Microstructures and Magnetic Properties of Rapidly Solidified MnAl Alloys Modified with Indium

A ternary Mn–Al–In alloy with the nominal composition MnAlIn were prepared by rapid solidification followed by heat treatment. Doping in MnAl alloys can improve the stability of the τ-phase when the annealing temperature is lower than 600 °C. The decomposition of τ-phase started after annealing at 500 °C for 30 min and almost completed after annealing at 650 °C for 30 min. It was found that most of the In-rich phases in as-spun alloys are generally distributed on the grain boundary of magnetic τ-MnAl. After annealing, the small ball-shaped β-phase particles were precipitated on the surface of τ-MnAl grains. The average particle size of β-phase increased sharply from about 73 nm to about 830 nm with the increasing annealing time from 10 to 30 min at 550 °C. The optimal magnetic properties of M = 105.7 emu/g and H = 1.094 kOe were obtained in the ribbons after annealing at 550 °C for 10 min. The highest value of the H was 4.261 kOe achieved in the MnAlIn ribbons after annealing at 650 °C for 30 min. However, the high coercivity was obtained at an expense of low saturation magnetization.