  The detection of defect-induced magnetic order in single low-dimensional
oxide structures is in general difficult because of the relatively small yield
of magnetically ordered regions. In this work we have studied the effect of an
external magnetic field on the transient photocurrent measured after light
irradiation on different ZnO samples at room temperature. We found that a
magnetic field produces a change in the relaxation rate of the transient
photocurrent only in magnetically ordered ZnO samples. This rate can decrease
or increase with field depending whether the magnetic order region is in the
bulk or only at the surface of the ZnO sample. The phenomenon reported here is
of importance for the development of magneto-optical low-dimensional oxides
devices and provide a new guideline for the detection of magnetic order in
low-dimensional magnetic semiconductors.
