In one embodiment a system to detect multi-domain regions in the soft under layer of a perpendicular magnetic media comprises a radiation targeting assembly to target a polarized radiation beam onto a surface of a substrate covered by the soft under layer of a perpendicular magnetic media, a radiation collecting assembly that collects radiation reflected from the surface, a processor coupled to the first radiation collecting assembly, and a memory module coupled to the processor. The memory module comprises logic instructions which, when executed by the processor, configure the processor to record signal values from radiation reflected by the radiation beam at different positions on the surface and analyze the signal values to detect a region of multiple magnetic domains in the soft under layer of a perpendicular magnetic media.