I obtained the PhD degree in Materials Science and Engineering from National University of Mexico (UNAM), in collaboration with University of Paris Diderot. Last year I began my first postdoctoral position at ENSICAEN-CRISMAT, Caen, France, under the advising of Sylvie Hébert. This year, for my second year as postdoc, I am working at GEEPS - Sorbonne Université laboratory, in Paris, under the advice of Hakeim Talleb. I have worked mainly on the obtention and characterization of nanostructured multiferroic composites (oxide ceramics) as well as bulk thermoelectric materials (pyrite type sulfurs), all fully densified by Spark Plasma Sintering.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2019
The strong interplay between magnetism and transport can tune the thermoelectric properties in ch... more The strong interplay between magnetism and transport can tune the thermoelectric properties in chalcogenides and oxides. In the case of ferromagnetic CoS 2 pyrite, it was previously shown that the power factor is large at room temperature, reaching 1 mW m −1 K −2 and abruptly increases for temperatures below the Curie transition ( T C ), an increase potentially due to a magnonic effect on the Seebeck ( S ) coefficient. The too large thermal conductivity approximately equal to 10.5 W m −1 K −1 at room temperature prevents this pyrite from being a good thermoelectric material. In this work, samples belonging to the Co 1− x Fe x S 2 pyrite family ( x = 0, 0.15 and 0.30) have thus been investigated in order to modify the thermal properties by the introduction of disorder on the Co site. We show here that the thermal conductivity can indeed be reduced by such a substitution, but that this substitution predominantly induces a reduction of the electronic part of the thermal conductivity...
ABSTRACT BaTiO3-CoFe2O4 nanocomposites with a 1/1 molar ratio were prepared by a combination of p... more ABSTRACT BaTiO3-CoFe2O4 nanocomposites with a 1/1 molar ratio were prepared by a combination of polyol synthesis (chimie douce) and a subsequent consolidation by spark plasma sintering. The nanocomposite samples, with a grain size about 50 nm showed a good mixing and a high density. Their impedance response was measured in the 5 Hz-1 MHz frequency range, under magnetic fields up to 1200 kA/m. Measurements were carried out in the 40-210 °C temperature range. We used the Jonscher's universal relaxation law to analyze the electric conductivity results. Significant changes in the activation energies for long range conductivity and hopping conductivity were observed both at the coercive magnetic field of the ferrite and the Curie transition of the titanate. We show that the use of impedance spectroscopy, based on a wide frequency range, provides a far larger view of electric phenomena allowing a separation of the several contributions to the conductivity phenomena, as a function of the magnetic field.
The wealth of properties in functional materials at the nanoscale has attracted tremendous intere... more The wealth of properties in functional materials at the nanoscale has attracted tremendous interest over the last decades, spurring the development of ever more precise and ingenious characterization techniques. In ferroelectrics, for instance, scanning probe microscopy based techniques have been used in conjunction with advanced optical methods to probe the structure and properties of nanoscale domain walls, revealing complex behaviours such as chirality, electronic conduction or localised modulation of mechanical response. However, due to the different nature of the characterization methods, only limited and indirect correlation has been achieved between them, even when the same spatial areas were probed. Here, we propose a fast and unbiased analysis method for heterogeneous spatial data sets, enabling quantitative correlative multi-technique studies of functional materials. The method, based on a combination of data stacking, distortion correction, and machine learning, enables a...
There is a great interest to synthesize ferroelectric ceramics both with fine grain size and sign... more There is a great interest to synthesize ferroelectric ceramics both with fine grain size and significant electric properties. Here, we report the preparation of nanostructured tetragonal barium titanate by combining forced hydrolysis of metallic salts in polyol, soft annealing and 650 C spark plasma sintering under uniaxial pressure of 120 MPa for 5 min. The stabilization of highly dense (density of 90%), nanostructured (grains about 50 nm) tetragonal barium titanate ceramic was achieved. The produced ceramic exhibited ferroelectric behavior and a dielectric permittivity of 3600 at 1 kHz and room temperature.
Journal of Spintronics and Magnetic Nanomaterials, 2012
ABSTRACT We report on the synthesis, consolidation, magnetic properties and electrical conductivi... more ABSTRACT We report on the synthesis, consolidation, magnetic properties and electrical conductivity of cobalt ferrite-barium titanate nanostructured ceramics. The precursor oxides were separately synthesized as nanoparticles by the polyol method, namely forced hydrolysis of metallic salts in a polyol solvent, mixed and consolidated by spark plasma sintering at 500 °C for 5 min, limiting grain growth under 100 nm. Hysteresis loops showed evidence of a good mixing as an increase in coercive field as compared to isolated ferrite prepared under the same conditions. Electrical conductivity analyzed on the basis of the Jonscher Universal Law exhibited evidence of phase coupling as the onset of activation energy for hopping conductivity frequency showed a change of slope at the barium titanate transition temperature.
ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by th... more ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase.
We report the synthesis of yttrium iron garnet (YIG) combining soft chemistry route, namely the p... more We report the synthesis of yttrium iron garnet (YIG) combining soft chemistry route, namely the polyol process, and spark plasma sintering (SPS) technique. The polyol process produced an intermediary amorphous phase containing both iron and yttrium cations in the desired ratio. They were annealed at 400°C in air to decompose the organic content of the reaction (polyol and acetate). To achieve the garnet phase, the polyol-obtained precursor was subjected to reactive SPS treatment at a temperature of 750°C, far below the typical temperatures (1350°C) used in the classic solid-state reaction process. In 15 min pure and high-density Y 3 Fe 5 O 12 ceramic, with about 100 nm sized crystalline grains, was obtained. We report as well the characterization of the initial amorphous phase and the obtained YIG by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, 57 Fe M€ ossbauer spectrometry, and magnetization measurements.
ABSTRACT Multiferroic systems formed by a mixing of a ferroelectric phase and a ferrimagnetic pha... more ABSTRACT Multiferroic systems formed by a mixing of a ferroelectric phase and a ferrimagnetic phase are receiving significant attention because of their wide possibilities for tailoring properties. In this work, the magnetic properties of the cobalt ferrite-barium titanate system were investigated on samples prepared by an original combination of synthesis methods. Cobalt ferrite and barium titanate nanoparticles were synthesized separately by hydrolysis of the metal acetates in a polyol method. Both materials were mixed in a 1:1 ratio and consolidated by spark plasma sintering at 500 °C for 5 min. A high density nanostructured ceramic was obtained with grains smaller than 100 nm and a density about 80% of the theoretical value. Magnetic hysteresis loops showed a hard magnet behavior, with a coercive field larger than cobalt ferrite alone prepared under the same conditions. δM reversible magnetization plots exhibited dipolar interactions with a maximum at the coercive field. These results are interpreted in terms of an efficient mixing of the components, which strongly decreases the magnetic percolation in the composite by separating ferrite grains by titanate grains.
ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by th... more ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase.
Nanostructured Materials, Edited by Mohindar Seehra, 2017
Ferrites are a well-known class of ferrimagnetic materials. In the form of nanoparticles (NPs), t... more Ferrites are a well-known class of ferrimagnetic materials. In the form of nanoparticles (NPs), they exhibit novel and fascinating properties, leading to an extremely wide variety of applications in electronics, biomedical and environmental fields. These applications result from nanoscale effects on physical properties, particularly magnetic properties. For applications in electronic devices, however, a high-density, consolidated body, with very fine grains is needed, in order to retain the nanoscale properties. To our knowledge, spark plasma sintering (SPS) is the only method permitting a full densification with final grain size in the nanometer range. In this review, we examine the SPS method as applied to ferrites and, in particular, the effects of SPS parameters on the final nanostructures obtained. Due to their technological impact, we also discuss the SPS fabrication of hybrid multiferroic nanostructures composed of a ferrite and a ferroelectric phase.
Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol
... more Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8 nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2019
The strong interplay between magnetism and transport can tune the thermoelectric properties in ch... more The strong interplay between magnetism and transport can tune the thermoelectric properties in chalcogenides and oxides. In the case of ferromagnetic CoS 2 pyrite, it was previously shown that the power factor is large at room temperature, reaching 1 mW m −1 K −2 and abruptly increases for temperatures below the Curie transition ( T C ), an increase potentially due to a magnonic effect on the Seebeck ( S ) coefficient. The too large thermal conductivity approximately equal to 10.5 W m −1 K −1 at room temperature prevents this pyrite from being a good thermoelectric material. In this work, samples belonging to the Co 1− x Fe x S 2 pyrite family ( x = 0, 0.15 and 0.30) have thus been investigated in order to modify the thermal properties by the introduction of disorder on the Co site. We show here that the thermal conductivity can indeed be reduced by such a substitution, but that this substitution predominantly induces a reduction of the electronic part of the thermal conductivity...
ABSTRACT BaTiO3-CoFe2O4 nanocomposites with a 1/1 molar ratio were prepared by a combination of p... more ABSTRACT BaTiO3-CoFe2O4 nanocomposites with a 1/1 molar ratio were prepared by a combination of polyol synthesis (chimie douce) and a subsequent consolidation by spark plasma sintering. The nanocomposite samples, with a grain size about 50 nm showed a good mixing and a high density. Their impedance response was measured in the 5 Hz-1 MHz frequency range, under magnetic fields up to 1200 kA/m. Measurements were carried out in the 40-210 °C temperature range. We used the Jonscher's universal relaxation law to analyze the electric conductivity results. Significant changes in the activation energies for long range conductivity and hopping conductivity were observed both at the coercive magnetic field of the ferrite and the Curie transition of the titanate. We show that the use of impedance spectroscopy, based on a wide frequency range, provides a far larger view of electric phenomena allowing a separation of the several contributions to the conductivity phenomena, as a function of the magnetic field.
The wealth of properties in functional materials at the nanoscale has attracted tremendous intere... more The wealth of properties in functional materials at the nanoscale has attracted tremendous interest over the last decades, spurring the development of ever more precise and ingenious characterization techniques. In ferroelectrics, for instance, scanning probe microscopy based techniques have been used in conjunction with advanced optical methods to probe the structure and properties of nanoscale domain walls, revealing complex behaviours such as chirality, electronic conduction or localised modulation of mechanical response. However, due to the different nature of the characterization methods, only limited and indirect correlation has been achieved between them, even when the same spatial areas were probed. Here, we propose a fast and unbiased analysis method for heterogeneous spatial data sets, enabling quantitative correlative multi-technique studies of functional materials. The method, based on a combination of data stacking, distortion correction, and machine learning, enables a...
There is a great interest to synthesize ferroelectric ceramics both with fine grain size and sign... more There is a great interest to synthesize ferroelectric ceramics both with fine grain size and significant electric properties. Here, we report the preparation of nanostructured tetragonal barium titanate by combining forced hydrolysis of metallic salts in polyol, soft annealing and 650 C spark plasma sintering under uniaxial pressure of 120 MPa for 5 min. The stabilization of highly dense (density of 90%), nanostructured (grains about 50 nm) tetragonal barium titanate ceramic was achieved. The produced ceramic exhibited ferroelectric behavior and a dielectric permittivity of 3600 at 1 kHz and room temperature.
Journal of Spintronics and Magnetic Nanomaterials, 2012
ABSTRACT We report on the synthesis, consolidation, magnetic properties and electrical conductivi... more ABSTRACT We report on the synthesis, consolidation, magnetic properties and electrical conductivity of cobalt ferrite-barium titanate nanostructured ceramics. The precursor oxides were separately synthesized as nanoparticles by the polyol method, namely forced hydrolysis of metallic salts in a polyol solvent, mixed and consolidated by spark plasma sintering at 500 °C for 5 min, limiting grain growth under 100 nm. Hysteresis loops showed evidence of a good mixing as an increase in coercive field as compared to isolated ferrite prepared under the same conditions. Electrical conductivity analyzed on the basis of the Jonscher Universal Law exhibited evidence of phase coupling as the onset of activation energy for hopping conductivity frequency showed a change of slope at the barium titanate transition temperature.
ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by th... more ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase.
We report the synthesis of yttrium iron garnet (YIG) combining soft chemistry route, namely the p... more We report the synthesis of yttrium iron garnet (YIG) combining soft chemistry route, namely the polyol process, and spark plasma sintering (SPS) technique. The polyol process produced an intermediary amorphous phase containing both iron and yttrium cations in the desired ratio. They were annealed at 400°C in air to decompose the organic content of the reaction (polyol and acetate). To achieve the garnet phase, the polyol-obtained precursor was subjected to reactive SPS treatment at a temperature of 750°C, far below the typical temperatures (1350°C) used in the classic solid-state reaction process. In 15 min pure and high-density Y 3 Fe 5 O 12 ceramic, with about 100 nm sized crystalline grains, was obtained. We report as well the characterization of the initial amorphous phase and the obtained YIG by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, 57 Fe M€ ossbauer spectrometry, and magnetization measurements.
ABSTRACT Multiferroic systems formed by a mixing of a ferroelectric phase and a ferrimagnetic pha... more ABSTRACT Multiferroic systems formed by a mixing of a ferroelectric phase and a ferrimagnetic phase are receiving significant attention because of their wide possibilities for tailoring properties. In this work, the magnetic properties of the cobalt ferrite-barium titanate system were investigated on samples prepared by an original combination of synthesis methods. Cobalt ferrite and barium titanate nanoparticles were synthesized separately by hydrolysis of the metal acetates in a polyol method. Both materials were mixed in a 1:1 ratio and consolidated by spark plasma sintering at 500 °C for 5 min. A high density nanostructured ceramic was obtained with grains smaller than 100 nm and a density about 80% of the theoretical value. Magnetic hysteresis loops showed a hard magnet behavior, with a coercive field larger than cobalt ferrite alone prepared under the same conditions. δM reversible magnetization plots exhibited dipolar interactions with a maximum at the coercive field. These results are interpreted in terms of an efficient mixing of the components, which strongly decreases the magnetic percolation in the composite by separating ferrite grains by titanate grains.
ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by th... more ABSTRACT Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase.
Nanostructured Materials, Edited by Mohindar Seehra, 2017
Ferrites are a well-known class of ferrimagnetic materials. In the form of nanoparticles (NPs), t... more Ferrites are a well-known class of ferrimagnetic materials. In the form of nanoparticles (NPs), they exhibit novel and fascinating properties, leading to an extremely wide variety of applications in electronics, biomedical and environmental fields. These applications result from nanoscale effects on physical properties, particularly magnetic properties. For applications in electronic devices, however, a high-density, consolidated body, with very fine grains is needed, in order to retain the nanoscale properties. To our knowledge, spark plasma sintering (SPS) is the only method permitting a full densification with final grain size in the nanometer range. In this review, we examine the SPS method as applied to ferrites and, in particular, the effects of SPS parameters on the final nanostructures obtained. Due to their technological impact, we also discuss the SPS fabrication of hybrid multiferroic nanostructures composed of a ferrite and a ferroelectric phase.
Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol
... more Ferrite magnetic nanoparticles in the composition Zn0.7Ni0.3Fe2O4 were synthesized by the polyol method, with an average size of 8 nm. Electron spin resonance (ESR) measurements were carried out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase
Uploads
Papers by Ulises Acevedo Salas
method, with an average size of 8 nm. Electron spin resonance (ESR) measurements were carried
out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase
method, with an average size of 8 nm. Electron spin resonance (ESR) measurements were carried
out at a frequency of 9.45 GHz in the 100–500K temperature range. Obtained results exhibited a characteristic ESR signal in terms of resonance field, Hres, linewidth, DH, and peak ratio, R, for each magnetic phase. At low temperatures, the ferrimagnetic phase showed low Hres, broad DH, and asymmetric R. At high temperatures, these parameters exhibited opposite values: high Hres, small DH, and R1. For intermediate temperatures, a different phase was observed, which was identified as a superparamagnetic phase by means of zero-field cooling-field cooling and hysteresis loops measurements. The observed differences were explained in terms of the internal fields and especially due to the cubic anisotropy in the ordered phase