Tailoring the magnetic properties of Ce-Fe-B alloys by controlling the CeFe2 paramagnetic phase

Abstract

The CeFe₂ paramagnetic phase consumes a large amount of Ce in the Ce-Fe-B, deteriorating the magnetic properties of the alloys. Due to the significant consumption of Ce element in the CeFe₂ phase, the content of Ce is maintained at a high level, i.e., up to 35–37 wt% in the Ce-Fe-B alloys. In this paper, we report the magnetic properties of Ce-Fe-B alloys by adding Ge, which suppresses the formation of the CeFe₂ phase. The content of Ce is reduced from 35 to 28.5 wt%, resulting in a significant reduction in the volume fraction of the CeFe₂ from 10.3 wt% in the Ce₃₅Fe_63.5Ge_0.5B alloy to 1.6 wt% in the Ce_31.1Fe_67.4Ge_0.5B alloy. The soft magnetic α-Fe phase is formed when the content of Ce is reduced to 29.8 and 28.5 wt%. The intrinsic coercivity of the alloys decreased from 490 kA/m in the pristine alloy to 410 kA/m in the Ce_29.8Fe_68.7Ge_0.5B alloy. The remanence of the alloys increased from 0.46 T in the pristine alloy to 0.59 T in the Ce_29.8Fe_68.7Ge_0.5B alloy. More strikingly, the maximum energy density, which is the figure of merit for permanent magnets, increased from 33.8 kJ/m³ to 52.3 kJ/m³, showing an increment of ∼55 %. The phase constituents, microstructure, phase transition temperatures, magnetic interactions, and applicability of the alloys have been investigated in detail using XRD Rietveld refinement, transmission electron microscopy and various magnetic property measurements.