The oxygen dependence of the magnetic structure for Sr3Fe2O7-δ

We have measured the magnetization of single crystalline Sr3Fe2O6.5 with a lot of oxygen deficiencies. It was observed that the spin direction is parallel to the c-axis below T-N. Moreover, we carried out neutron powder diffraction experiments with a Sr3Fe2O6.21 powder sample.. The magnetic structure with a lot of oxygen deficiencies (delta > 0.5) has a typical Ising antiferromagnet system with the magnetic unit cell root2a x root2a x c. On the other hand, it was found that the magnetic structure Of Sr3Fe2O6.94 with a few oxygen deficiencies is larger than that of 2a x 2a x 4c. The magnetic structure of Sr3Fe2O6.94 is obviously different from that of Sr3Fe2O7-delta (8 > 0.5). Such a difference in the magnetic structures is associated with a drastic change of the exchange interactions between Fe-spins due to the introduction of oxygen.