95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 and electron-doped Sr 2... more 95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 and electron-doped Sr 2-x La x FeMoO 6 ceramics. Detailed analysis of the NMR spectra from pristine Sr 2 FeMoO 6 conclusively shows that the Mo hyperfine field is mainly due to atomic Mo magnetic moments. No contribution of transferred hyperfine field has been observed, confirming the absence of s-electrons in the conduction band. Upon La doping, the NMR frequency (hyperfine field) gradually increases proving that the concentration of spin polarized electrons at Mo ion is enhanced by the La substitution. A simple linear correlation between magnetic moment at Mo sites and the Curie temperature of the system has been found. Implications for understanding the electronic structure and the ferromagnetic coupling in these systems are underlined.
One of the current frontiers in magnetism is to understand the domain structure and the magnetiza... more One of the current frontiers in magnetism is to understand the domain structure and the magnetization reversal in nanometer-sized particles. Explorations at these length scales have been aided by the development of new magnetic imaging techniques [1], one of which is the magnetic force microscope (MFM), a variant of the atomic force microscope. We have utilized the high resolution MFM (30 nm) we developed [2] to increase our fundamental understanding of magnetism on this length scale. I will discuss the field-induced magnetic reversal in particles on the order of hundreds of nanometers in width and about twice that in length. In general, for the small aspect (length to width) ratio, the magnetization reverses by the formation of a single vortex and its propagation down the length of a particle (when the fields are applied perpendicular to the long axis). There are some surprises when the aspect ratio of the particles increases.
We show that atomically flat single SrO-terminated SrTiO3(001) substrates can be obtained through... more We show that atomically flat single SrO-terminated SrTiO3(001) substrates can be obtained through simple high-temperature treatment. Amplitude-modulation atomic force microscopy with phase-lag analysis and x-ray photoelectron spectroscopy, have been used to demonstrate that the ratio between the two chemical terminations can be tailored by choosing the annealing time. Moreover, the progressive SrO surface enrichment (up to 100%) is accompanied by a self-assembly process which results in the spatial separation at the nanoscale of both chemical terminations. We further demonstrate that this opens a interesting avenue for selective chemical reaction and growth of oxide nanostructures.
We report on the optical response of different magnetic oxides (manganites, ruthenates, and magne... more We report on the optical response of different magnetic oxides (manganites, ruthenates, and magnetite) and show that for photons with energies 1.5−3.5 eV the intensity of light reflected by these epitaxial oxide thin films is strongly modulated by magnetic fields. We argue that this behavior is related to the magnetopolaron physics, and the magnitude of the magnetoreflectance is a fingerprint and a measure of the electron-lattice coupling strength. Our research provides the basis for a fresh experimental approach to the physics of strongly correlated electronic systems.
IEEE Transactions on Appiled Superconductivity, 1997
Ahtract-In order to obtain high-power hzuidlirig, dual-nlode patch HTS filters have been analyzed... more Ahtract-In order to obtain high-power hzuidlirig, dual-nlode patch HTS filters have been analyzed through Green's function rad desegmentation techniques. A precise circuit model has been obtained and applied to the filter design process, and useful design curves relating filter parameters and physical dimensions of the square patch have been plotted. Several designs have been made using them and then optimized with the Method of Moments in the Spectral Domain. For higher order circuits, staggered coupled-line HTS filters have been considered. The designs have been made using the method of moments to compute the coupling capacitances, and then optimized with the Method of Moments in the Spectral Domain. One dual-mode patch filter and ane staggered coupled-iine filter have been fabricated on a YBCO film. Measurements agree well with simulations.
ABSTRACT Pellets of YBCO HTSC have been used to construct a cylindrically shaped rotor. A four po... more ABSTRACT Pellets of YBCO HTSC have been used to construct a cylindrically shaped rotor. A four poles/four phases stator has been wound in order to build a motor. The motor behaves as an hysteresis motor when it starts and as synchronous in the steady state. The levitation forces associated to the flux inside the rotor region and the flux dispersed at the basal surfaces contribute to maintain the rotor anchored to its cavity in a self-sustained configuration. Power and torque in the synchronous regime, centering forces, static excitation field mapping and field distribution at the HTSC surface have been investigated.
The magnetotransport properties of the Tl 2 Mn 2-x Ru x O 7 pyrochlore are studied. It is shown t... more The magnetotransport properties of the Tl 2 Mn 2-x Ru x O 7 pyrochlore are studied. It is shown that Ru 4+ substitution in the Mn 4+ network provides a convenient way to modify the charge density in the Tl-O band without disrupting it with foreign cations. The experimental data ...
We report on the progress on computing the current maps from the magnetic induction in bulk sampl... more We report on the progress on computing the current maps from the magnetic induction in bulk samples of YBCO melt-textured compounds. Typical sample size is in the cm range and induction maps B z ðx; y; zÞ are obtained by Hall probe measurements. Currents are obtained by solving the inverse Biot-Savart problem. No assumption is required on the number of domains or geometry of the sample; the only constraint in the model is that the current circulation should be confined in the basal plane and uniform in the sample thickness. A current map with a resolution of 0.25-0.5 mm is typically obtained. Critical tests of the stability and accuracy of the current flow solutions have been performed. We have applied the algorithms to remanent flux maps obtained after both FC and ZFC magnetization processes. The algorithms can be readily used and thus can constitute a helpful tool for superconductivity engineers. The use of our software implementation is available free of charge at http://jaumetor.upc.es:8080/caragol.
Abstract Magnetically modulated microwave absorption (MAMMA) measurements have been performed on ... more Abstract Magnetically modulated microwave absorption (MAMMA) measurements have been performed on a superconducting Sm2−xCexCuO4−δ single crystal by sweeping the temperature at constant magnetic fields applied in different orientations. The result of each measurement is a well-defined peak, whose onset determines, in a mean field approximation, the superconducting transition. We have found that the characteristics of the MAMMA signal at any field orientation (H, θ) can be described in terms of a reduced field h = H ( cos 2 θ + γ 2 sin 2 θ) 1 2 , where γ is the anisotropy parameter. The scaling of the experimental data has allowed us to determine γ ≈ 75.
... 64 (1987) 707. 9) L. Civolle, H. Sagar, F. de la Cruz, DA Espar za, CA D'Ovidio; Solid S... more ... 64 (1987) 707. 9) L. Civolle, H. Sagar, F. de la Cruz, DA Espar za, CA D'Ovidio; Solid State Comm. 65 (1987~ 129. i0) TH Lin, .V. Shoo, MK Wu, PH Hot, XC Ji~, CW Chu~ N. Evans, R. Baynzick; Phys. Rev. B2Q (198#) 1493. II) G. Deutscher, KA Muller; Phys. Rev. kett. ...
We have investigated the anisotropic magnetoresistance (AMR) and the anomalous Nernst effect (ANE... more We have investigated the anisotropic magnetoresistance (AMR) and the anomalous Nernst effect (ANE) in an exchange-biased bilayer consisting of a thin film of permalloy deposited on a single crystal antiferromagnetic NiO (100). The exchange bias field (H EB) value was obtained by means of AMR, ANE and magnetization hysteresis measurements. The shift of the hysteresis loop, measured with the three different techniques, yield approximately the same value of H EB. In spite of the measurement techniques be based in different physical phenomena, our results confirm the robustness of the exchange anisotropy at the Py/NiO interface. The strength of the anomalous Nernst effect for the exchange-biased permalloy film is compared to values measured in non biased films.
Epitaxial orthorhombic YMnO 3 thin films, (0 0 1) oriented, have been grown by pulsed laser depos... more Epitaxial orthorhombic YMnO 3 thin films, (0 0 1) oriented, have been grown by pulsed laser deposition on (0 0 1)SrTiO 3 substrates. Their crystal structure and magnetic response have been studied in detail. Although bulk o-YMnO 3 is antiferromagnetic, our magnetic measurements reveal intriguing thermal hysteresis between the zero-field-cooled and field-cooled curves below the onset of the antiferromagnetic ordering temperature, thus signaling a more complex magnetic structure with net ferromagnetic moments. We discuss on the possible origin of this net magnetization and we have found a correlation of the magnetic response with the strain state of the films. We propose that substrate-induced strain modifies the subtle competition of magnetic interactions and leads to a non-collinear magnetic state that can thus be tuned by strain engineering.
95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 ceramic powders contain... more 95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 ceramic powders containing from 3% up to 28% of Mo-Fe antisites. Hyperfine fields and the on site magnetic moment on molybdenum were found to be insensitive to the cationic disorder. Magnetic stiffness and the NMR restoring field increased by an order of magnitude between 3% and 28% of antisite concentration.
La Sr MnO perovskite (LSMO), which shows a ferromagnetic transition above room temperature, is a ... more La Sr MnO perovskite (LSMO), which shows a ferromagnetic transition above room temperature, is a good candidate to be used as a magnetoresistive sensor. Magnetic and transport properties of granular LSMO have been studied. Di!erent grain size and the use of metal/insulator composites have been explored in order to optimize the magnetoresistive response. LSMO ceramic powder have been used to prepare thick "lms on polycrystalline Al O substrates by screen printing. The magnetoresistive response of the grown thick "lms is analyzed in the range of technical "elds. It is shown, that under appropriate conditions, materials having "eld sensitivity high enough for some applications at room temperature can be obtained. A magnetic sensor has been developed in order to show the feasibility of this material as a low-cost magnetic sensor.
ABSTRACT The electrical resistivity of granular nanometric La2/3Sr1/3MnO3 ceramics is studied as ... more ABSTRACT The electrical resistivity of granular nanometric La2/3Sr1/3MnO3 ceramics is studied as a function of temperature and magnetic field. Both low-field (LFMR) and high-field (HFMR) magnetoresistance response have been measured as a function of the grain size (∅). The behavior of the LFMR and HFMR responses turns out to be substantially different: whereas LFMR saturates at a value of about 30% for grain sizes ∅≈400 nm, with no increase with further reduction of the grain size, the HFMR progressively increases as the grain size is reduced. Experimental data indicates that HFMR originates from the existence of a non-collinear ferromagnetic surface layer with a thickness that increases as ∅ decreases. The results can be analyzed within the framework of a model involving the existence of a Coulomb gap EC, superimposed to a tunneling barrier between individual grains, which produces a significant blockade at temperatures below ∼100 K. Detailed data analysis allows to separate the contributions from tunneling and Coulomb gap and to determine its value and the grain size and magnetic field dependence.
Epitaxial films of the biferroic YMnO 3 (YMO) oxide have been grown on platinum-coated SrTiO 3 (1... more Epitaxial films of the biferroic YMnO 3 (YMO) oxide have been grown on platinum-coated SrTiO 3 (1 1 1) and Al 2 O 3 (0 0 0 1) substrates. The platinum electrodes, (1 1 1) oriented, are templates for the epitaxy of the hexagonal phase of YMO with a (0 0 0 1) out-of-plane orientation, which is of interest as this is the polarization direction of YMO. X-ray diffractometry indicates the presence of two crystal domains, 601 rotated in-plane, in the Pt(1 1 1) layers which subsequently are transferred on the upperlaying YMO. Cross-section analysis by high-resolution transmission electron microscopy (HRTEM) of YMnO 3 /Pt/SrTiO 3 (1 1 1) shows high-quality epitaxy and sharp interfaces across the structure in the observed region. We present a detailed study of the epitaxial growth of the hexagonal YMO on the electrodes.
95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 and electron-doped Sr 2... more 95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 and electron-doped Sr 2-x La x FeMoO 6 ceramics. Detailed analysis of the NMR spectra from pristine Sr 2 FeMoO 6 conclusively shows that the Mo hyperfine field is mainly due to atomic Mo magnetic moments. No contribution of transferred hyperfine field has been observed, confirming the absence of s-electrons in the conduction band. Upon La doping, the NMR frequency (hyperfine field) gradually increases proving that the concentration of spin polarized electrons at Mo ion is enhanced by the La substitution. A simple linear correlation between magnetic moment at Mo sites and the Curie temperature of the system has been found. Implications for understanding the electronic structure and the ferromagnetic coupling in these systems are underlined.
One of the current frontiers in magnetism is to understand the domain structure and the magnetiza... more One of the current frontiers in magnetism is to understand the domain structure and the magnetization reversal in nanometer-sized particles. Explorations at these length scales have been aided by the development of new magnetic imaging techniques [1], one of which is the magnetic force microscope (MFM), a variant of the atomic force microscope. We have utilized the high resolution MFM (30 nm) we developed [2] to increase our fundamental understanding of magnetism on this length scale. I will discuss the field-induced magnetic reversal in particles on the order of hundreds of nanometers in width and about twice that in length. In general, for the small aspect (length to width) ratio, the magnetization reverses by the formation of a single vortex and its propagation down the length of a particle (when the fields are applied perpendicular to the long axis). There are some surprises when the aspect ratio of the particles increases.
We show that atomically flat single SrO-terminated SrTiO3(001) substrates can be obtained through... more We show that atomically flat single SrO-terminated SrTiO3(001) substrates can be obtained through simple high-temperature treatment. Amplitude-modulation atomic force microscopy with phase-lag analysis and x-ray photoelectron spectroscopy, have been used to demonstrate that the ratio between the two chemical terminations can be tailored by choosing the annealing time. Moreover, the progressive SrO surface enrichment (up to 100%) is accompanied by a self-assembly process which results in the spatial separation at the nanoscale of both chemical terminations. We further demonstrate that this opens a interesting avenue for selective chemical reaction and growth of oxide nanostructures.
We report on the optical response of different magnetic oxides (manganites, ruthenates, and magne... more We report on the optical response of different magnetic oxides (manganites, ruthenates, and magnetite) and show that for photons with energies 1.5−3.5 eV the intensity of light reflected by these epitaxial oxide thin films is strongly modulated by magnetic fields. We argue that this behavior is related to the magnetopolaron physics, and the magnitude of the magnetoreflectance is a fingerprint and a measure of the electron-lattice coupling strength. Our research provides the basis for a fresh experimental approach to the physics of strongly correlated electronic systems.
IEEE Transactions on Appiled Superconductivity, 1997
Ahtract-In order to obtain high-power hzuidlirig, dual-nlode patch HTS filters have been analyzed... more Ahtract-In order to obtain high-power hzuidlirig, dual-nlode patch HTS filters have been analyzed through Green's function rad desegmentation techniques. A precise circuit model has been obtained and applied to the filter design process, and useful design curves relating filter parameters and physical dimensions of the square patch have been plotted. Several designs have been made using them and then optimized with the Method of Moments in the Spectral Domain. For higher order circuits, staggered coupled-line HTS filters have been considered. The designs have been made using the method of moments to compute the coupling capacitances, and then optimized with the Method of Moments in the Spectral Domain. One dual-mode patch filter and ane staggered coupled-iine filter have been fabricated on a YBCO film. Measurements agree well with simulations.
ABSTRACT Pellets of YBCO HTSC have been used to construct a cylindrically shaped rotor. A four po... more ABSTRACT Pellets of YBCO HTSC have been used to construct a cylindrically shaped rotor. A four poles/four phases stator has been wound in order to build a motor. The motor behaves as an hysteresis motor when it starts and as synchronous in the steady state. The levitation forces associated to the flux inside the rotor region and the flux dispersed at the basal surfaces contribute to maintain the rotor anchored to its cavity in a self-sustained configuration. Power and torque in the synchronous regime, centering forces, static excitation field mapping and field distribution at the HTSC surface have been investigated.
The magnetotransport properties of the Tl 2 Mn 2-x Ru x O 7 pyrochlore are studied. It is shown t... more The magnetotransport properties of the Tl 2 Mn 2-x Ru x O 7 pyrochlore are studied. It is shown that Ru 4+ substitution in the Mn 4+ network provides a convenient way to modify the charge density in the Tl-O band without disrupting it with foreign cations. The experimental data ...
We report on the progress on computing the current maps from the magnetic induction in bulk sampl... more We report on the progress on computing the current maps from the magnetic induction in bulk samples of YBCO melt-textured compounds. Typical sample size is in the cm range and induction maps B z ðx; y; zÞ are obtained by Hall probe measurements. Currents are obtained by solving the inverse Biot-Savart problem. No assumption is required on the number of domains or geometry of the sample; the only constraint in the model is that the current circulation should be confined in the basal plane and uniform in the sample thickness. A current map with a resolution of 0.25-0.5 mm is typically obtained. Critical tests of the stability and accuracy of the current flow solutions have been performed. We have applied the algorithms to remanent flux maps obtained after both FC and ZFC magnetization processes. The algorithms can be readily used and thus can constitute a helpful tool for superconductivity engineers. The use of our software implementation is available free of charge at http://jaumetor.upc.es:8080/caragol.
Abstract Magnetically modulated microwave absorption (MAMMA) measurements have been performed on ... more Abstract Magnetically modulated microwave absorption (MAMMA) measurements have been performed on a superconducting Sm2−xCexCuO4−δ single crystal by sweeping the temperature at constant magnetic fields applied in different orientations. The result of each measurement is a well-defined peak, whose onset determines, in a mean field approximation, the superconducting transition. We have found that the characteristics of the MAMMA signal at any field orientation (H, θ) can be described in terms of a reduced field h = H ( cos 2 θ + γ 2 sin 2 θ) 1 2 , where γ is the anisotropy parameter. The scaling of the experimental data has allowed us to determine γ ≈ 75.
... 64 (1987) 707. 9) L. Civolle, H. Sagar, F. de la Cruz, DA Espar za, CA D'Ovidio; Solid S... more ... 64 (1987) 707. 9) L. Civolle, H. Sagar, F. de la Cruz, DA Espar za, CA D'Ovidio; Solid State Comm. 65 (1987~ 129. i0) TH Lin, .V. Shoo, MK Wu, PH Hot, XC Ji~, CW Chu~ N. Evans, R. Baynzick; Phys. Rev. B2Q (198#) 1493. II) G. Deutscher, KA Muller; Phys. Rev. kett. ...
We have investigated the anisotropic magnetoresistance (AMR) and the anomalous Nernst effect (ANE... more We have investigated the anisotropic magnetoresistance (AMR) and the anomalous Nernst effect (ANE) in an exchange-biased bilayer consisting of a thin film of permalloy deposited on a single crystal antiferromagnetic NiO (100). The exchange bias field (H EB) value was obtained by means of AMR, ANE and magnetization hysteresis measurements. The shift of the hysteresis loop, measured with the three different techniques, yield approximately the same value of H EB. In spite of the measurement techniques be based in different physical phenomena, our results confirm the robustness of the exchange anisotropy at the Py/NiO interface. The strength of the anomalous Nernst effect for the exchange-biased permalloy film is compared to values measured in non biased films.
Epitaxial orthorhombic YMnO 3 thin films, (0 0 1) oriented, have been grown by pulsed laser depos... more Epitaxial orthorhombic YMnO 3 thin films, (0 0 1) oriented, have been grown by pulsed laser deposition on (0 0 1)SrTiO 3 substrates. Their crystal structure and magnetic response have been studied in detail. Although bulk o-YMnO 3 is antiferromagnetic, our magnetic measurements reveal intriguing thermal hysteresis between the zero-field-cooled and field-cooled curves below the onset of the antiferromagnetic ordering temperature, thus signaling a more complex magnetic structure with net ferromagnetic moments. We discuss on the possible origin of this net magnetization and we have found a correlation of the magnetic response with the strain state of the films. We propose that substrate-induced strain modifies the subtle competition of magnetic interactions and leads to a non-collinear magnetic state that can thus be tuned by strain engineering.
95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 ceramic powders contain... more 95, 97 Mo NMR experiments have been performed on a series of Sr 2 FeMoO 6 ceramic powders containing from 3% up to 28% of Mo-Fe antisites. Hyperfine fields and the on site magnetic moment on molybdenum were found to be insensitive to the cationic disorder. Magnetic stiffness and the NMR restoring field increased by an order of magnitude between 3% and 28% of antisite concentration.
La Sr MnO perovskite (LSMO), which shows a ferromagnetic transition above room temperature, is a ... more La Sr MnO perovskite (LSMO), which shows a ferromagnetic transition above room temperature, is a good candidate to be used as a magnetoresistive sensor. Magnetic and transport properties of granular LSMO have been studied. Di!erent grain size and the use of metal/insulator composites have been explored in order to optimize the magnetoresistive response. LSMO ceramic powder have been used to prepare thick "lms on polycrystalline Al O substrates by screen printing. The magnetoresistive response of the grown thick "lms is analyzed in the range of technical "elds. It is shown, that under appropriate conditions, materials having "eld sensitivity high enough for some applications at room temperature can be obtained. A magnetic sensor has been developed in order to show the feasibility of this material as a low-cost magnetic sensor.
ABSTRACT The electrical resistivity of granular nanometric La2/3Sr1/3MnO3 ceramics is studied as ... more ABSTRACT The electrical resistivity of granular nanometric La2/3Sr1/3MnO3 ceramics is studied as a function of temperature and magnetic field. Both low-field (LFMR) and high-field (HFMR) magnetoresistance response have been measured as a function of the grain size (∅). The behavior of the LFMR and HFMR responses turns out to be substantially different: whereas LFMR saturates at a value of about 30% for grain sizes ∅≈400 nm, with no increase with further reduction of the grain size, the HFMR progressively increases as the grain size is reduced. Experimental data indicates that HFMR originates from the existence of a non-collinear ferromagnetic surface layer with a thickness that increases as ∅ decreases. The results can be analyzed within the framework of a model involving the existence of a Coulomb gap EC, superimposed to a tunneling barrier between individual grains, which produces a significant blockade at temperatures below ∼100 K. Detailed data analysis allows to separate the contributions from tunneling and Coulomb gap and to determine its value and the grain size and magnetic field dependence.
Epitaxial films of the biferroic YMnO 3 (YMO) oxide have been grown on platinum-coated SrTiO 3 (1... more Epitaxial films of the biferroic YMnO 3 (YMO) oxide have been grown on platinum-coated SrTiO 3 (1 1 1) and Al 2 O 3 (0 0 0 1) substrates. The platinum electrodes, (1 1 1) oriented, are templates for the epitaxy of the hexagonal phase of YMO with a (0 0 0 1) out-of-plane orientation, which is of interest as this is the polarization direction of YMO. X-ray diffractometry indicates the presence of two crystal domains, 601 rotated in-plane, in the Pt(1 1 1) layers which subsequently are transferred on the upperlaying YMO. Cross-section analysis by high-resolution transmission electron microscopy (HRTEM) of YMnO 3 /Pt/SrTiO 3 (1 1 1) shows high-quality epitaxy and sharp interfaces across the structure in the observed region. We present a detailed study of the epitaxial growth of the hexagonal YMO on the electrodes.
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