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Papers by Yonny Romaguera Barcelay

Advances in Materials Science and Engineering

In this paper, we have performed qualitative and quantitative analysis of LuMnO3 thin films surfa... more In this paper, we have performed qualitative and quantitative analysis of LuMnO3 thin films surfaces, deposited by spin coating over Pt(111)/TiO2/SiO2/Si substrates, to evaluate their spatial patterns as a function of the film’s sintering temperature. Atomic force microscopy was employed to obtain topographic maps that were extensively analyzed via image processing techniques and mathematical tools. 3D (three-dimensional) topographical images revealed that films sintered at 650°C and 750°C presented the formation of smoother surfaces, while the film sintered at 850°C displayed a rougher surface with a root mean square roughness of ∼2.5 nm. On the other direction, the height distribution of the surface for all films has similar asymmetries and shape, although the film sintered using the highest temperature showed the lower density of rough peaks and a sharper peak shape. The advanced fractal parameters revealed that the film sintered at 850°C is dominated by low spatial frequencies, ...

Physica B: Condensed Matter

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Journal of Materials Chemistry A

This work reports the deposition of single phase Bi2ZnTiO6 thin films onto Pt/Si-based substrates... more This work reports the deposition of single phase Bi2ZnTiO6 thin films onto Pt/Si-based substrates using rf-sputtering method and the respective structural, morphological, optical and local ferroelectric characterization. The thin film...

ACS applied materials & interfaces, Jan 8, 2017

Composite materials consisting of two dissimilar ferroic phases are an excellent alternative to s... more Composite materials consisting of two dissimilar ferroic phases are an excellent alternative to single-phase multiferroics for a wide range of magnetoelectric technologies. In composites with strain-mediated magnetoelectric coupling the response is strongly dependent on the characteristics of the interface between the two mechanically coupled phases. Among the different material approaches considered, cofired ceramic composites offer improved reliability in applications and are more adequate for free-forming and miniaturization. However, their magnetoelectric response often suffers from poor reproducibility, which has been reiteratively associated with the quality of the interfaces with little experimental support. Here, we report an in-depth study of the local material properties across the interfaces of 0.36BiScO3-0.64PbTiO3/NiFe2O4 multilayer ceramic composites, processed by spark plasma sintering of nanocrystalline powders. Tailored microstructures and low residual stress levels...

Science and Technology of Advanced Materials, 2015

A highly topical set of perovskite oxides are high-sensitivity piezoelectric ones, among which Pb... more A highly topical set of perovskite oxides are high-sensitivity piezoelectric ones, among which Pb (Zr,Ti)O 3 at the morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal polymorphic phases is reckoned a case study. Piezoelectric ceramics are used in a wide range of mature, electromechanical transduction technologies like piezoelectric sensors, actuators and ultrasound generation, to name only a few examples, and more recently for demonstrating novel applications like magnetoelectric composites. In this case, piezoelectric perovskites are combined with magnetostrictive materials to provide magnetoelectricity as a product property of the piezoelectricity and piezomagnetism of the component phases. Interfaces play a key issue, for they control the mechanical coupling between the piezoresponsive phases. We present here main results of our investigation on the suitability of the high sensitivity MPB piezoelectric perovskite BiScO 3-PbTiO 3 in combination with ferrimagnetic spinel oxides for magnetoelectric composites. Emphasis has been put on the processing at low temperature to control reactions and interdiffusion between the two oxides. The role of the grain size effects is extensively addressed.

Journal of Physics D: Applied Physics, 2014

Epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO) thin films, with different thicknesses ranging from 20 to 33... more Epitaxial La 0.7 Sr 0.3 MnO 3 (LSMO) thin films, with different thicknesses ranging from 20 to 330 nm, were deposited on (1 0 0)-oriented strontium titanate (STO) substrates by pulsed laser deposition, with their structure and morphology characterized at room temperature. The magnetic and electric transport properties of the as-processed thin films reveal an abnormal behaviour in the temperature dependent magnetization M(T) below the antiferrodistortive STO phase transition (T STO), and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Films with thickness ≤100 nm show an in-excess magnetization and pronounced changes in the coercivity due to the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below T STO. However, in thicker LSMO thin films, an in-defect magnetization is observed. This reversed behaviour can be understood with the emergence in the upper layer of the film, of a columnar structure needed to relax the elastic energy stored in the film, which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a full suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behaviour.

Materials Letters, 2012

ABSTRACT This work is addressed to studying GdMnO3 thin films, prepared by a chemical solution me... more ABSTRACT This work is addressed to studying GdMnO3 thin films, prepared by a chemical solution method on oriented Pt substrates. Alterations regarding structure and magnetic response of both ceramics and single crystals show that the behaviour of the as-prepared films can be understood by assuming a continuously changing of the in-plane stress state in the film induced by mechanical coupling with the substrate. The emerging of a ferromagnetic response in the thin films is a consequence of the structural deformations induced by matching both film and substrate during the growth process, which alters the balance between competitive antiferromagnetic and ferromagnetic interactions.

Journal of Physics: Condensed Matter, 2013

This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO ... more This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO 3. The differences in the corresponding phase boundaries in the (x, T) phase diagram could be overcome by considering a scaling of the Y 3+ and Lu 3+ concentrations to the tolerance factor. This outcome evidences that the tolerance factor is in fact a more reliable representative of the lattice deformation induced by doping. The normalization of the phase boundaries using the tolerance factor corroborates previous theoretical outcomes regarding the key role of competitive FM and AFM exchanges in determining the phase diagrams of manganite perovskites. However, significant differences in the nature and number of phases at low temperatures and concentrations could not be explained by just considering the normalization to the tolerance factor. The vertical phase boundary observed just for Lu-doped EuMnO 3 , close to 10% Lu, is understood by considering a low temperature Peierls-type spin-phonon coupling, which stabilizes the AFM-4 phase in Lu-doped EuMnO 3 .

Journal of Electroceramics, 2011

A novel and general chemical solution route for processing high-quality transition metal and rare... more A novel and general chemical solution route for processing high-quality transition metal and rare-earth orthorhombic manganite thin films on Pt(111)/Ti/SiO 2 /Si substrates was reported. The precursor solutions decomposition process of the manganites was studied by TG and DTA techniques, showing the formation of the phase above 650°C in LaMnO 3 and 750°C in both EuMnO 3 and DyMnO 3 thin films. X-ray diffraction and Raman spectroscopic analysis reveal the formation of a pure orthorhombic structure, with a space group Pbnm, in LaMnO 3 , EuMnO 3 and DyMnO 3 thin films annealed at temperatures above the TG phase formation temperature observed. Microstructure and grain morphology of the films were analyzed by SEM and AFM techniques, showing a progressive improvement of the films structures with the increase of the annealing temperature. The temperature dependence of the magnetic response of the LaMnO 3 , EuMnO 3 and DyMnO 3 thin films show typical transition temperatures, compared with those reported for lanthanum, europium and dysprosium manganite single crystals and ceramics.

Journal of Applied Physics, 2013

Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputterin... more Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO 2 /Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K 2 O rich KTaO 3 targets and specific deposition conditions, KTaO 3 d oxygen deficient thin films with a K/Ta ¼ 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO 3 d thin films are under a compressive strain of 2.3% relative to KTaO 3 crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below T pol $ 367 C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above T pol , the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.

Hexagonal LuMnO 3 thin films have been prepared based on a chemical solution deposition method. T... more Hexagonal LuMnO 3 thin films have been prepared based on a chemical solution deposition method. These films were deposited by spin-coating technique and annealed at different temperatures from 750°C up to 850°C, based on the thermogravimetric and differential thermal analysis results. An amorphous phase is observed in the film annealed at 750°C, while a pure LuMnO 3 hexagonal phase is reached in the films annealed at 800°C and 850°C, along with a visible enhancement in the grain morphology as the annealing temperature increase. Low temperature magnetic analysis of the LuMnO 3 films annealed at 850°C reveals several magnetic transitions, which are consistent with those reported for both LuMnO 3 ceramics and single crystals. Moreover, the emergence of a canted spin arrangement was evidenced from the temperature dependence of the specific induced magnetization and magnetic hysteretic cycles. No significant effect of the substrate on the magnetic properties was also sorted out. Dielectric measurements reveal the existence of a complex frequency behavior of the dielectric permittivity, which can be associated with relaxation processes arising from the interfaces film/electrodes.