We report on the interplay between surface morphology and the magnetic properties of Pt/Mn ultra-thin bilayers by measuring the temperature dependence of the resistivity of Hall bars cooled under application of an external magnetic field. The resistivity (ρ) versus temperature (T) curves measured under a magnetic field applied along the x-, y- and z- directions exhibit a clear difference between the zero-field-cooled (ZFC) and field-cooled (FC) traces. The disparity between the ZFC and FC traces allowed us to determine the direction of the magnetic easy-axis. The ρ vs. T characteristic of the Pt/Mn bilayers revealed the existence of antiferromagnetic (AF) order below 79 K, in agreement with the Néel temperature observed in temperature dependent susceptibility curves. We also investigated the morphological evolution of the Mn films as a function of Mn thickness by atomic force microscopy (AFM). We observed the formation of a Mn layered structure on a 2nm-thick Al2O3 buffer layer for films thicker than 2.5 nm. Our results suggest that bilayer structures consisting of non-magnetic noble metals on ultra-thin antiferromagnetic metals can be used as a probe to explore the complex magnetic properties of the AF layer.