  A SrRuO$_3$ (SRO) thin film and its heterostructure have brought much
attention because of the recently demonstrated fascinating properties, such as
topological Hall effect and skyrmions. Critical to the understanding of those
SRO properties is the study of the spin configuration. Here, we conduct
resonant soft x-ray scattering (RSXS) at oxygen K-edge to investigate the spin
configuration of a 4 unit-cell SRO film that was grown epitaxially on a single
crystal SrTiO$_3$. The RSXS signal under a magnetic field (~0.4 Tesla) clearly
shows a magnetic dichroism pattern around the specular reflection. Model
calculations on the RSXS signal demonstrate that the magnetic dichroism pattern
originates from a N\'eel-type chiral spin structure in this SRO thin film. We
believe that the observed spin structure of the SRO system is a critical piece
of information for understanding its intriguing magnetic and transport
properties.
