Oxygen vacancy-dependent microstructural, optical and magnetic properties of sol-gel Tb0.2 Er1 Y2.8 Fe5 O12 films

•The pure phase of Tb, Er doped YIG films was easily grown by a sol-gel method.•The lattice constant decreases with higher Er content.•Adding Er ions reduces the saturation magnetization and increases the coercivity.•An improvement in optical transparency with increment of Er content was observed. A garnet, composition of Tb0.2 Er1 Y1.8 Fe5 O12, based nanostructure thin films were prepared by a sol-gel method for a magneto-optical isolator. The films were deposited on a quartz substrate and crystallised at 900 °C under different annealing environments (air, oxygen and argon). Fe2+ concentration-dependent, microstructural, optical and magnetic properties were investigated systematically. This study shows that Fe2+ ions are dominant in the air-annealed film with an atomic percentage of 77.63%, which results in the expansion of the unit cell. In addition, an excess of Fe2+ ions results in much higher optical absorption, remanent magnetisation and saturation magnetisation, caused by the migration of oxygen vacancies due to the reduction of Fe3+ to Fe2+. Conversely, annealing in oxygen and argon gases suppresses the formation of oxygen vacancies, hence improves the optical and magnetic properties of the films. Low saturation magnetisation, combined with low optical absorption, is highly desirable in magneto-optical applications.