Magnetic Barkhausen noise measurement by resonant coil method

This paper describes a powerful new technique for nondestructive evaluation of ferromagnetic material. A method has been developed for measuring magnetic Barkhausen signals under different coil resonance frequencies. The measurements allow one to establish the behavior relating the power spectral density maximum and the resonant coil frequency. Time-frequency analysis of Barkhausen signals puts in evidence the tuning regions for each coil, and allows clear identification of each contribution to the Barkhausen signal spectrum. This concept was used in order to evaluate the relation between the degree of plastic deformation in carbon steel samples, and the power spectral density maximum at different resonance frequencies. This result also makes it possible to the selectively modify measurement sensibility to the magnetic Barkhausen signal by using different resonance frequencies.     

SIMS studies of polymeric tertiary structures in monolayers: Polysiloxane helical coil structures

A static SIMS study was performed using poly(dimethyl siloxane) (PDMS) as a model system to investigate the effects of tertiary structure on the ion formation mechanism and ion formation probability of fragments in the high mass region (>1000 Da). PDMS produced from anionic polymerization with a narrow polydispersity, can form well-ordered helically coiled monolayers using Langmuir-Blodgett methods at the air water interface, either in a hairpin configuration, if the endgroups are functional or as flat helically coiled chains. Reflection absorption Fourier transform infrared (RA-FTIR) spectroscopic analysis shows the changes in bonding between flat helically coiled PDMS and cast films from dilute solvents, which produces a random coil configuration. Differences between the model systems in infrared spectrum show evidence of changes in structure, producing variation in band formation. Also observed are changes in the band shape and relative peak area between the model systems. These polymeric changes translate into differences in the relative intensities of fragments formed in the repeating pattern of clusters in the high mass ToF-SIMS spectra of the ordered versus the random cast films. Both statistical chain break analysis and molecular mechanics simulations of structure are used to support the analysis.     

Magnetic structures and neutron polarimetry

In a thermal neutron scattering experiment, Spherical Neutron Polarimetry (SNP) requires that the incident and the final neutron polarization vectors be measured independently. The method exploits the maximum information one can get from magnetic neutron scattering. Recently, it has been used quite successfully in the study of antiferromagnetic structures and their domain populations. The challenging measurement is now straightforward with our neutron polarimeter CRYOPAD as long as the sample chamber does not contain any magnetic field. Polarimetry on magnetized samples remains the domain of the classical Uniax ial Polarization Analysis (UPA) which measures only the longitudinal component of polarization in an applied field.     

Magnetic disaccommodation in normal spinel structures

Magnetic disaccommodation is investigated for ferrous ferrites with normal spinel structure. This study shows the presence of a new relaxation process in the temperature region IV (285 K) that has not been detected in inverse spinels. A numerical analysis of the isochronal spectra reveals that it is composed of two simple Debye processes with activation energies close to 0.75 eV and 0.80 eV, and preexponential factors 3×10^–13 s. This relaxation is attributed to the formation of an induced anisotropy due to jumps of B-Fe ions into vacancies (as process III), but in presence of a divalent cation occupying an A-site.