  We have explored a new mechanism for switching magnetism and
superconductivity in a magnetically frustrated iron-based superconductor using
spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single
crystal Sr$_2$VO$_3$FeAs shows that a spin-polarized tunneling current can
switch the Fe-layer magnetism into a non-trivial $C_4$ (2$\times$2) order, not
achievable by thermal excitation with unpolarized current. Our tunneling
spectroscopy study shows that the induced $C_4$ (2$\times$2) order has
characteristics of plaquette antiferromagnetic order in Fe layer and strongly
suppressed superconductivity. Also, thermal agitation beyond the bulk Fe spin
ordering temperature erases the $C_4$ state. These results suggest a new
possibility of switching local superconductivity by changing the symmetry of
magnetic order with spin-polarized and unpolarized tunneling currents in
iron-based superconductors.
