We report an efficient technique for the bulk manufacture of magnetic Janus particles.  Unlike earlier methods of modifying one side of particles adsorbed on a surface, we make use of phase separation to produce a large amount of Janus particles in a single step.  These particles are spheroidal, with sizes controllable from several hundred nanometers to several microns.  The ratio between the magnetic/nonmagnetic parts is adjustable.  Few types of magnetic Janus particles have been manufactured so far, however, and their assembly has not been studied much.Our group has studied previously the dielectrophoretic assembly of metallo-dielectric Janus particles, and has discovered convenient ways to control the movement of individual particles and their assembly into 1D and 2D structures by the magnitude and frequency of the AC electric field.    We will present here the assembly of magnetic Janus colloids under the combined (and sometimes competing) dielectrophoretic and magnetophoretic forces.  While the dielectrophoretic interactions involve the electrostatic charges on the particle surfaces and the polarizability of the ionic atmosphere around them, the force exerted by the magnetic field can be independent of the dispersion medium and a conveniently modulated in a direction independent of the applied electric field.   These novel particles could serve as a tool for studying new physical phenomena and large-scale assembly, and also have numerous potential applications, among which are bifunctional drug delivery agents and novel flexible displays.