Abstract: A valve for regulating the flow of materials which are made up substantially of magnetic particles. The valve includes an outer housing and a core assembly secured within the housing to define an annular flow passage therebetween. The core assembly supports an improved magnet/coil assembly. The magnet/coil assembly includes a permanent magnet positioned between a pair of pole pieces and has an electromagnetic coil surrounding the permanent magnet. When energized, the coil establishes a counteracting magnetic field to cancel the magnetic field of the permanent magnet, which allows an open flow condition in the valve. An annular cavity is defined between the permanent magnet and the coil, which provides for a flux leakage path for the permanent magnet. During an open condition, the flux from the permanent magnet is shunted across the cavity to reduce the flux to be counteracted by the coil's magnetic field and therefore reduce the power consumed by the valve.