M-type Hexagonal Structure Research Articles

Complex permittivity and complex permeability of Sr ions substituted Ba ferrite at X-band

M-type hexagonal ferrite composition, Ba (1− x )Sr x Fe 12O 19 ( x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), was prepared by a two route ceramic method. Complex permittivity ( ε′− jε″) and complex permeability ( μ′− jμ″) have been measured using a network analyzer from 8.2 to 12.4 GHz X-ray diffraction confirmed the M-type hexagonal structure and a scanned electron micrograph was used to analyze the grain size distribution of ferrite. Substitution of Sr 2+ ions causes an increase in porosity that deteriorates the electromagnetic and microstructural properties in the doped samples. Both dielectric constant and dielectric loss are enhanced in comparison to the permeability and magnetic loss over the entire frequency region. This is due to a resistivity variation and the formation of Fe 2+ ions, which increases the hopping mechanism between Fe 2+ and Fe 3+ ions.

The influence of heat-treatment on microstructure and magnetic properties of rare-earth substituted SrFe12O19

Rare-earth substituted strontium ferrite nanopowders SrFe12−xRxO19 (R = La, Gd and Er; x = 0.2, 0.5 and 1) were prepared by sol–gel-autocombustion method and subsequent heat treatments. The results of X-ray diffraction measurements showed the M-type hexagonal structure. Magnetic properties, such as specific saturation magnetization Ms, specific remanent magnetization σr and coercivity Hc, as well as microstructure depend on the heat-treatment conditions (temperature and time). The coercivity Hc exhibits a great increase after a critical heat-treatment time. This jump of Hc was explained by a transition from the superparamagnetic state to normal state of the single domain nanoparticles. The occurrence of an agglomerated structure composed of magnetically interacting ultrafine crystallites also contributes to the increase of Hc. With increasing R content both the Ms and Mr decrease due to the dissolution of R ions into the hexaferrite lattice.

An investigation of trivalent substituted M-type hexagonal ferrite using X-ray and Mössbauer spectroscopy

Series of substituted M-type hexagonal ferrite has been synthesized, and studied by means of X-ray diffraction, IR and Mossbauer spectroscopy. The samples have the formula (BaCrxFe12−x O19) (with x = 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0). X-ray diffraction studies prove that all samples has a single phase M-type hexagonal structure. The lattice parameters both a and c were found to be composition dependent. This observation was attributed to the atomic radii of the substituted cations. The Mossbauer spectra change from magnetically ordered (x = 0) toward magnetically ordered with strong line broadening. The broadening increases as the Cr content increase. Measurements at low temperature (80 K) restore the magnetic order. The Mossbauer parameters suggest that Cr3+ prefers to occupy the 4f2 and 2a crystal sites. IR absorption bands were observed between 1,500 and 400 cm−1, and confirm the structure in coincidence with X-ray results.

Heat-treatment influence on the microstructure and magnetic properties of rare-earth substituted SrFe12O19

Rare-earth substituted strontium ferrite nanopowders SrFe12-xRxO19 (R = La, Gd and Er; x = 0.2, 0.5 and 1) were prepared by sol-gel-autocombustion method and subsequent heat treatments. Structural and magnetic properties of SrFe12-xRxO19 powders heat treated at 800, 900 and 10000C, for various times, were characterized with an X-ray diffractometer, a vibrating sample magnetometer and a scanning electron microscope. The results of X-ray diffraction measurements showed the M-type hexagonal structure formation by heat treatments. Magnetic properties, such as specific saturation magnetization σs, specific remanent magnetization σr and coercivity Hc, as well as microstructure depend on the heat treatment conditions (temperature and time). The coercivity Hc exhibits a great increase after a critical heat treatment time. When the heat treatment time increases, one obtains an increase in Hc after a shorter heat treatment time. This jump of Hc was explained by a transition from the superparamagnetic state to normal state of the single domain nanoparticles. The occurrence of an agglomerated structure composed of magnetically interacting ultrafine crystallites also contributes to the increase of Hc.The heat treatment determines a reduced grain growth due to the internal stress generated by R ions. With increasing R content the σs and σr decrease due to the dissolution of R ions into the hexaferrite lattice. We believe that by selecting the time and temperature of the heat treatment, microstructure and magnetic properties suitable for magnetic recording media application can be obtained. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of doping MnO 2 on magnetic properties for M-type barium ferrite

The crystalline structure and magnetic properties of M-type barium ferrite doped with small amounts of MnO 2 (0, 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 wt%, respectively) have been investigated by means of XRD, SEM and VSM. The results show that the crystalline structures of barium ferrite are still M-type hexagonal structure and Mn ions are distributed homogeneously in both the grains and the grain boundaries. The saturation magnetization and magnetocrystalline anisotropy constants both reach the highest values when x=0.75 wt%. The displacement of Fe ions from 4f 1 to 2b site is mainly responsible for the appearance of the maximum values.

Mössbauer studies of La–Zn substitution effect in strontium ferrite nanoparticles

Many studies on cation substitution have been carried out in sintered magnets application, since intrinsic magnetic properties such as saturation magnetization depend on the cation configuration in the M-type hexagonal structure. La–Zn substituted Sr-ferrite nanoparticles were fabricated by a sol–gel method. Their magnetic and structural properties were characterized by using the XRD, VSM, TG/DTA, and Mössbauer spectroscopy. We focused on the Mössbauer effects of non-magnetic ions such as the Zn occupation of 4f1 and 2b sites in the M-type hexagonal structure. As substitution x increased, the saturation magnetization increased, and took a maximum at x=0.2 before decreasing again. We interpret that it is closely related to Zn occupation of 4f1 and 2b. This was thought to be caused by the preferential location of Zn2+ at the down-spin Fe3+ site.

High magnetic performance in Al‐substituted BaFe 12 O 19 by a wet chemical process

A wet chemical process has prepared Al-substituted barium ferrite nanoparticles BaFe11AlO19. Structural and magnetic properties of BaFe11AlO19 powers were characterized with an X-ray diffractometer, a vibrating sample magnetometer, and a Mössbauer spectroscopy. The results of X-ray diffraction measurements showed that the BaFe11AlO19 had an M-type hexagonal structure with lattice parameters a0=5.871, c0=23.190 Å and X-ray density ρx=5.194 g/cm3. The particle size was 37 nm. Mössbauer spectra of BaFe11AlO19 measured at various absorber temperatures of 15–800 K. Its Curie temperature is found to be 700 ± 5 K. The average hyperfine field Hhf(T) of the BaFe11AlO19 shows a temperature dependence of [Hhf(T)-Hhf(0)]/Hhf(0)=-0.34(T/TC)5/2-0.05(T/TC)3/2 for T/TC<0.7, indicative of spin-wave excitation. The anisotropy fields HA was 21.2 kOe and anisotropy constant K1 was 2.86 × 106 erg/cm3 at room temperature, as determined the law of approach to saturation (LAS). The saturation magnetization was 44.3 emu/g and the coercivity was 7.56 kOe. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

졸겔법에 의한 Ba-ferrite분말의 제조 및 자기적 특성 연구

BaFe<TEX>$_{12}$</TEX> O<TEX>$_{19}$</TEX> 분말을 sol-gel법을 이용하여 제조하였다. X-선 회절분석결과 hexagonal 결정구조를 갖으며 격자상수 a와 c는 a=5.822, c=23.215 <TEX>$\AA$</TEX>으로 분석되었다 뫼스바우어 분광기 실험을 통해 Curie온도는 780<TEX>$\pm$</TEX>3K 임을 확인할 수 있었으며, 4f<TEX>$_2$</TEX>, 2a. 4f<TEX>$_1$</TEX>, 12k, 2b의 5-site에 해당하는 각각의 이성질체이동값이 상온에서 0.26, 0.24, 0.15, 0.25, 0.24 mm/s로서 Fe<TEX>$^{3+}$</TEX> 의 상태로 존재함을 알 수 있었다. 접근의 법칙(Law of approach to saturation)에 의해 결정자기 이방성 에너지 H<TEX>$_{A}$</TEX> 와 결정자기 이방성 상수 <TEX>$K_1$</TEX>를 계산하였으며 95<TEX>$0^{\circ}C$</TEX>에서 열처리한 바륨페라이트의 경우 <TEX>$K_1$</TEX> = 2.5 <TEX>${\times}$</TEX> <TEX>$10^{6}erg/cm^3$</TEX> 그리고 H<TEX>$_{A}$</TEX> = 14 kOe 값을 가졌다. M-type hexagonal BaFe<TEX>$\sub$</TEX>12/O<TEX>$\sub$</TEX>19/ ferrite powder was prepared by sol-gel process. The M-type hexagonal structure with <TEX>${\alpha}$</TEX> = 5.882 and c = 23.215 <TEX>${\AA}$</TEX> and its Curie temperature T<TEX>$\sub$</TEX>C/ was determined 780<TEX>${\pm}$</TEX>3 K. The isomer shifts of ,4f<TEX>$_2$</TEX>, 2a. 4f<TEX>$_1$</TEX>, 12k, and 2b were indicated 0.26, 0.24, 0.15, 0.25, and 0.24 mm/s, therefore, the valence states of the Fe ions were ferric (Fe<TEX>$\^$</TEX>3+/). By the law of approach to saturation (LAS), the effective anisotropy field H<TEX>$\sub$</TEX>A/ and crystalline anisotropy constant K<TEX>$_1$</TEX> were estimated. The value of K<TEX>$_1$</TEX> and H<TEX>$\sub$</TEX>A/ were K<TEX>$_1$</TEX> = 2.5<TEX>${\times}$</TEX>10<TEX>$\^6/erg/cm^3$</TEX> and H<TEX>$\sub$</TEX>A/ = 14 kOe, respectively.

Growth of Nanocrystalline Barium Ferrite Thin Films by Sol-Gel Method

Nanocrystalline Ba-ferrite thin films with particles of 40-60 nm size range have been prepared by a sol-gel method. The crystal structures were measured by XRD. Thermal analysis such as thermogravimetry analysis (TGA) and differential thermal analysis (DTA) were performed on the dried powder obtained from the Ba-ferrite precursor solution. Magnetic properties were measured using a vibrating sample magnetometer (VSM) at a maximum applied field of 15 kOe. The patterns for the sample annealed at temperature above 973 K indexed well on the M-type hexagonal structure with lattice constants a = 5.891 A and c = 23.200 A. BaFe 12 O 19 (BaM) thin film was epitaxially grown on single crystalline sapphire (001) substrate with BaM(00l)/sapphire(001) relation. The full width at half maximum of the rocking curve of the (008) peak is 0.28°. AFM was used to detect the grain size and surface morphology. Surface roughness of the films was between 2 and 4 nm. The perpendicular coercivity H C ⊥ was 4.9 kOe at room temperature under an applied field of 15 kOe annealed at 1023 K for 2 h.

Magnetic properties of water-based sol-gel derived BaFe/sub 12/O/sub 19//SiO/sub 2//Si(100) thin films

Thin films with barium hexaferrite (BaM) layers on thermally oxidized silicon wafers were fabricated by water-based sol-gel method. Polycrystalline BaFe/sub 12/O/sub 19//SiO/sub 2//Si(100) thin films were characterized with Rutherford backscattering, X-ray diffraction, vibrating sample magnetometer, and atomic force microscope as well as Fourier transform infrared spectroscopy (FT-IR). The thin films were annealed at 600-900/spl deg/C in air for 2 hours. The pattern for the sample annealed at a temperature above 650/spl deg/C indexed well on the M-type hexagonal structure and no other phases were detectable. The films were composed of uniformly distributed hexagonal-type grains, with diameters between 400 and 600 /spl Aring/. Surface roughness of the films was between 20 and 40 /spl Aring/. The perpendicular coercivity H/sub C/spl perp// and in-plane one H/sub C/spl par// were 4766 Oe and 4380 Oe, respectively, at room temperature under an applied field of 10 kOe annealed at 650/spl deg/C for 2 hours.

Mössbauer studies of BaFe11.9Mn0.1O19 by a sol–gel method

BaFe 11.9 Mn 0.1 O 19 powders were prepared by a sol–gel method. Magnetic and structural properties of the powders were characterized by Mössbauer spectroscopy, x-ray diffractometry, and vibrating sample magnetometry. X-ray diffraction and Mössbauer measurements showed that the BaFe11.9Mn0.1O19 had an M-type hexagonal structure with a0=5.900 Å and c0=23.219 Å. Mössbauer spectroscopy was performed at various temperatures ranging from 13 to 800 K, and each spectrum for a temperature below the Curie temperature (TC=775±5 K) was fitted with five subspectra of Fe sites in the structure (4fVI, 2a, 4fIV, 12k, and 2b). The area fractions of the subspectra at 13 K were 18.0%, 10.2%, 17.5%, 46.1%, and 8.2%, respectively. The 2b site had a very large quadrupole splitting. The isomer shifts indicated that the valence state of the Fe ions was ferric (Fe3+). The saturation magnetization Ms was 58 emu/g, and coercivity Hc was 5141 Oe at room temperature under an applied field of 15 kOe.

磁性材料 磁気ディスク用Ｂａ及びＳｒフェライト薄膜の作製

Ba and Sr ferrite thin films with M-type magnetoplumbite hexagonal structure have the great advantage available to incorporate the magnetic disk recording layer without surface protective coating due to their highly chemical stability and wear durability. This paper reports the design criteria of thin film disk media, methods of film formation of Ba and Sr ferrite, heating techniques requiredfor crystallization, the investigation of grain size control.

Processing and Characterization of Hexagonal Ferrite Thin Films from Organometallic Compounds

Thin films of BaFe12O19 were deposited on resistor‐grade alumina by a chemical solution processing method involving the hydrolysis of a barium alkoxide and iron carboxylate. Conversion of the deposited organometallic precursor to an amorphous oxide was accomplished by a thermal decomposition/oxidation at 370°C. Subsequent development of the M‐type hexagonal structure was accomplished with postannealing in air at temperatures in excess of 600°C. All films were characterized by scanning electron microscopy, X‐ray diffraction, and magnetic measurements.

A STUDY ON SUBSTUTION OF Fe IN BaFe12O19 BY Mn

In this paper, we studied the substitution of Fe in BaFe12O19 by Mn. The main results are as follows: (1) For polycrystalline materials of composition BaFe12-xMnxO19, the amount of maximum substitution of Mn is x=4, and the valence of Mn ions are mostly 3+. (2) Mn ions enter only 12 k and 2 a sites, and noncolinear spin structure appears with higher content of Mn (3) The saturation magnetization σ, the anisotropy constant k1 and the Curie temperatur Tc decreas with the increase of Mn content. (4) The zero field splitting constant Dh of Mn in M-type hexagonal structure is lower then that in garnet structure.