SrFe12O19 Ferrites Research Articles

Effects of La–Zn substituent and calcination temperature on the microstructure and magnetic properties of Sr-ferrites

Abstract In this study, La–Zn-substituted SrFe12O19 ferrites were synthesized using the traditional ceramic process. The by-products of iron oxide scales from a steel plant were used as the main raw materials. The influence of the La–Zn substituent and the calcination temperature on the microstructure and magnetic properties of Sr1 − x La x Fe12 − x Zn x O19 ferrites was investigated. The results showed that with the increase in the x value, the crystalline lattice constant of the a- and c-axes and the cell volume decreased. There was no α-Fe2O3 phase in the ferrites when the value of x was 0.3. The corresponding saturation magnetization (M s) and remnant magnetization (M r) values were, respectively, about 65 emu g− 1 and 39.5 emu g− 1. Both values of M s and M r rise to the maximum value. When the calcination temperature was reduced from 1200°C to 1150°C, the average particle size decreased from 0.9 μm to 0.7 μm and M s remained at 65 emu g− 1. However, the coercivity increased from 2690 Oe to 3100 Oe.

Preparation and Magnetic Properties of SrFe12O19 Ferrites Suitable for Use in Self-Biased LTCC Circulators

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 Keff 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.

Obtainment of exchange coupling coefficient of Ni0.6Zn0.4Fe2O4/SrFe12O19 composites

By controlling the phase distribution and interfacial conditions, the composites of (soft)Ni0.6Zn0.4Fe2O4/(hard) SrFe12O19 ferrites were prepared with different mass ratios fs of soft magnet. The coercivity mechanism was analyzed according to the theory for melt-spun and sintered magnets. Using the modified Brown׳s equation, we derive the exchange coupling coefficient αex that can be quantificationally expressed as αex=α0exp(−fs/f0) with α0 and f0 being constants, which has not been reported before as far as we know.

Crystal structure and magnetic properties of Sr1 − x Sm x Fe12 − x Co x O19 solid solutions

Sr1 − x Sm x Fe12 − x Co x O19 (0 ≤ x ≤ 0.5) ferrites have been prepared by solid-state reactions in air at 1470 K using mixtures of samarium oxide, ferric oxide, Co3O4, and strontium carbonate. X-ray diffraction characterization showed that the samples with x < 0.2 were single-phase, whereas the samples with 0.2 ≤ x ≤ 0.5 contained α-Fe2O3 and those with 0.3 ≤ x ≤ 0.5 contained SmFeO3, CoFe2O4, and Sm2O3 as well. The highest degree of Sm3+ and Co2+ substitutions for Sr2+ and Fe3+ (x) in the SrFe12O19 ferrite at 1470 K was determined to be slightly less than 0.2. This substitution only slightly decreases the a and c parameters of the hexagonal lattice and the Curie temperature (T C) of the material. At temperatures of 5 and 300 K in magnetic fields of up to 14 T, we obtained magnetic hysteresis loops, which were used to evaluate the spontaneous magnetization (σ0), specific saturation magnetization (σs), and coercive force (σ H c) of the ferrites. The experimentally determined 5-K spontaneous magnetization per formula unit (n 0) of the x = 0.1 ferrite is 20.86μB, which coincides with the theoretical value calculated as n 0 = (8 × 5) − (3.9 × 5 − 0.1 × 3) = 20.8μB. At 300 K, the n 0 and σ H c of Sr0.9Sm0.1Fe11.9Co0.1O19 exceed those of SrFe12O19 by 7.7 and 9.9%, respectively.

Effect of Swift Heavy Ion Irradiation on Structural and Magnetic Properties of Strontium Hexaferrites

Swift heavy ion irradiation of material is a unique tool to modify the properties of the material and it provides an alternative to photons for introducing electronic excitations into the material. In the present investigation, the changes in structural, morphological and magnetic properties of SrFe12O19 ferrite (prepared using co-precipitation and SHS routes), induced by 200 MeV Ag+16 ion irradiation have been studied. In order to study the effect of the electronic stopping power (dE/dX) e on these properties the energy of the projectile was so chosen that it could easily pass through the samples. Structural properties of these ferrites have been studied and compared with the properties after Swift Heavy Ion (SHI) irradiation of 200 MeV Ag16+ at different fluences. Samples were characterized using different experimental techniques, like Fourier Transform Infra-red (FT-IR), X-ray Diffraction (XRD), Scanning Electrom Microscope (SEM), Vibrating Sample Magnetometer (VSM) and LCR meter. FTIR spectra for pristine as well as the irradiated samples were recorded for wave number ranges from 4000-400 cm-1 using the KBr pellet method. FTIR measurement of the bonds' vibration modes in all samples were carried out to determine the change in MO bonding due to irradiation. The MO absorption band is observed in all samples. The intensity of absorption bands increased in irradiated samples, which confirms the formation of strong ferric oxide band. Crystallinity of pristine and irradiated samples was investigated by XRD technique. All XRD peaks were indexed using POWDER X software. XRD result confirms the formation of mono phase. It is observed from XRD analysis that after the irradiation, the intensity of all the peaks and FWHM were increased. There is no significant change in peak position but the intensity is decreased and FWHM is increased continuously with ion fluence. XRD patterns confirm that the ferrite structure is retained even after irradiation. Surface morphology of pristine and irradiated samples was studied using a scanning electron microscopy. It is observed from SEM images that the particle size decreases after irradiation and particles become more homogeneous. Dielectric and magnetic measurements were also carried out.

Hexagonal SrFe12O19 ferrites: Hydrothermal synthesis and their sintering properties

Hexagonal M type SrFe12O19 (SrM) ferrites were synthesized by the hydrothermal method, and the effects of molar ratio of OH−/NO3− (RO/N), the atomic ratio of Fe/Sr (RF/S) and sintering on the phase composition and magnetic properties of as-synthesized specimens are studied. It is found that the RO/N and RF/S in starting materials affect the phase composition and magnetic properties greatly. Fe2O3 is found as impurity in some specimens, while in all as-synthesized specimens, SrCO3 forms inevitably during the synthesis process. After sintering at 1100°C, the perovskite type SrFeO3−x ferrite forms as the product of SrCO3 and Fe2O3 at high temperature, and the specimens exhibit the Perminvar magnetic hysteresis loops which show two-phase magnetic behaviors. However, when sintered at 1200°C, SrFeO3−x further reacts with Fe2O3 to produce SrFe12O19, and the specimens with RF/S=8, 9 and 10 exhibit the single-phase hexagonal structure and magnetic behavior. It is also found that the saturation magnetization and coercivity are both enhanced after sintering at high temperatures due to the elimination of impurities.

One-Dimensional SrFe&lt;SUB&gt;12&lt;/SUB&gt;O&lt;SUB&gt;19&lt;/SUB&gt;/Ni&lt;SUB&gt;0.5&lt;/SUB&gt;Zn&lt;SUB&gt;0.5&lt;/SUB&gt;Fe&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;4&lt;/SUB&gt; Composite Ferrite Nanofibers and Enhancement Magnetic Property

SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers of diameters about 100 nm with mass ratio 1:1 have been prepared by the electrospinning and calcination process. The SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrites are formed after calcined at 700 degrees C for 2 hours. The composite ferrite nanofibers are fabricated from nanosized Ni(0.5)Zn(0.5)Fe2O4 and SrFe12O19 ferrite grains with a uniform phase distribution. The ferrite grain size increases from about 11 to 36 nm for Ni(0.5)Zn(0.5)Fe12O4 and 24 to 56 nm for SrFe12O19 with the calcination temperature increasing from 700 to 1100 degrees C. With the ferrite grain size increasing, the coercivity (Hc) and remanence (Mr) for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers initially increase, reaching a maximum value of 118.4 kA/m and 31.5 Am2/kg at the grain size about 40 nm (SrFe12O19) and 24 nm (Ni(0.5)Zn(0.5)Fe2O4) respectively, and then show a reduction tendency with a further increase of the ferrite grain size. The specific saturation magnetization (Msh) of 63.2 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers obtained at 900 degrees C for 2 hours locates between that for the single SrFe12O19 ferrite (48.5 Am2/kg) and the single Ni(0.5)Zn(0.5)Fe2O4 ferrite (69.3 Am2/kg). In particular, the Mr value 31.5 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers is much higher than that for the individual SrFe12O19 (25.9 Am2/kg) and Ni(0.5)Zn(0.5)Fe2O4 ferrite (11.2 Am2/kg). These enhanced magnetic properties for the composite ferrite nanofibers can be attributed to the exchange-coupling interaction in the composite.

Crystal structure and magnetic properties of high-coercivity Sr1 − x Pr x Fe12 − x Zn x O19 solid solutions

Sr1−x Pr x Fe12 − x Zn x O19 ferrites with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 have been prepared by solid-state reactions between praseodymium, iron, and zinc oxides and strontium carbonate in air at 1470 K. According to X-ray diffraction results, the samples with x ≤ 0.2 were single-phase and those with 0.3 ≤ x ≤ 0.5 contained, in addition to the magnetoplumbite phase, small amounts of α-Fe2O3, ZnFe2O4, and PrFeO3. The mixed-phase samples further fired twice at 1470 K for 4 and 2 h contained no impurity phases at x = 0.3 and contained only α-Fe2O3 at x = 0.4 and 0.5. In the composition range 0 ≤ x ≤ 0.3, the a and c cell parameters, unit-cell volume V, and X-ray density ρx of the magnetoplumbite phase vary linearly according to the relations a(A) = 5.8869 − 0.0162x, c(A) = 23.027 + 0.449 x, V(A3)= 691.10 + 9.65x, and ρx(g/cm3) = 5.102 + 0.230 x. The highest degree of combined heterovalent substitution of Pr3+ for Sr2+ and Zn2+ for Fe3+ in the SrFe12O19 ferrite (formation of Sr1−x Pr x Fe12 − x Zn x O19 solid solutions) at 1470 K is x = 0.32−0.36. The saturation magnetization per formula unit (n s) of the x = 0.1 ferrite exceeds that of SrFe12O19 by 1.7% at 6 K and by 15.2% at 308 K. The 308-K n s and coercive force (σ H c) of the x = 0.2 ferrite exceed those of SrFe12O19 by 7.6 and 8.5%, respectively.

Synthesis, Characterization, and Microwave Absorption Properties of SrFe&lt;sub&gt;12&lt;/sub&gt;O&lt;sub&gt;19&lt;/sub&gt; Ferrites and FeNi&lt;sub&gt;3&lt;/sub&gt; Nanoplatelets Composites

M-typical SrFe12O19 ferrites and FeNi3 nanoplatelets were successfully prepared by the sol-gel method and solution phase reduction method, respectively. The crystalline and morphology of particles were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The composite coatings with SrFe12O19 ferrites and FeNi3 nanoplatelets in polyvinylchloride matrix were prepared. The microwave absorption properties of these coatings were investigated in 2-18GHz frequency range. The results showed that the M-typical SrFe12O19 ferrites and FeNi3 nanoplatelets were obtained and they presented irregular sheet shapes. With the increase of the coating thickness, the absorbing peak value moves to the lower frequency. The absorbing peak values of the wave increase along with the increasing of the content of FeNi3 nanoplatelets filling fraction. When 40% SrFe12O19 ferrites is doped with 20% mass fraction FeNi3 nanoplatelets to prepare composite with 1.5mm thickness, the maximum reflection loss is -24.8 dB at 7.9GHz and the -10 dB bandwidth reaches 3.2GHz.

Effect of forms of B2O3-SiO2 as an additive on magnetic properties of SrFe12O19 ferrites

Strontium ferrites (SrO · 5.5Fe2O3) were prepared using hot-rolled mill scale as a source of iron oxides. Calcination was performed at 1200°C for 2 h. The fused B2O3-SiO2, with various mole ratios of B2O3 to SiO2, was added to the calcined ferrites during the milling stage. The ferrites were formed anisotropically. The fused additives are quite effective to enhance the magnetic properties; (BH)max can reach 3.0 MGOe for the ferrite sintered at 1220°C for 2 h. In general, (BH)max is independent of the mole ratio of B2O3 to SiO2 and dominantly influenced by the sintering temperature. The addition of 0.3 or 0.5 wt% fused additives showed no significant difference in the magnet quality. The quality of the magnet was decreased with increasing mole ratio of B2O3 to SiO2 when unfused B2O3-SiO2 was used under the same processing conditions.