Origin of coercivity in an anisotropic Sm(Fe, Ti, V)12-based sintered magnet. (15th September 2021)

• Record Type: Journal Article
• Authors: Zhang, J. S.; Tang, Xin; Sepehri-Amin, H.; Srinithi, A. K.; Ohkubo, T.; Hono, K.
• Is Part Of: Acta materialia. Volume 217(2021)
• Publication Date: 2021-09-15
• Subjects: SmFe12-based sintered magnet -- Coercivity -- Microstructure -- Intergranular phase; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2021.117161
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: We have demonstrated an anisotropic bulk SmFe12 -based sintered magnet with sufficiently large coercivity of μ 0 H c =1.0 T and a remanence ratio ( M r / M s ) of 0.84 using conventional liquid sintering process of nitrogen jet-milled powders with the nominal composition of Sm8 Fe73.5 Ti8 V8 Ga0.5 Al2 (at.%). The moderate saturation magnetization of μ 0 M s =0.74 T is due to the dissolution of a large amount of stabilizing elements, Ti, V, and Al, in the 1:12 phase. The anisotropy field of the main 1:12 phase was determined to be µ0 H A =10.2 T. Detailed multi-scale microstructure characterizations by scanning electron microscope (SEM) and scanning transmission electron microscope (STEM) showed the magnet consists of Sm(Fe, Ti, V, Al)12 grains with the ThMn12 -type crystal structure with a size distribution of ~3 − 15 µm that are enveloped by ~3 nm thick Sm-rich amorphous intergranular phase. Secondary phases including metallic (Sm, Ga)-rich, SmOx, and Fe2 (Ti, V) phases coexist with the 1:12 phase. Measured angular dependence of coercivity follows Kondorsky type magnetization reversal, suggesting the coercivity arises due to the pining of magnetic domain walls. Magneto-optical Kerr effect (MOKE) microscopy revealed magnetization reversal starts at the grain boundaries and interphase interfaces and thin amorphous intergranular phases act as the pinning sites against magnetic domain wall propagation. Small micromagnetic parameter α ~0.164 estimated by fitting to the Kronmüllar equation suggest that the reduction of the grain size and engineering of the intergranular phase to an Fe-lean composition are necessary to improve the coercivity toward µ0 H A /3 = 3.4 T. This work provides guidelines on an optimum microstructure to develop an anisotropic bulk SmFe12 -based sintered magnet with a sufficiently large coercivity. Graphical abstract: Image, graphical abstract