We demonstrate the current induced effective magnetic field via spin Hall effect in perpendicularly magnetized Pt (6 % x nm)/Co/Pt (x nm) (x = 1, 2, 3) films. Measurements were carried out by an AC magnetization tilting technique. The relation between the spin Hall effective field and the degree of asymmetry of the top and bottom Pt layer thicknesses was determined. It is found that the spin Hall field is the largest in the film with Pt5nm/Co/Pt1nm, with the most asymmetric Pt layer thickness. This result is consistent with a net spin Hall torque arising from the bottom Pt layer unimpeded by the opposite spin Hall torque from the top Pt layer suppressed by spin diffusion. A spin Hall field of 267Oecm2/108A was achieved in the Pt5nm/Co/Pt1nm structure.