. Individual layers are flat ...

Research paper thumbnail of Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures

Science, 2008

8 mol% (Y 2 O 3 ) x (ZrO 2 ) 1-x (YSZ) and SrTiO 3 (STO) layers were grown on STO (100) substrate... more 8 mol% (Y 2 O 3 ) x (ZrO 2 ) 1-x (YSZ) and SrTiO 3 (STO) layers were grown on STO (100) substrates in a high pressure (3 mbar) pure oxygen RF sputtering system. High pressure and high substrate temperature (900 ºC) ensures a slow (1 nm/min) and highly thermalized growth of complex oxides providing excellent epitaxial properties (S1, S2). STO / YSZ / STO trilayers were grown keeping the STO thickness constant at 10 nm or 25 unit cells (u. c.), and systematically varying the YSZ thickness in the following steps: 1, 5, 30, and 62 nm (2, 10, 60, 120 u. c. respectively). Superlattices were also fabricated, with several YSZ thicknesses, and 10 nm of STO, repeated different times (between 2 and 20).

Research paper thumbnail of Response to Comment on "Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO2:Y2O3/SrTiO3 Heterostructures

Science, 2009

Guo suggests that the reported ionic conductivity of ZrO2:Y2O3/SrTiO3 heterostructures might be d... more Guo suggests that the reported ionic conductivity of ZrO2:Y2O3/SrTiO3 heterostructures might be due to the electronic conductivity from the SrTiO3. We point out shortcomings in his reasoning and underscore that our results show that any electronic contribution to the conductance is at least three orders of magnitude lower than the ionic contribution determined by ac methods.

Research paper thumbnail of Giant Magnetoresistance in Ferromagnet/Superconductor Superlattices

Physical Review Letters, 2005

We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7C... more We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7Ca0.3MnO3 and high-Tc superconducting YBa2Cu3O7. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the YBa2Cu3O7 layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.

Research paper thumbnail of Intracell Changes in Epitaxially Strained YBa2Cu3O7-x Ultrathin Layers in YBa2Cu3O7-x/PrBa2Cu3O7 Superlattices

Physical Review Letters, 1999

The structure of high quality [YBCO N /PBCO M ] 1000 Å superlattices, with N ranging between 1 an... more The structure of high quality [YBCO N /PBCO M ] 1000 Å superlattices, with N ranging between 1 and 12 unit cells and M = 5 unit cells, grown by high oxygen pressure sputtering, is analyzed. Intracell atomic structure of the layers along the c axis and disorder at ...