The effect of intrinsic magnetic properties on permanent magnet repulsion

Magnetic repulsion is currently under active consideration as a means for providing quiet, frictionless suspension for future tracked ground transportation vehicles and for providing high-reliability, long-lived, friction-free bearings for unique new devices and components. Analytical and experimental results indicate that the superior intrinsic magnetic properties of certain members of a new class of permanent magnet materials, the rare-earth-cobalts (including PrCo 5 and SmCo 5 ), have intrinsic magnetic properties that make them outstanding candidates for such applications. Experimental results verify analytical predictions that repulsive force characteristics of permanent magnet pairs are critically dependent on intrinsic magnetic properties. The repulsive force is shown to be proportional to the product of the magnetizations MM' of the opposing magnets, which, in turn, depend on the magnetization versus demagnetizing field ( M versus H ) characteristics of the magnets. It is predicted that magnets will produce repulsive force in total demagnetizing fields less than their intrinsic coercive force |H T |< M H c ; i.e., their intrinsic coercive force can be considered the limiting field value for repulsion operation. Permanent magnet materials suitable for repulsion applications include the barium ferrites and platinum cobalt as well as the rare-earth-cobalts. The intrinsic characteristics of the Alnicos make them unsuitable for repulsion applications. Experiments show that PrCo 5 magnets having twice the residual magnetization M r of oriented barium ferrite magnets of similar size and shape produce four times the repulsive force. PrCo 5 magnets with maximum theoretical magnetization would provide about eleven times the repulsive force of similar barium ferrite magnets.