![]() A doubling of the Hc without sacrificing Br can possibly improve the (BH) max from the current best of 10.5 MGOe (83.5 kJ/m 3) to ∼ 21 MGOe (167.1 kJ/m 3) ( Zhou et al., 2014, 2017). This deficiency is attributed to a non-optimal microstructure that renders magnetization reversal by lower energy pathways. Moreover, due to current strategic materials supply issues, this family of magnets has received renewed attention.Īlthough the shape anisotropy of the FeCo parallelepipeds acts as a basis of coercivity, a recent analysis indicates that the achieved coercivity is not taking full advantage of the available magnetocrystalline anisotropy ( Zhou et al., 2014). The textured Alnico magnets are referred by their grade as Alnico 5–7, Alnico 8, and Alnico 9, and their magnetic parameters are listed in Table 2. Commercial Alnico alloys have maximum energy products in the range of 5–10 MGOe (39.8–79.6 kJ/m 3). The process resulted in the formation of aligned elongated FeCo precipitates with 〈001〉 texture ( Luborsky et al., 1957). An anisotropic microstructure containing elongated FeCo is attained by the application of magnetic field during the annealing process. The early Alnico magnets contained randomly oriented FeCo parallelepipeds and thus exhibited low coercivity ( Zhou et al., 2014, 2017). In addition, the high-temperature annealing process forms elongated parallelepipeds of FeCo that possess considerably shape anisotropy and hence robust coercivity. However, the decomposition rate is adequately high at elevated temperature, and these two phases develop by a gradual fluctuation in composition rather than by more typical nucleation and growth processes. The weak K 1 is not sufficient to induce a reasonable coercivity. As a result, the magnetocrystalline anisotropy ( K 1) is one order of magnitude lower than that of the uniaxial Nd-Fe-B compound. The M S and T C mainly derive from the FeCo constituent, which is present in the cubic phase with three equivalent easy axes. The magnetic strength of the Alnico alloys originates by virtue of a phase separation in the cast alloy into ferromagnetic FeCo-rich and weakly magnetic NiAl-rich phases precipitated from the high-temperature homogeneous composition. The Alnico magnets are one of the first so-called “nanocomposites” magnets, having a microstructures consisting of submicron-size ferromagnetic particles dispersed in a weakly magnetic matrix ( Lewis and Jiménez-Villacorta, 2013).
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