Structural and Magnetic Properties of Mnal Prepared by Cryo-Milling

Abstract

The structure and magnetic properties of cryo-milled MnAl samples were studied by X-ray and neutron diffraction, scanning electron microscope, and magnetic measurements. A quantitative model was introduced to explain the relationship between magnetization and the magnetic structure. It was found that the decrease of the magnetization with increasing milling time is mainly due to the migration of Mn atoms to the 1d site and the decrease of Mn atomic magnetic moment. The τ-phase MnAl, with a high coercivity of up to 4.9 kOe, can be obtained by cryo-milling for 100 minutes. The increase of coercivity in the cryo-milling process is mainly related to the grain size refinement and the induced stress effects. With the increase of cryo-milling time, the grain size D reduced continuously from 145 nm to 36 nm when the sample was milled for 120 minutes. Moreover, the stress gradually accumulated and reached a maximum of 2.24% when the sample was milled for 80 minutes, then decreased. Compared to the ball milling method, cryo-milling shows an advantage in faster grain refinements and suppression of powder agglomeration with improved coercivity.

Keywords: MnAl, Magnetic properties, crystal and magnetic structure, cryo-milling, neutron powder diffraction