Preparation and Magnetic Properties of SrFe₁₂O₁₉Ferrites Suitable for Use in Self-Biased LTCC Circulators

Abstract

Strontium ferrites with different Bi2O3 content are prepared by the solid phase method, and their magnetic properties are investigated primarily. The Bi2O3 additive and sintering temperature separately exhibit a strong effect on the sintering density, crystal structure, and magnetic properties of the ferrites. As to the ferrites with 3 wt% Bi2O3, the relatively high sintering density 𝜌s, saturation magnetization 𝑀s, and intrinsic coercivity 𝐻ci can be obtained at a low sintering temperature of 900 ∘ C even much lower. Furthermore, the effective magnetic anisotropy constant 𝐾 eff and magnetic anisotropy field 𝐻a of the ferrites are calculated from the magnetization curve by the law of approach to saturation. It is suggested that the low-temperature sintered SrFe12O19 ferrites with 𝑀s of 285.6 kA/m and 𝐻a of 1564.6 kA/m possess a significant potentiality for applying in the self-biased low-temperature co-fired ceramics circulators from 34 to 40 GHz.

Effect of La–CO substitution on the crystal structure and magnetic properties of low temperature sintered Sr1−La Fe12−Co O19 (x=0–0.5) ferrites

“…It is well known that the sintering temperature of M-type hexaferrites usually reaches above 1200°C, and Fe 2 O 3 cannot fully participate in the reaction to produce M-type phase at low sintering temperatures. But the appropriate addition of Bi 2 O 3 promotes the formation of M-type phase at low sintering temperatures, which is strongly correlated with the formation of Bi 2 O 3 liquid phase [13]. Notably, the pure M-type Sr 1 À x La x Fe 12 À x Co x O 19 hexaferrites are successfully obtained when the La-Co substitution amount x does not exceed 0.3, suggesting that the La 3 þ -Co 2 þ ions partially substitute the Sr 2 þ -Fe 3 þ ions.…”

“…For the polycrystalline permanent magnetic materials, the effective magnetic anisotropy constant K eff can be obtained by the law of approach to saturation (LATS) [13,16]. According to the LATS, the differential susceptibility χ d (dM/dH) is given as…”

“…Interestingly, the K eff and H a gradually increase with increasing substitution amount in the single phase region with x r0.3, denoting that the La 3 þ and Co 2 þ ions have gone into the M-type structure for substituting the Sr 2 þ and Fe 3 þ ions respectively. It is worthwhile to note that the obtained Sr 1 À x La x Fe 12 À x Co x O 19 (x¼ 0.2 and 0.3) ferrites provide relatively high magnetic properties as low temperature sintered M-type hexaferrites for use in microwave LTCC ferrite devices [7][8][9]13], typically including M s above 62 emu/g, H a above 1400 kA/m, and H ci above 320 kA/m.…”

“…Our previous work indicated that the sintering temperature of the SrFe 12 O 19 ferrites prepared by the conventional solid phase method can be reduced to 900°C even much lower by using Bi 2 O 3 as sintering aids [13]. In order to improve their low temperature sintering magnetic properties, the La-Co substituted Sr 1 À x La x Fe 12 À x Co x O 19 (x ¼0-0.5) ferrites with appropriate Bi 2 O 3 additive were further prepared at low sintering temperatures in this work, and the detailed effect of La-Co substitution amount on their crystal structure and magnetic properties was investigated.…”

Electromagnetic wave absorption properties of Ba(CoTi) x Fe12–2x O19@BiFeO3 in hundreds of megahertz band

“…[2] Various EM wave absorption materials with excellent properties have been developed to eliminate the adverse effects of excessive EM radiation on human life. [3][4][5][6] These materials include dielectric materials [7][8][9][10][11] such as carbon materials, [12,13] nonmagnetic sulfides, [14] conjugated polymers [15] and magnetic materials such as ferrites, [16][17][18][19] magnetic metals, [20][21][22] and rare earth alloys. [23,24] However, most studies have mainly focused on EM wave absorption materials in the gigahertz range, whereas studies on absorption materials working in the hundreds of megahertz range are relatively rare.…”