Person: González Calbet, José María
Loading...
First Name
José María
Last Name
González Calbet
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
15 results
Search Results
Now showing 1 - 10 of 15
Item New insights into the luminescence properties of a Na stabilized Ga-Ti oxide homologous series(Journal of materials chemistry C, 2020) García Fernández, Javier; García Carrión, Marina; Torres Pardo, María De La Almudena; Martínez Casado, María Ruth; Ramírez Castellanos, Julio; Nogales Díaz, Emilio; González Calbet, José María; Méndez Martín, María BianchiHerein, we achieve the synthesis and structural study of a luminescent Na-stabilized Ga-Ti oxide homologous series by atomically resolved electron microscopy. Relevant optical properties as a function of the titanium content have been revealed. In particular, the excitation and emission bands change with the series term, showing wide tunability of the luminescence bands, ranging from the ultraviolet to the infrared. First principles studies of these structures have been done in the framework of density functional theory (DFT) to understand the optical properties. Good agreement with the experimental measurements for the three synthesized terms has been obtained from the perspective of the composition and occupancy of the crystallographic sites, as well as from the energy band structure point of view. This work paves the way to explore further the capabilities of tuning the electronic and optical properties in a variety of application fields.Item Interface double-exchange ferromagnetism in the Mn-Zn-O system: New class of biphase magnetism(Physical review letters, 2005) García, M. A..; Ruiz González, María Luisa; Quesada, A.; González Calbet, José María; Hernando Grande, AntonioIn this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn^(3+) and Mn^(4+) via a double-exchange mechanism. The presence of the ZnO around MnO_2 modifies the kinetics of MnO_2 →Mn_2O_3 reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples.Item Large intrinsic anomalous Hall effect in SrIrO_3 induced by magnetic proximity effect(Nature communications, 2021) Yoo, Myoung-Woo; Tornos Castillo, Javier; Sander, A.; Lin, Ling-Fang; Mohanta, Narayan; Peralta Somoza, Andrea; Sánchez Manzano, David; Gallego Toledo, Fernando; Haskel, D.; Freeland, J. W.; Keavney, D. J.; Choi, Y.; Strempfer, J.; Wang, X.; Cabero Piris, Mariona; Vasili, Hari Babu; Valvidares, Manuel; Sánchez Santolino, Gabriel; González Calbet, José María; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Rosenkranz, S.; Bibes, M.; Barthelemy, A.; Anane, A.; Dagotto, E.; Okamoto, S.; te Velthuis, S. G. E.; Santamaría Sánchez-Barriga, JacoboThe anomalous Hall effect (AHE) is an intriguing transport phenomenon occurring typically in ferromagnets as a consequence of broken time reversal symmetry and spin-orbit interaction. It can be caused by two microscopically distinct mechanisms, namely, by skew or side-jump scattering due to chiral features of the disorder scattering, or by an intrinsic contribution directly linked to the topological properties of the Bloch states. Here we show that the AHE can be artificially engineered in materials in which it is originally absent by combining the effects of symmetry breaking, spin orbit interaction and proximity-induced magnetism. In particular, we find a strikingly large AHE that emerges at the interface between a ferromagnetic manganite (La_(0.7)Sr_(0.3)MnO_3) and a semimetallic iridate (SrIrO_3). It is intrinsic and originates in the proximity-induced magnetism present in the narrow bands of strong spin-orbit coupling material SrIrO_3, which yields values of anomalous Hall conductivity and Hall angle as high as those observed in bulk transition-metal ferromagnets. These results demonstrate the interplay between correlated electron physics and topological phenomena at interfaces between 3d ferromagnets and strong spin-orbit coupling 5d oxides and trace an exciting path towards future topological spintronics at oxide interfaces. The anomalous Hall effect (AHE) occurs in ferromagnets caused by intrinsic and extrinsic mechanisms. Here, Yoo et al. report large anomalous Hall conductivity and Hall angle at the interface between a ferromagnet La_(0.7)Sr_(0.3M)nO_3 and a semimetallic SrIrO_3, due to the interplay between correlated physics and topological phenomena.Item Complex structural ordering of the oxygen deficiency in La_-0.5 Ca_2.5Mn_2O_7-delta Ruddlesden-Popper phases(Acta crystallographica a-foundation and advances, 2019) González Merchante, Daniel; Cortés Gil, Raquel; Alonso Rodríguez, José María; Matesanz Sáez, Emilio; Rivera Calzada, Alberto Carlos; Santamaría Sánchez-Barriga, Jacobo; Ruiz González, María Luisa; González Calbet, José MaríaRuddlesden-Popper oxides, (AO)(ABO_3))_n, occupy a prominent place in the landscape of materials research because of their intriguing potential applications. Compositional modifications to the cation sublattices, A or B, have been explored in order to achieve enhanced functionalities. However, changes to the anionic sublattice have been much less explored. In this work, new oxygen-deficient manganese Ruddlesden-Popper-related phases, La_0.5Ca_2.5Mn_2O_6.5, and La_0.5Ca_2.5Mn_2O_6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La_0.5Ca_2.5Mn_2O_7. A complete structural and compositional characterization, by means of neutron diffraction, electron diffraction and atomically resolved scanning transmission electron microscopy and electron energy-loss spectroscopy techniques, allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO_2] layers along [031] and [013] directions. The gradual decrease of the Mn oxidation state, accommodated by short-range ordering of anionic vacancies, reasonably explains the breaking of ferromagnetic interactions reinforcing the emergence of antiferromagnetic ones. Additional short-range order-disorder phenomena of La and Ca cations have been detected in the reduced La_0.5Ca_2.5Mn_2º_7-delta, as previously reported in the parent compound.Item Temperature dependence of the magnetic properties in LaMnO_(3+δ)(Journal of applied physics, 2006) Romero, J.J.; Cuadrado, R.; Arroyo, A.; García, M. A.; Hernando Grande, Antonio; Cortés Gil, R; González Calbet, José María; Vallet Regí, María Dulce NombreData are presented on the thermal dependence of the hysteretic properties of cationic vacancies including manganite samples of composition LaMnO_(3+δ)(δ=0.05 and 0.12). Our results evidence the presence in both samples of two magnetic phases having ferro- and antiferromagnetic orders, respectively. The temperature dependence of the coercivity and relaxational properties of the samples is closely linked to the connectivity of the magnetic moment bearing Mn^(3+)-Mn^(4+) ferromagnetic clusters that demagnetize independently in the case of the δ=0.05 sample and collectively in that of the δ=0.12 one, as evidenced from the activation volume results (delta=0.05) which yielded a size of the same order magnitude as that obtained in previous works for the Mn^(3+)-Mn^(4+) ferromagnetic cluster size.Item Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet(Nature Materials, 2022) Sanchez Manzano, David; Cuéllar Jiménez, Fabian Andrés; Cabero Piris, Mariona; Rouco Gómez, Víctor; Orfila Rodríguez, Gloria; Tornos Castillo, Javier; Rivera Calzada, Alberto Carlos; González Calbet, José María; León Yebra, Carlos; Villegas Hernández, Javier Eulogio; Santamaría Sánchez-Barriga, JacoboThe Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing. Josephson coupling over micrometres and at tens of kelvins is demonstrated across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7.Item The controlled transition-metal doping of SnO_2 nanoparticles with tunable luminescence(CrystEngComm, 2014) Peche Herrero, M. A.; Maestre Varea, David; Ramírez Castellanos, J.; Cremades Rodríguez, Ana Isabel; Piqueras De Noriega, Francisco Javier; González Calbet, José MaríaSnO_2 nanoparticles doped with transition metals (V, Cr, Mn) have been synthesized by both the hydrothermal method (HDT) in a basic media and the liquid mixed method (LQM) based on the Pechini method. Nanocrystalline particles obtained via a liquid mixed technique show a well-defined chemical composition and an average size of 6 nm, with a high degree of both crystallinity and chemical homogeneity. Nanoparticles prepared via a hydrothermal method exhibit a high dispersion in size as well as agglomeration effects. As the LQM demonstrates advantages with respect to the HDT, a more detailed investigation has been carried out on the SnO_2 nanoparticles doped with V, Cr and Mn grown by this method. The microstructure of the materials was elucidated by means of X-ray Diffraction (XRD), Selected-Area Electron Diffraction (SAED), and High-Resolution Transmission Electron Microscopy (HRTEM). Luminescence from undoped and doped SnO_2 nanoparticles was characterized by cathodoluminescence (CL). The luminescence studies demonstrate a strong dependence of CL signals with transition metal doping, thus inducing red, green or orange emissions when doping with Cr, V or Mn respectively.Item Influence of doping and controlled sn charge state on the properties and performance of SnO nanoparticles as anodes in li-ion batteries(Journal of physical chemistry C, 2020) Vázquez López, Antonio; Maestre Varea, David; Ramírez Castellanos, Julio; González Calbet, José María; Pís, Igor; Nappini, Silvia; Yuca, Neslihan; Cremades Rodríguez, Ana IsabelLi-ion batteries (LiB) play nowadays a major role in several technological fields. In addition to enhanced high capacity and long cyclability, some other issues regarding safety, materials sustainability, and low cost remain unsolved. Tin oxide (SnO_2) presents several of those advantages as an anode material; however, some aspects still require to be investigated such as capacity fading over cycles. Herein, tin oxide nanoparticle-based anodes have been tested, showing high capacities and a significant cyclability over more than 150 cycles. A complementary strategy introducing doping elements such as Li and Ni during the synthesis by hydrolysis has been also evaluated versus the use of undoped materials, in order to assess the dependence on SnO_2 quality and properties of battery performance. Diverse aspects such as the Sn charge state in the synthesized nanoparticles, the variable incorporation of dopants, and the structure of defects have been considered in the understanding of the obtained capacity.Item Study of the defects in sintered SnO_2 by high-resolution transmission electron microscopy and cathodoluminescence(European Journal of Inorganic Chemistry, 2007) Maestre Varea, David; Ramirez Castellanos, Julio; Hidalgo Alcalde, Pedro; Cremades Rodríguez, Ana Isabel; González Calbet, José María; Piqueras De Noriega, Francisco JavierThe defect structure of sintered SnO_2 was investigated by high-resolution transmission electron microscopy (HRTEM), cathodoluminescence (CL), and electrical measurements. HRTEM shows the presence of the SnO phase in the sintered samples as well as twinning, stacking faults, and disordered intergrowths. The sintered samples annealed under an oxygen atmosphere show changes in the defect structure and in the CL spectra. In particular, the intensity of a CL band at 1.94 eV, related to oxygen vacancies, decreased as the electrical resistivity increased. The results are discussed by considering the presence of stoichiometric defects such as oxygen vacancies and Sn interstitials in the final structure and their evolution during the annealing process under an oxygen atmosphere.Item Magnon-mediated magnetoresistance in layered manganites(Physical review B, 2019) Hernando Grande, Antonio; Cortés Gil, Raquel; González Merchante, Daniel; Hernando González, María; Alonso Rodríguez, José María; García García Tuñón, Miguel Ángel; Martínez, José L.; Ruiz Gonález, María Luisa; González Calbet, José MaríaWe describe here a type of magnetoresistance that takes place in naturally layered and outstanding ordered single phase manganites that may be mediated by magnon excitation. In particular, we show the effect for the Ruddlesden-Popper compound, LaSr2Mn2O7 synthesized by ceramic method. This material exhibits, besides the conventional colossal magnetoresistance, another type of magnetoresistance at low temperature, associated with breaking of the A-type antiferromagnetic coupling of Mn-containing planes. Excitation of magnons or application of a magnetic field breaks this antiparallel alignment so that some electrons, initially confined on the planes, become itinerant along the interplain directions through a double exchange mechanism, giving rise to resistance variations of the order of similar to 60% for polycrystalline samples. The effect described here might be present in other types of manganites exhibiting a natural layered structure, opening up the possibility of developing magnetoresistive devices based on antiferromagnetic oxide materials without requiring artificial multilayered structures.