The core of a conventional Mössbauer spectrometer consists of an electromagnetic driver to move t... more The core of a conventional Mössbauer spectrometer consists of an electromagnetic driver to move the radioactive source, and a proportional gas counter, both components must be at ambient conditions. At present, special cryostat designs must be used for that purpose, increasing the cost and volume of the Mössbauer system. We have improved the conventional design by introducing a multilayer piezoelectric driver and a Si solid-state detector in place of the conventional elements. The piezoelectric driver can work at high frequencies (0.1-2 kHz) and the new set up can be assembled in a very compact way (a cylinder of approximate 15 cm length and 2 cm diameter). This new design broadens the capabilities of Mössbauer spectroscopy by allowing the spectrometer to be inserted into a conventional low-temperature and high-magnetic field cryostat. We have already built two prototypes that work in different frequency ranges.
Magnetic properties of CoFe2O4 particles were investigated by means of zero-field and in-field Mö... more Magnetic properties of CoFe2O4 particles were investigated by means of zero-field and in-field Mössbauer spectrometry. The studies include superparamagnetic (SP) relaxation as well as the surface phenomena of samples with different particle sizes both in the form of ferrofluids and powders. A core-shell model was applied to estimate the thickness of the surface ``spin-canted'' shell around particles.
The production and structural characterization of gas-evaporated nanoparticles in the Fe1−xCrx sy... more The production and structural characterization of gas-evaporated nanoparticles in the Fe1−xCrx system, with 0<x<0.83 are reported. The results show that for x∼0.5 the metastable σ-FeCr can be stabilized and it constitutes up 60wt% of the material. The sample with the highest σ-FeCr content is further analyzed to study the structural and the magnetic properties of this phase and its thermal stability. The σ-FeCr phase is weakly magnetic with an average magnetic moment of 0.1μB per Fe atom and a Curie temperature below ∼60K. It is stable up to 550K where it starts to transform to bcc-FeCr. Annealing at 700K yields Cr2O3 due to Cr surface segregation and affects the magnetic behavior of the system, which is dominated by interparticle interactions.
We report the results of magnetization and Fe57 Mössbauer spectroscopy measurements performed in ... more We report the results of magnetization and Fe57 Mössbauer spectroscopy measurements performed in the temperature range 5–300 K on composites containing iron–oxide nanoparticles encased in polystyrene type resins. After carrying out a suitable field treatment in order to decouple the particles from the matrix, a fraction of the particles freely rotate in response to an applied magnetic field.
Magnetic silica-aerogel composites have been synthesized by dispersing hard magnetic Nd2Fe14B par... more Magnetic silica-aerogel composites have been synthesized by dispersing hard magnetic Nd2Fe14B particles in a sol during a fast sol-gel process and subsequently supercritically drying the resulting gels. The composites are found to retain most of the outstanding properties of their constituents: the large coercivity and moderate remanence of the magnetic powders and the transparency and low density of silica aerogels. Moreover, aerogels synthesized in the presence of a magnetic field exhibit the alignment of the particles, forming needle-like structures along the direction of the applied magnetic field, which results in optical and magnetic anisotropies. Due to their unique combination of properties, these types of materials may be appealing for magneto-optics and magnetic actuator applications.
This paper provides a detailed technological characterization of the Roman opus sectile glasses (... more This paper provides a detailed technological characterization of the Roman opus sectile glasses (second century AD) coming from the renowned Gorga collection. Nine glass samples corresponding to imitations of the porfido verde antico, cipollino rosso, rosso antico, giallo antico, diaspro nero e giallo, semesanto and agate/alabaster stones were studied. The aim of this study was twofold: (i) archaeometric, i.e., to provide valuable data on the production, raw materials and techniques of these refined Roman glasses that mimic precious stones and (ii) methodological, i.e., to highlight the good performance of combining polished thin sections and local probe measurements for the study of glassy microstructures. Based on the nature of the flux used, the glasses from the samples were classified as either natron-type or mixed-type (natron/plant ash). The latter stem from remelted glasses and contain relict grains of wollastonite that were not found in the pure natron samples. Relict wollas...
The core of a conventional Mössbauer spectrometer consists of an electromagnetic driver to move t... more The core of a conventional Mössbauer spectrometer consists of an electromagnetic driver to move the radioactive source, and a proportional gas counter, both components must be at ambient conditions. At present, special cryostat designs must be used for that purpose, increasing the cost and volume of the Mössbauer system. We have improved the conventional design by introducing a multilayer piezoelectric driver and a Si solid-state detector in place of the conventional elements. The piezoelectric driver can work at high frequencies (0.1-2 kHz) and the new set up can be assembled in a very compact way (a cylinder of approximate 15 cm length and 2 cm diameter). This new design broadens the capabilities of Mössbauer spectroscopy by allowing the spectrometer to be inserted into a conventional low-temperature and high-magnetic field cryostat. We have already built two prototypes that work in different frequency ranges.
Magnetic properties of CoFe2O4 particles were investigated by means of zero-field and in-field Mö... more Magnetic properties of CoFe2O4 particles were investigated by means of zero-field and in-field Mössbauer spectrometry. The studies include superparamagnetic (SP) relaxation as well as the surface phenomena of samples with different particle sizes both in the form of ferrofluids and powders. A core-shell model was applied to estimate the thickness of the surface ``spin-canted'' shell around particles.
The production and structural characterization of gas-evaporated nanoparticles in the Fe1−xCrx sy... more The production and structural characterization of gas-evaporated nanoparticles in the Fe1−xCrx system, with 0<x<0.83 are reported. The results show that for x∼0.5 the metastable σ-FeCr can be stabilized and it constitutes up 60wt% of the material. The sample with the highest σ-FeCr content is further analyzed to study the structural and the magnetic properties of this phase and its thermal stability. The σ-FeCr phase is weakly magnetic with an average magnetic moment of 0.1μB per Fe atom and a Curie temperature below ∼60K. It is stable up to 550K where it starts to transform to bcc-FeCr. Annealing at 700K yields Cr2O3 due to Cr surface segregation and affects the magnetic behavior of the system, which is dominated by interparticle interactions.
We report the results of magnetization and Fe57 Mössbauer spectroscopy measurements performed in ... more We report the results of magnetization and Fe57 Mössbauer spectroscopy measurements performed in the temperature range 5–300 K on composites containing iron–oxide nanoparticles encased in polystyrene type resins. After carrying out a suitable field treatment in order to decouple the particles from the matrix, a fraction of the particles freely rotate in response to an applied magnetic field.
Magnetic silica-aerogel composites have been synthesized by dispersing hard magnetic Nd2Fe14B par... more Magnetic silica-aerogel composites have been synthesized by dispersing hard magnetic Nd2Fe14B particles in a sol during a fast sol-gel process and subsequently supercritically drying the resulting gels. The composites are found to retain most of the outstanding properties of their constituents: the large coercivity and moderate remanence of the magnetic powders and the transparency and low density of silica aerogels. Moreover, aerogels synthesized in the presence of a magnetic field exhibit the alignment of the particles, forming needle-like structures along the direction of the applied magnetic field, which results in optical and magnetic anisotropies. Due to their unique combination of properties, these types of materials may be appealing for magneto-optics and magnetic actuator applications.
This paper provides a detailed technological characterization of the Roman opus sectile glasses (... more This paper provides a detailed technological characterization of the Roman opus sectile glasses (second century AD) coming from the renowned Gorga collection. Nine glass samples corresponding to imitations of the porfido verde antico, cipollino rosso, rosso antico, giallo antico, diaspro nero e giallo, semesanto and agate/alabaster stones were studied. The aim of this study was twofold: (i) archaeometric, i.e., to provide valuable data on the production, raw materials and techniques of these refined Roman glasses that mimic precious stones and (ii) methodological, i.e., to highlight the good performance of combining polished thin sections and local probe measurements for the study of glassy microstructures. Based on the nature of the flux used, the glasses from the samples were classified as either natron-type or mixed-type (natron/plant ash). The latter stem from remelted glasses and contain relict grains of wollastonite that were not found in the pure natron samples. Relict wollas...
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