  We demonstrate an efficient swithcable spintronic THz emission from a
Co(2nm)/Pt(2nm) bilayer split into a grating of micro- or nanostripes in
applied external magnetic field of the order of 10mT. The THz signal is
effectively emitted if the samples are magnetized perpendicular to the stripes
direction and decreases upon a 90-degree rotation of a sample. The maximal
27-fold ratio of amplitude change is achieved for the sample with a $2 \mu m$
width of stripes. For the samples with easy magnetization axis directed
perpendicular to stripes the THz signal is linearly polarized in the direction
of the stripes and abruptly switches during the sample re-magnetization
process. If the easy axis is along the stripes the THz source is almost
switched off in a zero magnetic field.
