Antiferromagnetic Order in Epitaxial FeSe Films on SrTiO3

Single monolayer FeSe film grown on a Nb-doped SrTiO3(001) substrate shows the highest superconducting transition temperature (T-C similar to 100 K) among the iron-based superconductors ( iron pnictides), while the TC value of bulk FeSe is only similar to 8 K. Although bulk FeSe does not show antiferromagnetic order, calculations suggest that the parent FeSe/SrTiO3 films are antiferromagnetic. Experimentally, because of a lack of a direct probe, the magnetic state of FeSe/SrTiO3 films remains mysterious. Here, we report direct evidence of antiferromagnetic order in the parent FeSe/SrTiO3 films by the magnetic exchange bias effect measurements. The magnetic blocking temperature is similar to 140 K for a single monolayer film. The antiferromagnetic order disappears after electron doping.