A magnet, such as an open magnetic-resonance-imaging (MRI) magnet) has a first assembly including a superconductive main coil and a magnetizable pole piece which, during magnet operation, has a temperature equal to generally the temperature of the main coil. In one example, a cryogenic-fluid (e.g., liquid helium) dewar encloses the main coil, and the dewar has an interior surface defined in part by a surface portion of the pole piece. A method for providing a homogeneous imaging volume for a magnet includes steps to construct the above-described magnet.