  We study the effect of magnetic field on heavy quark-antiquark pair in both
Einstein-Maxwell(EM) and Einstein-Maxwell-Dilaton(EMD) model. The interquark
distance, free energy, entropy, binding energy and internal energy of the heavy
quarkonium are calculated. It is found that the free energy suppresses and the
entropy increases quickly with the increase of the magnetic field $B$. The
binding energy vanishes at smaller distance when increasing the magnetic field,
which indicates the quark-antiquark pair dissociates at smaller distance. The
internal energy which consists of free energy and entropy will increase at
large separating distance for non-vanishing magnetic field. These conclusions
are consistent both in the EM and EMD model. Moreover, we also find that the
quarkonium will dissociate easier in the parallel direction than that in the
transverse direction for EMD model, but the conclusion is opposite in EM model.
Lattice results are in favor of EMD model. Besides, a Coulomb-plus-linear
potential(Cornell potential) can be realized only in EMD model. Thus, a dilaton
field is proved to be important in holographic model. Finally, we also show
that the free energy, entropy and internal energy of a single quark in EMD
model with the presence of magnetic field.
