A method is for depositing a dielectric material on to a substrate in a chamber by pulsed DC magnetron sputtering with a pulsed DC magnetron device which produces one or more primary magnetic fields. In the method, a sputtering material is sputtered from a target, wherein the target and the substrate are separated by a gap in the range 2.5 to 10 cm and a secondary magnetic field is produced within the chamber which causes a plasma produced by the pulsed DC magnetron device to expand towards one or more walls of the chamber.