Permanent magnet assemblies include a central cylindrical magnet having a bore. The cylindrical magnet is magnetized along a selected radial direction and is enclosed within a ferromagnetic shim. A uniform magnetic field, field gradient, or other field distribution can be produced in the bore based on the bore cross-sectional shape.
ACKNOWLEDGMENT OF GOVERNMENT SUPPORT
 This invention was made with government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The government has certain rights in the invention.