  The extrapolation of nucleon magnetic form factors calculated within lattice
QCD is investigated within a framework based upon heavy baryon chiral
effective-field theory. All one-loop graphs are considered at arbitrary
momentum transfer and all octet and decuplet baryons are included in the
intermediate states. Finite range regularisation is applied to improve the
convergence in the quark-mass expansion. At each value of the momentum transfer
($Q^2$), a separate extrapolation to the physical pion mass is carried out as a
function of $m_\pi$ alone. Because of the large values of $Q^2$ involved, the
role of the pion form factor in the standard pion-loop integrals is also
investigated. The resulting values of the form factors at the physical pion
mass are compared with experimental data as a function of $Q^2$ and demonstrate
the utility and accuracy of the chiral extrapolation methods presented herein.
