  Single x-ray photons can be resonantly scattered and stored with the help of
suitable transitions in the atomic nucleus. Here, we investigate theoretically
means of mechanical-free modulation for the frequency spectra of such x-ray
photons via periodic switching of an external magnetic field. We show that
periodically switching on and off an external magnetic field generating
hyperfine splitting of the nuclear transition leads to the generation of
equidistant narrow sidebands of the resonantly scattered response. This
frequency-comb-like structure depends on the magnitude and orientation of the
applied magnetic field and on the switching period. An analytical approach for
the characterization of the comblike frequency spectrum is presented. The
feasibility of the external control on the frequency modulation of the x-ray
response is discussed in view of possible applications in high-resolution
spectroscopy or quantum technology.
