Magnetic and structural phase transitions by annealing in tetragonal and cubic Mn3Ga thin films

Abstract

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 D0(22) tetragonal ferrimagnetic phase Mn3Ga, and the other is the disordered-L1(2) 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 degrees C) and Ar pressures (10(-3), 10(-1), and 10(3) Torr). We find that the most effective annealing temperature is 400 degrees C and their properties are the most changed by the Ar pressure. The D0(22) tetragonal ferrimagnetic phase Mn3Ga is transformed to L1(0) cubic ferromagnetic phase MnGa due to the Mn diffusion, whereas the disordered-L1(2) cubic antiferromagnetic phase Mn3Ga is converted to the ordered-L1(2) 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. (C) 2021 Elsevier B.V. All rights reserved.