  Considering the density wave of scalar and pseudoscalar condensates, we study
the response of quark matter to a weak external magnetic field. In an external
magnetic field, the energy spectrum of the lowest Landau level becomes
asymmetric about zero, which is closely related to chiral anomaly, and gives
rise to the spontaneous magnetization. This mechanism may be one of candidates
for the origin of the strong magnetic field in pulsars and/or magnetars.
