There is a strong demand for small foot-print high-flux hard X-rays machines in order to enable a large variety of science activities and serve a multidisciplinary user community. For this purpose, two compact Inverse Compton Sources (ICSs) are currently being developed in Italy. The most recent one is the Bright and Compact X-ray Source (BriXS) which has recently been proposed to produce very energetic X-rays (up to 180 keV) and high photon flux (up to 1013 photons/s with expected bandwidth of 1-10%). BriXS will be installed in Milan and it will enable advanced large area radiological imaging applications to be conducted with mono-chromatic X-rays, as well as allowing basic fundamental science of matter and health sciences at both pre- and clinical levels. Based on an energy-recovery linac (ERL) scheme and superconducting technology, BriXS will operate in CW regime with an unprecedented electron beam repetition rate of 100 MHz. The second Italian ICS light source is the Southern Europe Thomson back-scattering source for Applied Research (STAR) which is currently installed at the University of Calabria (UniCal). STAR is a compact machine that has been designed to produce monochromatic and tunable, ps-long, polarized X-ray beams in the range 40-140 keV with a photon flux up to 1010 photons/s and energy bandwidth below 10%. The electron beam injector is based on normal-conducting technology in S-Band with a repetition rate up to 100 Hz.
The spin dynamics triggered by an ultrashort optical excitation can lead to a variety of behaviors depending on the
specific spin and electronic structure of the material. In metallic films, electron-quasiparticles (phonons and magnons)
interactions takes place on sub-picosecond timescale and demagnetization is established within 100 fs. In half-metal
oxides, spin dynamics is much slower (100 ps) due to the inhibition of spin-flip processes. Furthermore, the dynamics of
magnetic anisotropies can be exploited to control the magnetization in ferromagnets. Optically-induced reversible
switching of the magnetization has been recently demonstrated in thin magnetic layers on the 100 picoseconds timescale.
Barkhausen noise (BN) is a prototypical example of a complex system where the probability distributions for most relevant quantities follow a power-law behavior. In our experiment we investigated the role of temperature in determining the statistical properties of BN in thin Fe films. In the temperature range between 10 K and 295 K the probability distribution for the amplitude of the magnetization avalanches is always a power-law. The critical exponent a, however, undergoes a strong variation since its value changes from α = 1 at 295 K to α = 1.8 at 10 K. At our knowledge this is the first experimental evidence of the role of temperature in BN and, more generally, in complex systems. The experimental results are discussed in terms of a generalized version of the energy equipartition principle. Within this ansatz, the energy released during the dynamical evolution of the system is "shared" between all the available avalanches, depending on their size. Avalanches of a given size constitute a "mode" of evolution of the system: the energy globally released during the magnetization process is equally shared between all the available modes. In our experiment this behavior is actually observed at room temperature. At low temperature a "freezing" of the system prevents the occurrence of large size events and therefore energy is mostly released through jumps with small amplitude.