An integral motor pump (IMP) or turbine (IMT) applicable to a low temperature process liquid, such as liquid hydrogen, includes an impeller having an annular ring of permanent magnets attached thereto passing in axial proximity to a plurality of stator coils. The magnet ring is radially bounded by inner and outer compression sleeves having coefficients of expansion (CTEs) respectively less than and greater than the CTE of the magnets. Unequal thermal contraction of the compression sleeves, when cooled by the process liquid, applies radial compression to the magnet ring, overcoming centrifugal forces and maintains the magnets in radial compression, thereby preventing fracturing or pulverizing of the magnets. The magnet ring can be a monolithic ring with alternating magnetic regions, a ring of closely abutting magnets, or a ring of discrete magnets surrounded by a barrier material having a CTE equal to the magnet CTE.