Soft X-ray absorption Spectroscopic Investigation on Electronic Evolutions in SrFe$_{1-x}$Mo$_x$O$_{3\pm\delta}$ (0 $\le x \le$ 1)

A double perovskite Sr$_2$FeMoO$_6$, which an alternative mixture of SrFeO$_3$ and SrMoO$_3$, is a half-metallic ferrimagnet with a high critical temperature $T_C$ $\sim$ 400K, although a certain amount of anti-site disorder diminishes the half-metallicity in a real system. SrFeO$_3$ and SrMoO$_3$, which have the ionic states of Fe$^{4+}$ and Mo$^{4+} $, are known to be an antiferromagnetic insulator and a non- magnetic metal, respectively. However, as they forms the double perovskite, the ionic states primarily form Fe$^{3+}$ (3$d^5_ {\uparrow}$) and Mo$^{5+}$ (4$d^1_{\downarrow}$) , and then the Fe 3$d$-Mo4$d$ hybridization makes a down spin band at the Fermi level. Hence the real ground state becomes a state with Fe$^{2+} $-Fe$^{3+}$ and Mo$^{5+}$-Mo$^{6+}$ mixed valences. It means that the valences of Fe and Mo can vary by two, i.e. from Fe$^ {4+}$ to Fe$^{2+}$ and from Mo$^{4+}$ to Mo$^{6+}$ in SrFe$_{1-x} $Mo$_x$O$_{3\pm\delta}$ (0$\le x \le$1), respectively. Here we presents the structural, electrical, and magnetic phase diagram and electronic evolutions in SrFe$_{1-x}$Mo$_x$O$_{3\pm\delta}$ (0$\le x \le$1).