  We employ a recently developed three-dimensional semiclassical model to
identify nondipole effects in triple ionization of Ne driven by infrared laser
pulses at intensities where electron-electron correlation prevails. This model
fully accounts for the Coulomb interaction of each electron with the core and
avoids artificial autoionization by employing effective Coulomb potentials to
describe the interaction between bound electrons (ECBB). Using the ECBB model,
we identify a prominent signature of nondipole effects. Namely, the component
along the direction of light propagation of the average sum of the final
electron momenta is large and positive. That is, we identify a positive
momentum offset, absent in the dipole approximation. We find that this positive
momentum offset stems mostly from the momentum change due to the magnetic
field. To further understand this momentum change, we also develop a simple
model for the motion of an electron inside an electromagnetic field. This
simple model accounts for the effect of the Coulomb forces only as a sharp
change in the momentum of the electron during recollision. We show that the
momentum change due to the magnetic field is related with the sharp change in
momentum during recollision for the recolliding electron as well as with the
time of recollision for both the recolliding and bound electrons. Hence, we
demonstrate that the final electron momentum offset probes the strength of a
recollision and hence the degree of correlation in multielectron ionization.
