Toward miniaturized undulators with L1${}_0$ phase FePt micromagnet array

An undulator is a required part for building free-electron lasers (FELs) upon which a large body of the literature has expressed interest for the applications in various areas such as the defense industry, material science, and medicine. The current state of the art of X-FEL uses an undulator period down to 3 cm, which creates an output radiation wavelength down to 1.5 A using ≈14 GeV e-beam. By developing a mm/sub-mm period undulator (i.e., a period of 300 µm), it is possible to obtain the same output radiation wavelength with a much less e-beam energy of ≈1.4 GeV. Thus, compact XFELs could become a reality. In this work, FePt thin films and micromagnets are synthesized by the sputtering deposition technique, and their properties are studied. The X-ray diffraction (XRD) pattern indicated that the crystal structure transformed from face-centered cubic (FCC) to L1${}_0$ face-centered tetragonal (FCT) phase upon annealing. Room temperature coercivity of the structures reached up to 1.4 Tesla. Undulator prototype is developed and the performance tests are done using Genesis simulation. Simulations yield output radiation with 0.52 nm wavelength and 0.7 GW peak power. Synthesized FePt micromagnets could be utilized in next-generation miniaturized undulators. (© 2022 Wiley‐VCH GmbH)