  Presence of multiple competing periodicities may result in a system to go
through states with modulated periodicities, an example of which is the
self-similar staircase-like structure called the Devil's staircase. Herein we
report on a novel staircase structure of domain periodicity in an amorphous and
achiral Fe/Gd magnetic thin film wherein the reciprocal space wavevector
\textbf{Q} due to the ordered stripe domains does not evolve continuously,
rather exhibits a staircase structure. Resonant X-ray scattering experiments
show jumps in the periodicity of the stripe domains as a function of an
external magnetic field. When resolved in components, the step change along
Q$_x$ was found to be an integral multiple of a minimum step height of 7 nm,
which resembles closely to the exchange length of the system. Modeling the
magnetic texture in the Fe/Gd thin film as an achiral spin arrangement, we have
been able to reproduce the steps in the magnetization using a Landau-Lifshitz
spin dynamics calculation. Our results indicate that anisotropy and not the
dipolar interaction is the dominant cause for the staircase pattern, thereby
revealing the effect of achiral magnetism.
