Effects of Sm content on the phase structure, microstructure and magnetic properties of the SmxZr0.2(Fe0·8Co0.2)11.5Ti0.5 (x=0.8–1.4) alloys

Abstract To introduce a paramagnetic intergranular phase into the ThMn12-type permanent materials, SmFe12-based alloys with the composition of SmxZr0.2(Fe0.8Co0.2)11.5Ti0.5 (x = 0.8–1.4, at.%) are designed and prepared by arc-melting and melt-spinning. Roles of extra Sm on the phase constitution and magnetic properties are systematically investigated. First of all, within the range of x = 0.8–1.2, the as-cast ingots mainly constitute of 1:12, 1:10, 1:2 and α-(Fe,Co) phase. With increasing Sm content, both 1:12 and α-(Fe,Co) phases decrease whereas 1:2 and 1:10 phases increase. Similarly, for the heat-treated ribbons with x = 0.8–1.2, α-(Fe,Co) phase also decreases with the increasing Sm content. Consequently, the Js and Jr of the alloys exhibit a decreasing trend while the Hc and (BH)max show an increasing trend. As a result, excellent magnetic properties of Jr = 1.04 T for x = 0.8 alloy, (BH)max = 61 kJ/m3 and Hc = 3.0 kOe for x = 1.2 alloys are acquired. Henkel curves of the annealed ribbons prove the existence of an exchange coupling effect in all alloys, which has contributed to the remanence enhancement. Interestingly, the observed kink in the demagnetization curve of x = 1.2 annealed alloy suggests the ineffective exchange coupling between soft and hard grains. An amorphous grain boundary phase is observed in the annealed x = 1.2 alloy while the refined 57Fe Mossbauer spectrum confirms its paramagnetic behavior. The present work may provide a dependable guideline for designing the composition and microstructure of 1:12-based permanent material.