Spectroscopic detection of hopping induced mixed valence for Ti and Sc in $GdSc1−xTixO3$ for $x$ greater than the percolation threshold of $∼0.16$

Only two of the first row transition metals have elemental oxides that are either ferromagnetic or ferrimagnetic; these are $CrO2$ and $Fe3O4$⁠. The electron spin alignment enabling ferromagnetism and/or ferrimagnetism in these oxides is associated with a double exchange mechanism that requires mixed valence and metallic conductivity. This article describes a novel way to realize these two necessary, but insufficient conditions for double exchange magnetism. These are mixed valence and a hopping conductivity that can force intraplane electron spin alignment in a complex oxide host perovskite, $A(B,C)O3$⁠, where $A$ is an ordinary metal or $d0$ lanthanide, $B$ is a $d0$ transition metal, and $C$ is a $dn$ transition metal with $n≥1$ as, for example, in $GdS1−xTixO3$⁠. This article combines x-ray absorption spectroscopy, multiplet theory, charge transfer multiplet theory, and degeneracy removal by Jahn–Teller effect mechanisms to demonstrate mixed valence for both Sc and Ti above a percolation limit, $x>0.16$⁠, in which hopping transport gives rise to a metal to insulator transition. In this alloy, ferromagnetism/ferrimagnetism is not observed due to alternating spin alignment in sequenced $(Sc,Ti)O2$ planes.