Hexaferrite materials displaying ultra-high coercivity and sub-terahertz ferromagnetic resonance frequencies

Structural and magnetic properties of RE-Al substituted nanocrystalline hexaferrites (Sr1−xRExAl2Fe10O19)

“…Further, the magnetic parameters for the STAF and SDAF samples were similar to the highest parameters reported for other RE substituted SrAl 2 Fe 10 O 19 samples [27]. However, in a recent study [40], it was shown that the Ca-Al substitution in SrM hexaferrites was more effective, were a coercivity of 21.3 kOe, close to the higher end of the coercivity of the Sm-Co magnets, was reported for Sr 0.67 Ca 0.33 Fe 8 Al 4 O 19 compound. The Ca-Al substituted ferrites, in spite of the rather low saturation magnetization they exhibited, demonstrated potential for the production of low cost materials with very high coercivity and sub-terahertz natural ferromagnetic resonance [40].…”

Synthesis of red mud derived M-type barium hexaferrites with tuneable coercivity

“…For example, M s is reported as being only 30.2 A m 2 /kg for BaAl 2 Fe 10 O 19 [57], ~22 A m 2 / kg for BaAl 2.5 Fe 9.5 O 19 [58], 45 A m 2 /kg in BaCoTiFe 10 O 19 [59] (in which H c also decreases), and only 42 and 29 A m 2 /kg for BaAl 2.5 Fe 9.5 O 19 and BaAl 3.5 Fe 8.5 O 19 , respectively, with H c ~170 kA/m for both [60]. In a study of Al substituted SrM, it was found that [55] and a massive maximum of ~2870 kA/m for Sr 0.54 Ca 0.46 Fe 6.5 Al 5.5 O 19 [63]. Therefore, although we cannot definitely say what the composition is of this BaM ferrite, we can estimate that it has a considerable content of nonmagnetic 3 + and 4 + ions, and this would consequently greatly reduce its magnetisation.…”

Glass-Ceramic Synthesis of Cr-Substituted Strontium Hexaferrite Nanoparticles with Enhanced Coercivity

“…Typical reported colloidal hexaferrite nanoparticles with diameters of 10-100 nm display coercivity values between zero and 360 kA m −1 (4500 Oe) for the largest particles [7,15,[22][23][24]. A common way to increase the coercivity of the hexaferrites is the partial substitution of iron ions with aluminum [1,3,21,[25][26][27], e.g., this can result in a coercivity of submicron single-domain particles of up to 3180 kA m −1 (40 kOe) [25]. However, the aluminum substitution requires high annealing temperatures above 1000 • C, which makes the preparation of nanoparticles quite challenging.…”