  The iron calorimeter (ICAL) detector at the India-based Neutrino Observatory
(INO) will be used to measure neutrino mass hierarchy. The magnet in the ICAL
detector will be used to distinguish the {\mu^-} and {\mu^+} events induced by
{\nu_{\mu}} and {\bar{\nu_{\mu}}}, respectively. Due to the importance of the
magnet in ICAL, an electromagnetic simulation has been carried out to study the
B-field distribution in iron using various designs. The simulation shows better
uniformity in the portion of the iron layer between the coils, which is bounded
by regions which have lesser field strength as we move to the periphery of the
iron layer. The ICAL magnet was configured to have a tiling structure that gave
the minimum reluctance path while keeping a reasonably uniform field
pattern.This translates into less Ampere-turns needed for generation of the
required magnetic field. At low Ampere-turns, a larger fractional area with
\vert B \vert \ge 1 Tesla (T) can be obtained by using a soft magnetic
material. A study of the effect of the magnetic field on muon trajectories has
been carried out using GEANT4. For muons up to 20 GeV, the energy resolution
improves as the magnetic field increases from 1.1T to 1.8T. The charge
identification efficiency for muons was found to be more than 90\% except for
large zenith angles.
