Composition tuning of Mg/Ir ratio and crystallization of a spinel-related structure in Mg-Ir-O films by pulsed-laser deposition

•Control of composition in films is a crucial issue in pulsed-laser deposition.•Mg/Ir ratio in Mg-Ir-O films was regulated in 0.2 ≤ Mg/Ir ≤ 2.•Mg/Ir ratio in films increased with increasing temperature and fluence, decreasing O2 pressure.•A new Mg-Ir-O phase was crystalized in Mg-rich films.•The discovered phase was characterized as disordered inverse spinel Mg2IrO4.