Epitaxial Co/Pt films have been deposited by dc-magnetron sputtering onto heated C-plane sapphire substrates. X-ray diffraction, the residual resistivity and transmission electron microscopy indicate that the Co/Pt films are highly ordered on the atomic scale. The coercive field and the perpendicular magnetic anisotropy increase as the substrate temperature is increased from 100-250C during deposition of the Co/Pt. Measurement of the domain wall creep velocity as a function of applied magnetic field yields the domain wall pinning energy, which scales with the coercive field. Evidence for an enhanced creep velocity in highly ordered epitaxial Co/Pt is found. 2Co/Pt multilayers have been studied for a number of years 1,2 , initially because of their potential as magneto-optical recording media 3 . Their attractive properties include perpendicular magnetic anisotropy (PMA) and a large polar magneto-optic Kerr effect (MOKE) at short wavelengths 4 . More recently Co/Pt has become an interesting system for the study of the physics of domain walls (DWs) [5][6][7][8] , and spin torque [9][10][11][12][13] . The PMA leads to the formation of narrow, nanometre-scale DWs, and the large polar Kerr effect is convenient for measuring the DW motion. However, DWs tend to pin at grain boundaries in the polycrystalline Co/Pt that is typically used in these studies 9 , and this is an issue not only for investigations of the fundamental physics of DWs but also for future devices which may depend upon reliable DW motion, such as racetrack memory 14 . Epitaxial Co/Pt, in which the density of grain boundaries is minimised, could provide a solution to this problem. Ideally, however, the method of multilayer deposition should be compliant with industrial processes.Sputtering is a convenient, cost-effective technique for thin film deposition and may be used to grow films epitaxially if a single crystal substrate is heated to an appropriate temperature.In order to obtain PMA in epitaxial Co/Pt, the films are required to grow in the (111)-orientation 15 , and (111) texture was first seen in sputtered Co/Pt in 1993 16 . While there have been studies of Co/Pt superlattices 17 and Pt/Co/Pt sandwiches 18 grown by sputtering, there has been no optimisation of sputtered epitaxial Co/Pt (111) for DW devices. Here we show how the substrate temperature may be used to tune the magnetic properties of epitaxial Co/Pt grown on sapphire.First, the growth of Pt on C-plane (0001) sapphire was optimised. A 60 nm Pt film was deposited at various substrate temperatures in the range 400-700C. High angle X-ray scans all had a clear peak between 39.5 and 40, indicating (111) structure (see Figure 1). The 3 peak was largest and the satellite peaks were best defined for a deposition temperature of 500C indicating that at this temperature the crystal quality of the film was highest. It was also found that overnight annealing of the sapphire substrate at 700 C improved film quality. X-ray reflectivity curves were measured from Pt films deposited both after a s...