We give a theoretical treatment of magnetic dipole absorption of
electromagnetic radiation in small conducting particles, at photon energies
which are large compared to the single particle level spacing, and small
compared to the plasma frequency. We discuss both diffusive and ballistic
electron dynamics for particles of arbitrary shape.
The conductivity becomes non-local when the frequency is smaller than the
frequency \omega_c characterising the transit of electrons from one side of the
particle to the other, but in the diffusive case \omega_c plays no role in
determining the absorption coefficient. In the ballistic case, the absorption
coefficient is proportional to \omega^2 for \omega << \omega_c, but is a
decreasing function of \omega for \omega >> \omega_c.Comment: 25 pages of plain TeX, 2 postscipt figure