An increased thermodynamic stability of the ferromagnetic τ-phase in Ga-doped Mn-Al alloys allows to investigate the influence of mechanical stress on structural state and the key magnetic properties of the material. This work focuses on the determination of the structural state and magnetic properties, as well as their correlation, of Mn55Al36Ga9 powder during milling. Herein, an ingot with the nominal composition of Mn55Al36Ga9 was fabricated via induction melting. It was then homogenized, quenched and annealed in order to obtain a high concentration of the τ-phase, and was subsequently grinded in a low-energy mode using a planetary ball mill for 1, 3 and 6hours. The chosen milling regime, without an addition of surfactants, resulted in a formation of anisotropic flake-like particles, which primarily consisted of τ-phase. An absence of considerable changes in τ-phase content during the ball-milling shows its’ stability to degradation via the process. However, annealing of the milled Mn55Al36Ga9 powder at 700 °C for 20minutes led to an intensive decomposition of the τ-phase with formation of β-Mn. The coercive force (Hc) reaches 217kA/m after 6hours of grinding, while maximum magnetization Imax value reaches 356kA/m after 20min of annealing following 6hours of milling. This is due to a decrease in the antiferromagnetic exchange interaction between Mn atoms. Structural studies of the milled and annealed powders were provided by scanning and transmission electron microscopy, atomic-force microscopy and X-Ray diffraction analysis.
Read full abstract7-days of FREE Audio papers, translation & more with Prime
7-days of FREE Prime access