Synthesis of ferromagnetic τ phase of Mn-Al films by sputtering

Abstract

Mn‐Al films have been prepared by dc magnetron sputtering and their crystallographic characteristics, magnetic properties, electrical resistivity, and internal stress have been investigated. The films deposited when substrate temperature T_s was below 100 °C and above 170 °C exhibit a high‐temperature ε phase and β‐Mn–like structure, respectively. Films of a ferromagnetic τ phase were synthesized with Mn content in the range of 58–62 at. % and T_s of about 150 °C. Existence of CuAu‐type superstructure in the τ phase was confirmed by a change of electrical resistivity ρ of deposited films. The films deposited at a T_s of about 150 °C exhibit minimum value of 180 μΩ cm. Lattice constant a and c of the tetragonal τ‐phase crystallites in the films were in the range of 3.582–3.592 Å and 3.941–3.968 Å, respectively, while those of the bulk alloy were 3.580 and 3.940 Å, respectively. The maximum value of saturation magnetization of the films was 120 emu/cc, being as small as about one fourth of that of bulk alloy. This may be caused by elongation of lattice constants and coexistence of nonmagnetic ε phase.