Magnetic and structural phase transitions by annealing in tetragonal and cubic Mn3Ga thin films
Thermal Annealing is a simple and powerful tool to improve the crystallinity in general or promote the functionality for peculiar purposes, ultimately leading to metastable states with lower energy. We report the annealing effect focusing primarily on the structural and magnetic properties of two different Mn3Ga thin films. One is the D022 tetragonal ferrimagnetic phase Mn3Ga, and the other is the disordered-L12 cubic antiferromagnetic phase Mn3Ga. They were grown by RF/DC magnetron sputtering method on MgO substrate. After deposition, the thin films were annealed at various temperatures (200, 300, 400, 500, and 600 °C) and Ar pressures (10？3, 10？1, and 103 Torr). We find that the most effective annealing temperature is 400 °C and their properties are the most changed by the Ar pressure. The D022 tetragonal ferrimagnetic phase Mn3Ga is transformed to L10 cubic ferromagnetic phase MnGa due to the Mn diffusion, whereas the disordered-L12 cubic antiferromagnetic phase Mn3Ga is converted to the ordered-L12 cubic ferrimagnetic phase within the Mn3Ga phase. We discuss the structural and magnetic properties of each phase to unveil the mechanism of both phase transitions. These results will provide a better understanding of the magnetic phase transition with the structural phase transition in the composition-sensitive Heusler thin films.