Static and dynamic compression of metals probed by synchrotron radiation

Orateur : Raffaella TORCHIO (CEA Ile de France)

In this talk I will present the research I carried out during my PhD thesis at ESRF and my postdoc at CEA, Ile de France. The first part concerns the study of structural and magnetic transformations that occur in the transition metals (Fe, Co and Ni) submitted to extreme pressures in a diamond anvil cell. The investigation has been carried out using polarized X-ray absorption (X-ray magnetic circular dichroism or XMCD) coupled to X-ray diffraction and DTF calculations and applied to the cases of cobalt, nickel and iron-cobalt (FeCo) alloys. In particular, in cobalt the first experimental evidence of pressure-induced suppression of ferromagnetism is shown together with an insight into the interplay between structural and magnetic changes. The case of nickel, structurally stable over a wide range of pressures, allowed to go deeper into the interpretation of the K-edge XMCD signal, so far still unsettled. Finally the investigation of the FeCo alloys was aimed at understanding the role played by the chemical order in tuning the high pressure structural and magnetic properties. The second part concerns the development of new approaches to the investigation of the microscopic properties of metals under dynamic conditions by means of synchrotron radiation, in particular regarding the conception of laser shock experiments to be probed by time resolved spectroscopy and diffraction. Dynamic compression in the nanosecond range is interesting not only since it allows exploring “exotic” states of matter like the Warm Dense Matter, but also as it can bring complementary information to the static studies. Laser-shock experiment using KJoule lasers are nowadays quite widely used to achieve the Mbar pressures, however such experiments are very costly and difficult to access. Our alternative strategy is to bring or built a compact but powerful laser (pump) to a synchrotron facility (probe) – namely ESRF – somehow retracing the path of static compression which brought to the successful coupling of the diamond anvil cell to synchrotron techniques. First attempts on the time resolved XRD beamline ID09b and future experiments on the time resolved absorption beamline ID24 will be presented.

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