Maglev trains stop by reversing the direction of the magnetic fields that normally propel them forward. As with the initial propulsion, this is accomplished without any physical contact with the rails. The entire system uses electromagnets or superconducting magnets to create a type of linear motor that controls the motion of the train.
There are many advantages to Maglev trains over traditional trains where metal wheels are in contact with metal rails. The fact that Maglev trains are floated on magnetic fields away from any physical contact with the rails prevents friction. This not only increases the efficiency of the trains, but also prevents the wear and tear that makes conventional rail systems expensive to maintain. Individual Maglev train cars are also less expensive to build than conventional train cars.
Two different methods for levitating Maglev trains exist. The first, using conventional electromagnets, actually pulls guides attached to the train up toward the bottom of the track, so they are kept close but not in contact. This method requires great precision because of the small spacing required.
The other method uses superconductors on the train itself. A property of superconductors is that they can exclude magnetic fields from other magnets, which forces the two magnetic objects to maintain a space between them. Electromagnets in the track provide this magnetic field. This does not require as much precision, but the superconductors must be kept incredibly cold, which is a technical challenge.