Cation-placement control in double-perovskite GdBaCo2O6 and its impact on magnetism via spin-state modification

Double-perovskite GdBaCo2Ox exhibits remarkable magnetic properties, including half-metallicity, high magnetic anisotropy, and photoinduced magnetic phase transition. While manipulating these properties through cation arrangement is attractive, addressing the thermodynamic stability of the Gd/Ba order necessitates an unconventional synthesis approach. Herein, we report the synthesis of both A-site-ordered and -disordered GdBaCo2O6 films employing a combination of substrate-induced strain and low-temperature topochemical oxidation reactions. Both types of films displayed metallic and ferromagnetic behaviors. Interestingly, the A-site-disordered film exhibited superior magnetization (11.5 mu(B) f.u.(-1) at 40 kOe), a higher Curie temperature (T-C = 165 K), and lower resistivity compared to the A-site-ordered film (9.5 mu(B) f.u.(-1) at 40 kOe; T-C = 115 K). Theoretical calculations predicted that the alterations in the magnetic and conductive properties of the A-site-disordered film stem from a change in its Co spin states associated with a change in ion arrangement. This mechanism diverges from conventional double perovskites, where magnetic properties primarily stem from alterations in the combination of nearest-neighbor magnetic elements or lattice parameters without affecting the spin state. Our results highlight the potential of unconventional synthesis strategies in broadening the tunability of functionalities in double-perovskite materials and manipulating spin states through cation-placement control.