This invention relates to magnetic assemblies and, in particular, to assemblies which are useful for inducing magnetic fields within vacuum chambers. Thus a magnetic assembly, generally indicated at 10, includes the rectangular magnetically soft core 11 carrying windings 12, which together form the main planar electromagnet, generally indicated at 13, and immediately adjacent the edges of the magnet 13 are placed auxiliary coils 14. Coils 14 are each formed from windings 15 wound around oblate cores 16 and it would be noted that they project upwardly above the upper surface of the planar magnet 13. Pole pieces 17 are attached to the ends of the planar magnet 13 and these two project above the upper surface of the planar magnet 13. The assembly is completed by mounting brackets 18.