  Mn-doped \b{eta}-Ga2O3 (GMO) films with room-temperature ferromagnetism
(RTFM) are synthesized by polymer-assisted deposition and the effects of
annealing atmosphere (air or pure O2 gas) on their structures and physical
properties are investigated. The characterizations show that the concentrations
of vacancy defects and Mn dopants in various valence states and lattice
constants of the samples are all modulated by the annealing atmosphere.
Notably, the samples annealed in air (GMO-air) exhibit a saturation
magnetization as strong as 170% times that of the samples annealed in pure O2
gas (GMO-O2), which can be quantitatively explained by oxygen vacancy (VO)
controlled ferromagnetism due to bound magnetic polarons established between
delocalized hydrogenic electrons of VOs and local magnetic moments of Mn2+,
Mn3+, and Mn4+ ions in the samples. Our results provide insights into
mechanism-based tuning of RTFM in Ga2O3 and may be useful for design,
fabrication, and application of related spintronic materials.
