Synthesis, structural and magnetic characterization of lead-metaniobate/cobalt-ferrite nanocomposite films deposited by pulsed laser ablation

Detailed structural, microstructural and magnetic measurements were performed on (PbNb2O6)(1-x) -(CoFe2O4) (x) nanocomposite thin films deposited by laser ablation on Si(001)\Pt substrates, with different cobalt ferrite concentrations. The tuning of the lead concentration, due to the lead volatility, was found to be particularly important in order to obtain the orthorhombic (ferroelectric) lead niobate phase. The lattice parameter of CoFe2O4 was below the bulk value, indicating the presence of compressive strains on this phase. A magnetic anisotropy was observed, which favored the orientation of the magnetization in the direction perpendicular to the plane of the films, for cobalt ferrite concentrations 40-50 %. The shape, stress and magnetocrystalline anisotropy fields on the composites were calculated and compared. It was found that the perpendicular magnetic anisotropy was induced by the presence of strain on the ferrite phase in the films.- This work has been supported by Fundacao para a Ciencia e Tecnologia (FCT) and FEDER, through the projects POCI/CTM/60181/2004 and PTDC/CTM/099415/2008. J. Barbosa and I. T. Gomes gratefully acknowledge Ph.D. grants from Fundacao para a Ciencia e Tecnologia (SFRH/BD/41913/2007 and SFRH/BD/36348/2007, respectively).info:eu-repo/semantics/publishedVersio

Non-linearity in photothermal radiometric imaging

Non-linear effects occurring in photothermal microscopes based on principle of photothermal radiometry are studied as a function of the laser power and of the modulation frequency. For stainless steel, a second harmonic component of up to 11 % of the fundamental amplitude is found. Phase shifts of up to 20 degrees are observed as a function of the modulation frequency. The nonlinearity is mainly due to Stefan-Boltzmann's law. The experimental results are in good agreement with a theoretical model based on the static and oscillating temperature distribution

Non-linearity in photothermal radiometric imaging

Non-linear effects occurring in photothermal microscopes based on principle of photothermal radiometry are studied as a function of the laser power and of the modulation frequency. For stainless steel, a second harmonic component of up to 11 % of the fundamental amplitude is found. Phase shifts of up to 20 degrees are observed as a function of the modulation frequency. The nonlinearity is mainly due to Stefan-Boltzmann's law. The experimental results are in good agreement with a theoretical model based on the static and oscillating temperature distribution

Flying-spot lock-in thermography and its application to thickness measurement and crack detection

Abstract A heating laser beam was scanned periodically along a testing path on the surface of a test object. The thermal response of the beam was recorded by an infrared camera. Using a lock-in thermography algorithm, amplitude and phase images were generated. The phase image is corrected for effects due to the beam movement. A first application shows the contact-free determination of the steel sheet thickness at forming edges. Calibration of phase values to thickness was achieved by using an analytical model of thermal wave transmission. A second application is the detection of a perpendicular surface crack in steel

Nondestructive testing of ceramic-metal joints by high-frequency ultrasound techniques

A high-frequency ultrasound system for the frequency range 10-200 MHz is used to characterize the homogeneity of cermic-metal joints nondestructively by C-and B-scanning. Alumina-aluminium joints produced by friction welding, eutectic AlN-copper joints, an alumina substrate for electronics with striplines and an alumina steel foint for dental surgery have been tested. Various inhomogeneities have been found for all examples

Moderne Thermographie-Verfahren - Impuls- und Lock-In-Thermographie

The basics of pulsed thermography and lock-in thermography are presented. Both variants of dynamic active thermography are assessed in comparison with respect to their advantages and application fields

Imaging of magnetic surfaces by detection of photothermally modulated stray fields

Images from surfaces of ferro- and ferrimagnetic solids are obtained by photothermal modulation of magnetic properties by a focused laser beam and by measuring the surface stray fields using a sensor coil. The lateral resolution is about 10 µm. The method was applied to a sample consisting of cementite plates in an austenite matrix and to monocrystalline ferrite material for video recording heads. Amplitude and phase images are influenced strongly by external magnetic fields. The signal is increasing slightly as a function of the modulation frequency

Ultraschallsensoren

Ultrasound sensors for non-destructive testing allow to obtain acoustical images from the depth of the test object. Using high-frequency ultrasound at 50-100 MHz, delaminations in microchips are detected. Real-time detection of defects is feasible with the scanning laser acoustic microscope. Synthetic aperture techniques help to improve contrast and lateral resolution of the image. Contact-free ultrasound testing is feasible by air-coupled transducers

Mikrothermographie als Werkzeug zur Prüfung von Klebeverbindungen

Mit Hilfe des Wärmemikroskopes ALADIN wurde die flächige Verklebung eines dünnen Bleches berührungsfrei geprüft. Die Klebestoffverteilung unter dem Blech kann in verschiedenen Stadie während des Aushärtevorganges sichtbar gemacht werden