Phase transition in nanomagnetite

Recently, the application of nanosized magnetite particles became an area of growing interest for their potential practical applications. Nanosized magnetite samples of 36 and 9 nm sizes were synthesized. Special care was taken on the right stoichiometry of the magnetite particles. Mössbauer spectroscopy measurements were made in 4.2–300 K temperature range. The temperature dependence of the intensities of the spectral components indicated size dependent transition taking place in a broad temperature range. For nanosized samples, the hyperfine interaction values and their relative intensities changed above the Verwey transition temperature value of bulk megnetite. The continuous transition indicated the formation of dendritelike granular assemblies formed during the preparation of the samples

Practical Verification of Decision-Making in Agent-Based Autonomous Systems

We present a verification methodology for analysing the decision-making component in agent-based hybrid systems. Traditionally hybrid automata have been used to both implement and verify such systems, but hybrid automata based modelling, programming and verification techniques scale poorly as the complexity of discrete decision-making increases making them unattractive in situations where complex log- ical reasoning is required. In the programming of complex systems it has, therefore, become common to separate out logical decision-making into a separate, discrete, component. However, verification techniques have failed to keep pace with this devel- opment. We are exploring agent-based logical components and have developed a model checking technique for such components which can then be composed with a sepa- rate analysis of the continuous part of the hybrid system. Among other things this allows program model checkers to be used to verify the actual implementation of the decision-making in hybrid autonomous systems

Mechanical alloying of Fe–Si and milling of α- and β-FeSi2 bulk phases

Iron disilicide synthesis by mechanical alloying was performed. ɛ-FeSi, α-Fe1−xSi2, amorphous FeSi2 were formed with relative intensities depending on the milling period. β-FeSi2 phase was formed after annealing the gridded powder at the temperature where this phase is stable. Mössbauer spectroscopy and X-ray diffraction methods were applied to determine the different phases formed. The morphology of the resulting particles was observed by high resolution scanning electron microscopy. The effect of the milling on bulk iron–silicide samples was and studied chemical effects of the ball milling on Fe–Si2 systems have been studied

Structural and magnetic characterization of Fe/Cr/Fe tri-layers and Fe/Cr multilayers after swift Au ion irradiation

International audienceFe/Cr/Fe trilayers and Fe/Cr multilayers were irradiated by 163 MeV Au ions with fluence of 1 × 1011 ions/cm2 to 50 × 1011 ions/cm2. The structural properties of Fe/Cr interfaces were observed using Conversion Electron Mössbauer Spectroscopy (CEMS) and X-ray reflectivity (XRR). The magnetic exchange coupling between Fe layers through Cr spacer in trilayers and multilayers was determined from hysteresis loops measured with SQUID magnetometer. The different behavior of Fe/Cr/Fe trilayers and Fe/Cr multilayers was observed after Au ions irradiation. In Fe/Cr multilayers a decrease of the average value of hyperfine magnetic field with increasing Au ions fluence was observed, indicating an increase of the interfacial roughness. In Fe/Cr/Fe trilayers the non-monotonic behavior of average value of hyperfine magnetic field versus ion fluence was observed suggesting the smoothing of the interfaces at small fluences and roughening at higher ones. The smoothening of interfaces was confirmed by XRR spectra. In multilayers the magnetic properties changed in a similar way as the structural properties and continuous decay of antiferromagnetic coupling as a function of fluence was observed. In trilayers at the low fluences the antiferromagnetic coupling was not sensitive on irradiation, while at large fluences the decrease of antiferromagnetic coupling fraction was seen