Effect of mechanical milling and heat treatment on the structure and magnetic properties of gas atomized Mn–Al alloy powders

Ferromagnetic Mn–Al alloy powders were fabricated by mechanical milling and heat treatment with gas-atomized powders. Different processes, i.e., heat treatment before ball milling and ball milling before heat treatment, result in different microstructures and magnetic properties of the powders. It was found that Hc increased and Mr decreased with the size reduction regardless of the sequence of heat treatment and ball milling. However, tendency of the change in Hc and Mr depended on the sequence. Further annealing of the powders ball-milled after heat treatment resulted in slight decrease of Hc and large increase of Mr. The magnetic properties, Mr = 41.2 emu/g, Hc = 3.1 kOe, were obtained from the powders ball-milled for 5 h after heat treatment at 650 °C for 20 min, and subsequent annealing at 280 °C for 20 min.