Nikon D7200 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Expeed 4 processor. On the other hand, Samsung NX300M has a
20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features DRIMe IV processor.
Another difference between these two cameras is that Nikon D7200's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the D7200 and NX300M sensor size comparison.
Nikon D7200 and Samsung NX300M have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.