Local M-H loops have been measured on the free layer of a magnetic tunnelling junction using a magneto-optical Kerr effect system, with 2-μm spatial resolution, to investigate the distribution of the interlayer exchange-coupling field (HE) and the coercivity (Hc) on the free layer. HE and Hc increase gradually from a junction edge, reach a maximum at the centre and then fall off gradually at the other edge. Annealing enhances HE and smooths it out at the junction centre but Hc decreases after annealing. Two-dimensional plots of HE and Hc show symmetric saddle shapes with their axes aligned with the pinned layer due to the shadow-mask effect during deposition. HE measured along the pinned layer in this case shows a ridge curve with peaks at junction edges but Hc is nearly constant. Atomic force microscopy measurements show that the roughness variations over the junction are similar to HE with greater roughness at the centre, indicating mutual correlation and confirming the origin of HE to be Néel's orange-peel coupling based on surface roughness.