For a uniformly magnetized sphere, the surface magnetic field strength depends on the magnetic moment per unit volume (average magnetization) and is independent of the sphere's radius, because the magnetic moment scales with volume (proportional to R^3) while the surface dipole field formula's radius-dependence (1/R^3) exactly cancels this volume scaling when evaluated at the sphere's own surface.
The surface dipole field of a uniformly magnetized sphere is B is proportional to M/R^3, where the total magnetic moment M is proportional to (average...
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