Dependence of the permanent magnet properties of Mn55Al45on particle size

The magnetic properties of the alloy Mn55Al45in its metastable ferromagnetic state have been investigated as a function of particle size in the range 1000μm down to about 20μm. It has been shown that the coercivity rises very rapidly as the particle size decreases but the remanence was shown to increase slowly and then to decrease rapidly due to the disorder resulting from the plastic deformation during grinding. The maximum intrinsic coercivity of 5 KOe was obtained for 63-75 μm particles while the maximum remanence of 60 e.m.u/g was obtained for 125-150 μm particles. The best potential permanent magnet properties were obtained for 125-150 μm particles viz,(BH_{\max} = 2.2MGOe,B_{r} = 4.2KG, andBHc= 2 kOe.