High field magnets are superconducting alloys that must be kept under liquid helium to remain below their critical temperature. If their temperature rises above

High field magnets are superconducting alloys that must be kept under liquid helium to remain below their critical temperature. If their temperature rises above the critical temperature, they become Ohmic resistors and can melt -- or at least boil off all their cryogenic helium and nitrogen rapidly enough to be dangerous (so called quenching). Low field magnets are usually just solenoid coils. There are a number of low-field magnetic resonance devices, including benchtop relaxometers, which use either permanent magnets or electromagnets. This one just uses an electromagnet, I believe, and it looks like it's in a Helmholtz configuration. This is a smaller version of a design used primarily in veterinary contexts, e.g. so you can walk an upright horse into it. (Edit: Someone below says it's permanent magnets here. Can probably look up their patent or FDA application to be sure.)