how can weaken or block the magnetic force

Weaken the magnetic can beat, broiled way, its main purpose is to allow the magnet magnetic field lines reach the chaos weaken the role of magnetism, if you have a better, you can!
But the barrier, a little difficult,  Grate Magnet because magnetic field lines can penetrate glass, paper, books, it can be metal, but I think there are three metal absorption magnetic field lines, that is, iron-cobalt-nickel, you can place a board in their midst (iron-cobalt-nickel), it is a barrier effect!
Can be a very strong magnetic rare earth permanent magnet, for ordinary Magnets "magnetizing", that suck the drum separator common magnet; wire trap can also be used in an ordinary magnet, the coil with a large current discharge method, magnetization of the magnet (typically a few hundred volts with a large capacitor is charged after the coil discharge). To the attention of the magnetization direction of the current magnetic field generated by the coil of the magnet with the same.