Universal robustness of bound magnetic polaron scaling and enhancement of ferromagnetism in amorphous gallium oxide via aliovalent Sn doping over oxygen vacancies.

The bound magnetic polaron (BMP) model underpins room-temperature ferromagnetism in oxide diluted magnetic semiconductors, predicting a scaling law for the Curie temperature (TC) as TC ∝ (xδ)0.5. However, this paradigm relies exclusively on oxygen vacancies (VO), whose heavy and localized electrons intrinsically limit magnetic coupling strength. A critical question remains: does this scaling law hold when the donor electron's microscopic nature is fundamentally altered? Here, our work addresses this by introducing substitutional Sn4+ as an aliovalent donor into amorphous (Fe,Sn)-codoped Ga2O3 thin films. Sn4+ provides lighter and more spatially extended electrons with a Bohr radius ∼1.5 times larger than VO-related electrons. Remarkably, despite this qualitative shift, the Coey scaling law persists with an exponent of 0.54, validating its robustness against donor physics. Leveraging the enhanced contribution of Sn to BMP formation, which is 2.2 times that of VO, and the amorphous matrix's stabilization for the high defect density required for BMP nucleation, we achieve a record TC of ∼342 K and saturation magnetization (MS) of ∼170 emu cm-3. This work establishes aliovalent doping as a superior strategy to defect engineering, providing the first experimental proof of the BMP law's universality for designing high-performance oxide spintronics.