Out-of-roundness and thermal energy effects on 'ideally soft ferromagnets'

Infinite initial susceptibility is predicted in certain micro-magnetic comp utations of sufficiently small spheres and circular discs made of isotropic magnetic material. In this letter, it is argued that this result pertains only to perfectly round samples in the absence of thermal energy. It is exp ected, therefore, that much lower values of the initial susceptibility will be found on experimentally realizable samples at room temperature. (C) 200 1 Elsevier Science B.V. All rights reserved.