The thermal evolution of FePt thin film under plasma focus pulsed ion irradiation

Summary form only given. Energetic single shot H⁺ ion irradiation in dense plasma focus device (DPF) has been proved as an effective method for modification of pulsed laser deposition (PLD) synthesized FePt thin films. In our experiment, a UNU/ICTP dense plasma focus device was employed for pulsed ion irradiation with the charging voltage of 14 kV and storage energy of 2.94 kJ. FePt thin films were irradiated at a distance of 4 cm with the filling hydrogen gas pressure of 5 mbar and the ion energy ranges from 35 keV to 1.5 MeV measured by Faraday Cup. Since the pulsed nature and the energy spectrum of the ion beams differ from the standard continuous ion irradiation process, after single shot H⁺ ion irradiation, FePt nanoparticles have successfully achieved and phase transition temperature from magnetically soft fcc to magnetically hard fct phase has been lowered down to 400 degC with enhanced magnetic properties. These results are due to thermal effect in a transient melting and rapid quenching process induced by a pulsed fast and energetic H⁺ ion irradiation. Therefore, a better understanding of this transient thermal effect is necessary to fully understand the effect of plasma focus ion beam on the irradiated surface. In this paper, the thermal evolution of the irradiated surface is studied using numerical simulation calculation with respect to the geometry and physical characteristics of the ion beams, the ion beam-thin film interaction process and the thermal properties of the FePt thin films. The simulation is based on the computation of the temperature distribution in the ion irradiated FePt thin films. The numerical results are made for better understanding of ion irradiation effects for FePt thin films.