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We demonstrate generation of time-resolved THz transients in a FeCo/graphene nanobilayer, excited by femtosecond optical laser pulses. The signal sign dependency on the experimental geometry and the external magnetic field allows assigning the mechanism of the THz radiation to the inverse spin Hall effect with a spin-to-charge current conversation parameter of the order of 0.001 nm.

We report on the generation of electromagnetic transients of picosecond duration from La-Sr-Mn-O/Au and La-Sr-Mn-O/lr nanobilayers, illuminated by femtosecond laser pulses in the presence of an external magnetic field. Fourier analysis revealed that the frequency content of these transients extended up 4 THz. The amplitude of THz transients followed the functional dependence of La-Sr-Mn-O magnetization on the magnetic field and was also tunable by varying the intensity of the optical pulses. We ascribe the observed emission of THz transients to the inverse spin Hall effect, earlier demonstrated in metallic ferromagnet/metal spintronic nanobilayers.

We have generated intense electromagnetic transients by femtosecond laser pulse illumination of ferromagnet/metal (F/M) nanobilayers, in the presence of an external magnetic field. Fourier analysis revealed that the frequency content of these transients extended up to ~5 THz. We have also observed that upon the increase of the magnetic field, the entire THz transient shifts towards earlier times by up to 110 fs. We ascribe this magnetically tunable onset-time shift to extra acceleration of photoelectrons induced due to the Lorenz force.

The magnetic anisotropy (MA) of Mo/Au/Co0.9Fe0.1/Au/MgO(0.7–3 nm)/Au/Co0.9Fe0.1/Au heterostructure has been investigated at room temperature as a function of MgO layer thickness (tMgO). Our studies show that while the MA of the top layer does not change its character upon variation of tMgO, the uniaxial out-of-plane MA of the bottom one undergoes a spin reorientation transition at tMgO of about 0.8 nm, switching to the regime where the coexistence of in- and out-of-plane magnetization alignments is observed. The magnitudes of the magnetic anisotropy constants have been determined from ferromagnetic resonance and dc-magnetometry measurements. The origin of MA evolution has been attributed to a presence of an interlayer exchange coupling (IEC) between Co0.9Fe0.1 layers through the thin MgO film.

A series of MgB2 samples doped with C, RE2O3 oxides (RE = Ce, Nd), and C and RE2O3oxides was prepared by the hot isostatic pressing method at high pressure: 1 GPa under argon gas. Based on X-ray diffraction and magnetization measurements it was found that the RE2O3 is not incorporated into MgB2. A secondary REB4 phase is present after the synthesis. No decrease in the critical temperature (Tc) is observed after the RE2O3 doping. The Tc of C and RE2O3 doped MgB2 is decreased by 3 K. The doping decreases the diamagnetic response in comparison to pure MgB2 phase. The highest critical current density (Jc) was 3.4 × 105 A/cm2 at 4.2 K and 0.5 T for the bulk material, and the irreversibility field for the Nd2O3 doped sample was located at high field at T = 30 K. The results indicate that inside grains of pinning centers increase Jc from 4.2 K to 25 K and decrease Jc at 30 K. On the other hand, pinning centers between grains (precipitate) increase Jc at 30 K and decrease Jc from 4.2 K to 25 K in the middle and high magnetic fields. Our research shows that carbon-encapsulated boron creates a point pinning centers.

We report on preparation and electrical characterization of the epitaxial BaTiO3 (BTO), BiFeO3 (BFO) thin films and BFO/BTO biand multilayers, grown on (001) SrTiO3 (STO) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) substrates. The ferroelectric properties were characterized using the electric force microscopy method to image and switch the electric domains. This fabrication process opens the routes towards wide study of magnetoelectric effect in complex oxide heterostructures.

We present magnetoresistance measurements on La 0.7 Sr 0.3 MnO 3 /YBCO/La 0.7 Sr 0.3 MnO 3 /YBCO (L1/Y1/L2/Y) heterostructure. The Ll/Y1/L2/Y spin valve shows large magnetoresistance peaks in coercive field at temperatures below the onset of the superconducting transition. The rotation in parallel magnetic field demonstrates a change of magnetoresistance; simultaneously the transition temperature to superconducting state T c0 ( H =450 Oe, β ) exhibits nonmonotonic dependence due to change of noncolinearity of magnetic moments of LSMO layers. Nonmonotonic change of the transition temperature as a function of angle is interpreted as a signature of generation of the triplet component superconducting phase in the Ll/Y1/L2/Y heterostructure.

Using combined magnetometry and ferromagnetic resonance studies, it is shown that introduction of a hydrocarbon cover layer leads to an increase of the contribution of the surface anisotropy to the effective magnetic anisotropy energy of hexagonal close-packed 0001 cobalt films, largely enhancing the perpendicular anisotropy. Due to a weak electronic interaction of the organic molecules with the Co atoms, an increase of surface anisotropy could be explained by the presence of an electric field at the organic-material/Co interface and by modification of surface atoms charge configuration.

The pseudogap (PG) derived from the analysis of the excess conductivity $\sigma'(T)$ in superlattices and double-layer films of $YBa_2Cu_3O_{7-\delta}$-$PrBa_2Cu_3O_{7-\delta}$(YBCO-PrBCO), prepared by pulsed laser deposition, is studied for the first time. The $\sigma'(T)$ analysis has been performed within the local-pair (LP) model based on the assumption of the paired fermion (LPs) formation in the cuprate high-$T_c$ superconductors (cuprates) below the representative temperature $T^*\gg T_c$ resulting in the PG opening. Within the model, the temperature dependencies of the PG, $\Delta^*(T)$, for the samples with different number of the PrBCO layers ($N_{Pr}$) were analyzed in the whole temperature range from $T^*$ down to $T_c$. Near $T_c$, excess conductivity was found to be perfectly described by the Aslamasov-Larkin and Hikami-Larkin (Maki-Thompson term) fluctuation theories, suggesting the presence of superconducting fluctuations in a relatively large (up to 15 K) temperature range above $T_c$. All sample parameters were found to change with increase of $N_{Pr}$, finally resulting in the appearance of the pronounced maximum of $\Delta^*(T)$ at high temperatures. The result is most likely due to increasing influence of the intrinsic magnetism of PrBCO ($\mu_{Pr}\approx 4\,\mu_B$) and suggests the possibility to search in that way the change of interplay between the superconductivity and magnetism in cuprates.

Magneto-optical imaging with an indicator film is used for investigating the magnetic pattern in ferromagnetic material specimens whose optical properties do not allow the direct visualization of their magnetic pattern. The magneto-optical indicator is a ferromagnetic film with low coercitivity that detects the magnetic field from a magnetic source on which it is placed. The measurement of the indicator film is performed with a polarization microscope. In this way, the magnetic pattern generated by ferromagnets, superconductors, or current carrying conductors has been successfully visualized. By means of epitaxial iron garnet films, we obtained the quantitative imaging of the stray field induced by the magnetic microstructure in ferromagnetic films and crystals. The quantitative measurement of the perpendicular component of the magnetic field, obtained by a suitable nonlinear calibration, is demonstrated for single domain walls in ferromagnetic materials (in this paper for manganite and garnet films).

The effect of wire diameter reduction on the critical current density of pristine MgB2 wire was studied. Wires were treated by a hot isostatic pressing method at 570 °C and at pressures of up to 1.1 GPa. It was found that the wire diameter reduction induces an increase of up to 70% in the mass density of the superconducting cores. This feature leads to increases in critical current, critical current density, and pinning force density. The magnitude and field dependence of the critical current density are related to both grain connectivity and structural defects, which act as effective pinning centers. High field transport properties were obtained without doping of the MgB2 phase. A critical current density jc of 3500 A mm−2 was reached at 4 K, 6 T for the best sample, which was a five-fold increase compared to MgB2 samples synthesized at ambient pressure.

We report on depression of superconducting transition temperature of YBa2Cu3O7 (YBCO) layers, when their thickness is reduced in proximity to ferromagnetic insulating La0.885Sr0.115MnO3 (FI-LSMO) layers in [FI-LSMO*8 u.c./YBCO*n u.c.]16 superlattices, where n = 1, 2, 4 and 6 unit cells (u.c.). The thickness of manganite FI-LSMO layers is kept at 8 unit cells. Signature of antiparallel alignment between FI-LSMO layers across YBCO spacer layers was observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Manganite/oxide cuprate supercondutor heterstructures are attractive model system to study coupling and interface effects. After brief summarizing synthesis and characterization this paper presents recent experimental results obtained in investigated manganite/YBa2Cu3O7 heterostructures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The paper reports on an investigation of the superconducting and magnetic properties of a YBa2Cu3O7/La0.67Sr0.33MnO3 bilayer grown on LaAlO3. Beside structural, transport and optical characterisation the magneto-optical analysis was the main tool to study the local properties of the bilayer. The optical analysis shows the twinned structure exhibited by the substrate and the magneto-optical analysis allows visualizing the manganite magnetic domain structure with in plane-field magnetization, divided by domain walls where magnetic moments tilt out of the film plane. After cooling below Tc the domain-wall stray field induces vortex decoration patterns. Under an external magnetic field flux penetration is strongly modulated by the manganite domain walls. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Oxide multilayers composed of ferromagnetic metallic layers of La0.67Sr0.33MnO3 (LSMO) and superconducting cuprate YBa2Cu3O7 (YBCO) were grown on LaAlO3 substrates by high-pressure dc sputtering. We have investigated the structural, transport, and magnetic properties of a series of samples in which the LSMO layer thickness is fixed at eight unit cells and that of YBCO varied from one to six unit cells. The superconducting transition temperature Tc0 determined from the resistance measurement is higher than the temperature of the onset of the diamagnetic response Td0. This result is discussed in the frames of the model proposed by E. B. Sonin and I. Felner [Phys. Rev. B. 57, R14000 (1998)] for a ferromagnetic superconductor. The model suggests the presence of the spontaneous vortex phase in the temperature interval Td0

Heteroepitaxial growth of multilayer thin films of Nd 0.67 Sr 0.33 MnO 3 /YBa 2 Cu 3 O 7 (NSMO/YBCO) by high-pressure sputtering is reported. We found that critical thickness of YBCO layers for the occurrence of superconductivity in multilayered structure is 3 unit cell. The onset of the temperature of diamagnetic response is lower than the zero resistance superconducting transition temperature. Magnetic hysteresis loops show the coexistence of superconductivity and ferromagnetic order at nm length scale.

We have fabricated perovskite superlattices consisting of ferromagnetic metallic oxide Nd 0.67 Sr 0.33 Mn0 3 (NSMO) and superconducting YBa 2 Cu 3 0 7 (YBCO). We have investigated structural, transport and magnetic properties of a series of multilayers, in which the layer thickness of NSMO is fixed and that of YBCO varied from 2 to 6 unit cells. We find that the superconducting phase is suppressed for YBCO layer thickness lower than 3 unit cells in NSMO/YBCO multilayered structure. Magnetic moment versus external magnetic field hysteresis curves shows a coexistence of ferromagnetism and superconductivity nearly in the scale of their characteristic lengths.

An investigation of electrical, magnetic, and microwave properties is presented for Nd1−xSrxMnO3−y (NSMO) thin films. The NSMO thin films were deposited on (100)-oriented LaAlO3 substrates using both high-pressure sputtering and laser-ablation methods. Several films with different doping concentration ranging from 0.17 to 0.33 were tested for microwave loss and their frequency dependence on the dc magnetic field. The films exhibited Curie temperatures ranging from 220 to 60 K, and saturation magnetization from 0.3 to 0.1 T. The feasibility of applications of magnetic perovskites for magnetic tuning of resonators is analyzed and discussed.

A brief overview of the deposition and properties of YBa2Cu3O7 (YBCO) based heterostructures is presented. Emphasis is placed on the assessment of the deposition process and the properties of practical thin films and heterostructures of layered oxides. Besides a reference to the literature we present our recent results concerning deposition, structural and magnetic properties of YBa2Cu3OT/RE1- χ AxMnO3 (YBCO/REMO) heterostructures.

The high pressure d.c. sputtering method has been used to fabricate (YBa/sub 2/Cu/sub 3/O/sub 7//Nd/sub 0.67/Sr/sub 0.33/MnO/sub 3-y/)//sub n/ [(YBCO/NSMO)/sub n/] superlattices. X-ray analyses show c-axis epitaxial growth on LaAlO/sub 3/ (100) substrates. Nd/sub 0.67/Sr/sub 0.33/MnO/sub 3-y/ films are strained due to some difference in lattice parameters between substrate and YBCO sublayers. Magnetization measurements done on single NSMO films show ferromagnetic order below 200 K. Magnetic moment measured for the superlattices below superconducting transition show ferromagnetic order and superconductivity. Such a behavior indicates on the co-existence of superconductivity and ferromagnetism in the total volume of heterostructures, where superconductivity is related to the YBCO sublayer and ferromagnetism to the NSMO sublayer.

A thin‐film sample of YBa2Cu3O7−δ on MgO was irradiated at room temperature with 50‐keV 2H+ (deuterium) to a dose of 1×1016 ions cm−2. The film was mainly c‐axis textured film, ∼360–420 nm thick, deposited by sputtering on 〈100〉 MgO substrate. The as‐implanted sample was divided into several pieces and annealed in a flowing oxygen ambient using (i) a rapid thermal annealing oven, at various temperatures between 450 and 940 °C, and (ii) a conventional annealing furnace, at various temperatures between 100 and 350 °C. Analysis by secondary‐ion mass spectroscopy shows that the implanted 2H is a fast diffuser in the 123 phase. The apparent activation temperature (energy) for 2H release from the initial traps within the YBCO film during the anneal is estimated to be ∼175 °C (∼0.97 eV), which is obviously lower than the apparent activation temperature (energy) for 2H release from the initial traps within the MgO substrate (∼550 °C, i.e., ∼1.78 eV). At 200 °C the diffusivity of 2H in the YBCO film is estimated t...

We evaluate the effects of high pressure during annealing on the structural and superconducting properties of Ag-doped FeSe bulks. The results obtained in this work indicate that the annealing at high pressure increases the critical temperature, upper critical field and irreversibility field due to the improved uniformity and grain connectivity.

Heteroepitaxial growth of multilayer thin films of Nd/sub 1-x/Sr/sub x/MnO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ (NSMO/YBCO) by high pressure sputtering for two doping level of NSMO system is reported. Multilayers containing NSMO oxide layer with lower Curie temperature (with lower doping level) show higher superconducting transition temperatures for fixed YBCO layer thickness. Such observations indicate that the proximity effect in NSMO/YBCO interfaces has a significant influence on the superconducting transition temperature of YBCO layers. Magnetization loops shows the coexistence of superconducting and ferromagnetic order at nm length scale.

A Vibrating Sample Magnetometer (VSM) was used to study the magnetic properties of YBa2Cu3O7−x (YBCO) thin films sputtered onto LaAlO3, SrTiO3 and MgO substrates, before and after ion implantation with deuterium and 16O+. By applying the Bean model, the irreversible magnetisation M, was converted into a critical current density Jc, using a length scale Λ determined from a non-destructive technique, at each temperature. The implantation led to significant changes in the superconducting properties of the films. Most notably, for the deuterium implantation in lower Tc films (84K typically), Tc was enhanced by several degrees and M/Λ was enhanced by 1.1 – 1.25 times. In higher Tc films (92K), Tc and Jc were unaltered at the present fluencies used. A similar observation was made for films with a range of Tc values implanted with 16O+; when the Tc was unaltered after implantation, M/Λ was also unchanged, but where Tc was depressed M/Λ was enhanced by a factor of 2.3. Possible mechanisms are discussed.

Thin films of YBa 2 Cu 3 O 7−δ (YBCO) deposited by sputtering on LaAlO 3 and SrTiO 3 substrates have been implanted with 50 keV 2 H + (deuterium) ions at doses of 1 × 10 12 cm −2 and 1 × 10 16 cm −2 . Depth profiles of the high dose implants obtained by secondary ion mass spectrometry (SIMS) were compared with Monte Carlo simulations (TRIM90) and showed evidence of channelling in the substrates. The superconducting transition temperature, T c , measured by a.c. susceptibility (ACS) disappeared for the high dose implanted samples and X-ray diffractometry (XRD) showed that the YBCO c-axis length had increased, indicating a loss in oxygen content. After annealing the implanted samples with a rapid thermal annealer in O 2 and N 2 atmospheres, SIMS profiles indicated the fast diffusion of deuterium out of the films.

Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7/ c-axis in-plane thin films and YBCO/PrBCO superlattices have been grown on single-crystal [100] and [110] SrTiO/sub 3/ substrates by high-pressure DC sputtering. The orientation of the deposited films is a function of the deposition temperature, T/sub s/. Preliminary studies of the dissipative behavior of the flux line system in the mixed state of YBCO thin films on [110] SrTiO/sub 3/ substrates were performed. Dissipation processes in both Lorentz force free and Lorentz force configurations are discussed in terms of flux dynamics under the influence of the strong pinning potential intrinsic to the layered structure. Preliminary results for a modulated structure composed of layers of YBCO and insulating PrBCO in a-axis orientation and for the first time [110]-oriented YBCO/PrBCO superlattices are presented. >

Transport measurements were made on c -axis orientated thin films of YBa 2 Cu 3 O 7 − x in order to obtain the magnetic field and the temperature dependence of the in-plane critical current density J c ab . By rotating the samples in the external field, the anisotropy of flux pinning was assessed for this material. Sets of J c ( θ , T , B ) curves, obtained for a variety of differently produced samples, allow us to distinguish between intrinsic pinning properties due to the crystal structure and the nature of the superconducting state, which influences the shape of the flux lines, and pinning by defects. A gradual cross-over from a quasi two-dimensional superconducting state at low temperatures to a three-dimensional state at high temperatures is suggested. We analyse the influence of this effect on the temperature, field and angular dependence of J c ab .

Epitaxial c-axis oriented (YBCO)m/(PrBCO)n superlattices have been grown on SrTiO3 (100) substrates using high pressure DC sputtering. The modulation length Lambda =(mY+nPr) is varied between 2.3 nm and 12.0 nm. Satellite peaks up to third order have been observed in X-ray diffraction. The critical current density jc (B,T, phi ) of such YBCO/PrBCO heterostructures has been measured between 4.5 K to 90 K in magnetic fields up to 6 T and as a function of field direction phi . Measurements have been carried out for a range of modulation lengths. Even for an ultrafine modulation length Lambda =4.5 nm (Y:Pr=1:3), the superlattice has a high critical current density of the order 3.8*106 Acm-2 at low temperatures. The resistive transition in a magnetic field was measured for range of Lambda in order to evaluate possible dependence of the pinning activation energy on the sample structure. The results show that samples with larger decoupling exhibit a lower activation energy.

3 pages Erreur sur l'affiliation : CEA/DSM/IRAMIS et non CEA/DSM/DRECAM; International audience; We report on results of direct microwave absorption measurements of Re1−x Bx MnO3 /YBa2 Cu3 O7−δ half metal/d-wave superconductor superlattices (where Re - La and Pr) and (B - Sr and Ca) for microwave frequencies in the range from 9 to 20 GHz. The measurements of the entire heterostructure were performed mostly at temperatures below the superconducting transition. The obtained results strongly depend on the microwave frequency and can be qualitatively described within the theoretical model of high-frequency properties of Josephson junctions with a ferromagnetic barrier proposed by S. Takahashi, S. Hikino, M. Mori, J. Martinek, and S. Maekawa, Phys. Rev. Lett. 99, 057003 (2007).

We report on results of conductance spectroscopy measurements in the current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries ([001] and [100] directions respectively) of ${\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_{3}/{\text{YBa}}_{2}{\text{Cu}}_{3}{\text{O}}_{7}/{\text{La}}_{0.7}{\text{Sr}}_{0.3}{\text{MnO}}_{3}$ (LSMO/YBCO/LSMO) nonsymmetric trilayer structures in order to search for signature of the formation of spin-triplet phase. This trilayer shows an enhancement of the superconducting transition temperature in magnetic field parallel to the plane. We argue that this enhancement is a result of the formation of spin-triplet phase. The differential conductance $(dI/dV)$ spectra show fully developed zero-bias conductance peaks (ZBCP). The ZBCP measured in CIP geometry demonstrates a sharp shape. This could be attributed to a spin-triplet state arising from the proximity effect at the interface of the half-metal with the $d$-wave superconductor, similar as was predicted theoretically for the $p$-wave superconductor and observed experimentally in $p$-wave ${\text{Sr}}_{2}{\text{RuO}}_{4}$ superconductor. The measurements of the $dI/dV$ in CPP geometry reveal a V shape similar as was experimentally observed in YBCO superconductor and predicted theoretically for superconductor with a ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ pairing symmetry of the order parameter.

We report on the microwave properties of Nd0.67Sr0.33MnO3−x (NSMO) and NSMO/YBa2Cu3O7−x thin film heterostructures. The quality factor (Q) and center frequency of a 13 GHz shielded dielectric cavity resonator, with the film comprising one surface, were measured as functions of temperature and direct current magnetic field. The Q versus field data was theoretically simulated using the Landau–Lifschitz–Gilbert dynamic permeability equation thus demonstrating that the microwave losses are determined by the ferromagnetic properties of the films. Our results indicate that the field-dependent permeability μ(B) of NSMO films holds the potential to create magnetically tunable microwave devices.