"The idea of magnetic trapping is that in a magnetic field, an atom with a magnetic moment will have quantum states whose magnetic or Zeeman energy increases with increasing field and states whose energy decreases, depending on the orientation of the moment compared to the field. The increasing-energy states, or low-field-seekers, can be trapped in a magnetic field configuration having a point where the magnitude of the field is a relative minimum. [No dc field can have a relative maximum in free space (Wing, 1984), so high-field-seekers cannot be trapped.] The requirement for stable trapping, besides the kinetic energy of the atom being low enough, is that the magnetic moment move adiabatically in the field. That is, the orientation of the magnetic moment with respect to the field should not change."
January 1, 1970
https://en.wikiquote.org/wiki/William_Daniel_Phillips