At some point in their early history (after the year 5000, during the Great War) the Daleks were developing an experimental magnetron to use as a weapon. A huge circular coil, it would be capable of producing powerful magnetic fields through superconductivity and be able to draw passing starships out of the sky. (PROSE: The Evil of the Daleks)
The Time Lords used a magnetron to transport the entire solar system in what became known as the Ravolox affair. (TV: The Mysterious Planet, The Ultimate Foe) The Magnetron was later used to return the solar system to its original location. (PROSE: The Eight Doctors)
The Daleks used a magnetron to move 27 planetary bodies to the Medusa Cascade. The Tenth Doctor, the Meta-Crisis Tenth Doctor and Donna Noble later used it to return all but one of them to their original locations. (TV: Journey's End)
The Daleks' version was evidently somewhat more advanced than the Time Lord version, which destroyed most of Earth's surface when it was used on the planet; by comparison, the Dalek version did no apparent damage at all to the planet, however it was used to move the rest of the solar system at the same time so it must have caused some feedback. While it can be assumed that the Time Lord magnetron probably could have been used to transport objects through time as well as space, only the Dalek technology was explicitly shown to have a temporal aspect, as some of the stolen planets were taken from completely different moments in time. (TV: Journey's End)
Alternate timelines Edit
In an alternate timeline, the Daleks used a time vortex magnetron which would cause the human guerrillas who had travelled to the 20th century to be drawn to the Daleks' base the next time they used their time machine. By mistake, Jo Grant was drawn in instead. (TV: Day of the Daleks)
Behind the scenes Edit
Magnetrons are real-life devices, from which their use in Doctor Who can be reasonably extrapolated. They are used in the transmission of television signals and are the source of power in microwave ovens. They allow for the quick production of a great deal of energy.