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 TN. Moreover, we carried out neutron powder diffraction experiments with a Sr3Fe2O6.21 powder sample. The magnetic structure with a lot of oxygen deficiencies (δ>0.5) has a typical Ising antiferromagnet system with the magnetic unit cell \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sqrt\Box2\Box$\end{document}a×\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sqrt\Box2\Box$\end{document}a×c.