  Lattice simulations for (2+1)-flavor QCD with external magnetic field
demonstrated that the quark mass is one of the important parameters responsible
for the (inverse) magnetic catalysis. We discuss the dependences of chiral
condensates and susceptibilities, the Polyakov loop on the magnetic field and
quark mass in three degenerate flavor QCD. The lattice simulations are
performed using standard staggered fermions and the plaquette action with
spatial sizes Ns = 16 and 24 and a fixed temporal size Nt = 4. The value of the
quark masses are chosen such that the system undergoes a first order chiral
phase transition and crossover with zero magnetic field. We find that in light
mass regime, the quark chiral condensate undergoes magnetic catalysis in the
whole temperature region and the phase transition tend to become stronger as
the magnetic field increases. In crossover regime, deconfinement transition
temperature is shifted by the magnetic field when quark mass ma is less than
0.4. The lattice cutoff effects are also discussed.
