J.F. Wang

Structural analysis of hydrothermally synthesized Sr1−xSmxFe12O19 hexagonal ferrites

Abstract M-type hexagonal ferrites of composition Sr1−xSmxFe12O19 with x=0, 0.06, 0.11, 0.2 and 0.33 were produced by hydrothermal synthesis. The purity of the samples was investigated by X-ray diffraction and Mossbauer spectrometry. The analyses reveal for all the samples the presence of the hexagonal M-type phase as the main phase, but also the presence of Sm containing secondary phases of the (Sr,Sm)FeO3−δ type. The results of the Mossbauer analysis show that the hyperfine parameters of the M-type phase contribution do not vary with the Sm content, indicating that the Sm content in the M-type phase is very weak. This is in agreement with the fact that no Fe2+ is detected in the spectra. As both anisotropy field and saturation magnetization remain constant, the increase of the coercivity is thus attributed to microstructural changes, in relation with the presence of the Sm containing secondary phases.

A study of the magnetic properties of hydrothermally synthesised Sr hexaferrite with Sm substitution

Abstract Sm doped Sr hexaferrite particles were synthesised hydrothermally. Post-synthesised calcination with the aim of improving the magnetic properties of as-synthesised particles was conducted at temperatures ranging from 900°C to 1150°C for 2xa0h in air. The effects of the Sm/Sr ratio and the calcination temperature on the crystallography, particle morphology and magnetic properties of Sm doped Sr hexaferrite were investigated by an X-ray diffractometer, scanning electron microscope and vibrating sample magnetometer. It was found that, unlike transition metal element substitution, Sm substitution does not decrease the hexaferrite particle size. The intrinsic coercivities of Sm doped Sr hexaferrite are significantly higher than those of Sr hexaferrite. It has been observed that Sm substitution can increase the intrinsic coercivity of Sr hexaferrite without causing any deterioration of the saturation magnetisation and remanence. In the Sm/Sr range 1/8–1/2 inclusively, there is little change in the coercivity but a slight fall in both the magnetisation and the remanence.

Structural and magnetic properties of hydrothermally synthesised Sr1-xNdxFe12O19 hexagonal ferrites

Abstract M-type hexagonal ferrites of composition Sr 1− x Nd x Fe 12 O 19 with x =0, 0.06, 0.08, 0.11, and 0.20 were produced by hydrothermal synthesis. The phase composition of the samples was investigated by X-ray diffraction and Mossbauer spectrometry. The analyses reveal for all the samples the presence of the hexagonal M-type phase as the main phase. However, Nd containing secondary phases of the (Sr,Nd)FeO 3− δ type are also detected. Mossbauer spectrometry indicates that the Nd content in the M-type phase is very weak, as the hyperfine parameters of the M-type phase contribution do not vary with the Nd content. This is in agreement with the fact that both saturation magnetisation and remanence remain almost constant as the Nd content increases. The variations of the coercive field are thus attributed to microstructural changes, in relation with the presence of the Nd containing secondary phases.

A study of Nd-substituted Sr hexaferrite prepared by hydrothermal synthesis

Nd-substituted Sr hexaferrite (Sr/sub 1-x/Nd/sub x/Fe/sub 12/O/sub 19/) plate-like particles were synthesized hydrothermally and then calcined at temperatures ranging from 1100/spl deg/C to 1250/spl deg/C for 2 h in air. The effects of the Nd-Sr ratio and the calcination temperature on the phase stability and magnetic properties were investigated. Nd substitution up to a Nd-Sr ratio of 1/8 increases the coercivity without causing any significant deterioration in either the saturation magnetization or the remanence.

Structural and Mössbauer analyses of ultrafine Sr1−xLaxFe12−xZnxO19 and Sr1−xLaxFe12−xCoxO19 hexagonal ferrites synthesized by chemical co-precipitation

Ultrafine M-type hexagonal ferrites of nominal composition Sr1−xLaxFe12−x ZnxO19 and Sr1−xLaxFe12−xCoxO19 with x = 0, 0.1, 0.2, 0.3 and 0.4 were produced by chemical co-precipitation. The phase make-up of the samples was investigated by x-ray diffraction. The analyses show that the hexagonal M-type phase is the main phase in all the samples. Secondary (La,Sr)FeO3, ZnFe2O4 and CoFe2O4 phases are also detected, indicating that the La, Zn and Co content in the M-type phase is lower than the nominal content. A complete Mossbauer analysis of the substitution effects in the M-type phase was made. The results show that the M-type phase contains La3+ in the same proportion as Zn2+ and La3+ in the same proportion as Co2+, in the La–Zn and La–Co samples, respectively. The evolution with x of the hyperfine parameters of the components used to fit the contribution of the M-type phase have been interpreted consistently in relation to the substitution effects by means of the comparison between the spectra of the La–Zn and La–Co substituted samples. The results show unambiguously that La3+ ions are located in the Sr2+ sites, Zn2+ ions are located in the 4f1 sites and Co2+ ions are located in both 4f2 and 2a sites.

Rare earth substitutions in M-type ferrites

In this paper, the effects of a partial substitution of Sr by either Sm or Nd but also by La in SrFe/sub 12/O/sub 19/ on the fundamental magnetic properties is investigated. Hysteresis loop measurements were performed using a pulsed field magnetometer. The anisotropy fields of the samples was measured using the SPD method.

Ultrafine SrM particles with high coercivity by chemical coprecipitation

Abstract Ultrafine (∼80xa0nm), single domain Sr hexaferrite (SrM) particles with Sm additives were produced by chemical coprecipitation. The effects of the Sm 3+ /Sr 2+ ratio on the crystallography and magnetic properties of Sm doped SrM ultrafine particles have been investigated. A very high coercivity of 528xa0kA/m (6635xa0Oe) with a magnetisation at 1100xa0kA/m of 63.07xa0J/Txa0kg was obtained for the sample of Sm 3+ / Sr 2+ = 1 14 calcined at 850°C for 2xa0h in air.

A study of Nd doped SrM by hydrothermal synthesis

Summary form only given. Substitution of La and/or La-Co into Sr hexaferrite (SrM) has been reported to improve magnetic properties. Meanwhile, we have observed that the substitution of Sm for Sr in SrM produces an improvement in the coercivity similar to that noted for SrM with La additives. In an effort to improve the magnetic properties of SrM with other rare-earth element additives, Nd doped SrM samples with various Nd/sup 3+//Sr/sup 2+/ ratios were prepared by hydrothermal synthesis and subsequently calcined at 1000/spl deg/C to 1250/spl deg/C.