M-type Ferrites Research Articles

M型フェライトとスピネルフェライトを用いた異方性W型フェライトの合成

M型フェライトとスピネルフェライトを用いた異方性W型フェライトの合成

Crystallographic and magnetic properties of Cu2U-type hexaferrite

Abstract We have investigated the synthesis conditions, and the magnetic properties of the Cu 2 U-type hexagonal ferrite, Ba 4 Cu 2 Fe 36 O 60 . The Cu 2 U-type hexaferrite was synthesized at the sintering temperature of 1050 °C with the initial composition of Ba 4.4 Cu 2 Fe 37.6 O 62.8 (Cu 2 U+0.2T-block). The saturation magnetizations at 300 K and 5 K are 46.8 A m 2 /kg and 65.0 A m 2 /kg, respectively. The Curie temperature is 420 °C which is lower than that of the M-type ferrite (450 °C) but higher than that of the Cu 2 Y-type ferrite (320 °C). The amount of the nonmagnetic impurity in this sample is estimated to be about 10 wt% by the electron probe micro analysis. We estimated the expected saturation magnetization to be 65.2 A m 2 /kg, by assuming the model of a Neel-type ferrimagnetic structure and the reduction of magnetization by the 10 wt% nonmagnetic impurity. This is consistent with the observed magnetization of 65.0 A m 2 /kg at 5 K.

The impact of the iron content on the microstructure and magnetic properties of M-type ferrites Sr0.45Ca0.25La0.30FexCo0.25O19

Abstract M-type ferrite Sr 0.45 Ca 0.25 La 0.30 Fe x Co 0.25 O 19 (10.45 ≤ x ≤ 12.25) magnetic powders and magnets were prepared by a conventional ceramic method. Phase components of the magnetic powders were examined by X-ray diffraction. There is only the magnetoplumbite-type phase in magnetic powders with iron content ( x ) ranging from 10.45 to 11.65. When iron content ( x ) ≥ 11.85, hematite (α-Fe 2 O 3 ) phase begins to occur. The morphology of the magnets was investigated by a field emission scanning electron microscopy. The magnets have formed a hexagonal structure and the particles are distributed evenly. Magnetic properties of the magnets and magnetic powders were measured by a permanent magnetic measuring equipment and a vibrating sample magnetometer, respectively. The remanence, intrinsic coercivity, magnetic induction coercivity, and maximum energy product first increase with iron content ( x ) of range 10.45–11.05 and then decrease when iron content ( x ) continues to increase. The magnetic properties at x = 11.05 reach the maximum values.

Microstructure and magnetic properties of La–Cu doped M-type strontium ferrites prepared by ceramic process

M-type hexaferrite Sr1−xLaxFe12−xCuxO19 (0≤x≤0·35) magnetic powders and magnets were prepared by the ceramic process. X-ray diffraction was used to investigate the phase compositions of magnetic powders. The single magnetoplumbite phase is obtained in magnetic powders with x from 0 to 0·35. The morphology of the magnets shows that the hexagonal structure is formed and the particles are distributed evenly. Magnetic properties of the magnets were measured by a permanent magnetic measure equipment. The remanence and maximum energy product for the magnets first increase with x from 0 to 0·20 and then, start to decrease when x continues to increase. Both the intrinsic coercivity and magnetic induction coercivity decrease linearly with the increase of x from 0 to 0·35.

Structure and Magnetic Properties of Ti-Co Co-Cubstituted Barium Hexaferrite

Polycrystalline Ti-Co co-substituted M-type ferrites Ba (TiCo)xFe12-2xO19 (x=0.25,0.5, 0.75, 1.0 ) samples were prepared by the citrate precursor method. The particle structure and morphology of the products were characterized by X-ray powder diffraction (XRD) and Field Emission Scanning Electron Microscope (FE-SEM). The effects of the substitution rate on the magnetic properties of samples were analysed by magnetic measurement with the Vibrating Sample Magnetometer (VSM) of Physical Properties Measurement System (PPMS). The XRD patterns show that only one type of crystalline phase can be detected and the substitution did not change the crystal structure. The SEM micrographs of Ba (TiCo)xFe12-2xO19 calcined at 450 °C for 5h, and then 950°C for 5h show that the M-type ferrite particles were homogeneously shaped and the grain sizes had no obvious differences when the substitution rate changed. The magnetic hysteresis loops illustrate that the coercivity (Hc) decreased rapidly with the increasing of Ti-Co substitution, while the saturation magnetization (Ms) changed slowly.

Integration of Ni-Cu-Zn and Hexagonal Ferrites into LTCC Modules: Cofiring Strategies and Magnetic Properties

We have studied the integration of Ni-Cu-Zn ferrite spinels as well as substituted hexagonal Co2Y-and M-type ferrites into LTCC (Low Temperature Ceramic Co-firing) modules. The cofiring behavior and the magnetic properties of these materials were investigated and evaluated for multilayer applications. Ni-Cu-Zn ferrites exhibit permeabilities of µ=300–500 for operating frequencies in the MHz range. Cu-substituted Y-type ferrites Ba2Co2-x-yZnxCuyFe12O22 in combination with sintering additives display sufficient shrinkage and densification at 900°C. A permeability of µ=10 is observed; however, substituted Co2Y-type ferrites do not exhibit long-term stability at 900°C. Co/Ti-substituted M-type ferrites BaFe12-2yCoyTiyO19 (y=1.2) with planar magneto-crystalline anisotropy exhibit excellent soft magnetic behavior. Using sintering additives, complete densification is reached at 900°C and a permeability of µ=15 and a resonance frequency of larger than 1?GHz are observed. Integration of ferrite multilayer inductor components into LTCC modules using free and constrained cofiring technologies is demonstrated.

Magnetic Properties of Ca-La-Co M-Type Ferrite Sintered Magnets with CaO and SiO2 Inter-Additives

Magnetic Properties of Ca-La-Co M-Type Ferrite Sintered Magnets with CaO and SiO2 Inter-Additives

Microwave magnetic and absorption properties of M-type ferrite BaCoxTixFe12−2xO19 in the Ka band

In this study, microwave magnetic and absorption properties were investigated for BaCoxTixFe12−2xO19 (x=0.3, 0.4 and 0.5). M-type barium ferrite can be used as high frequency absorber by Co–Ti substitution because of the strong uniaxial anisotropy and high saturated magnetization. The X-ray diffraction and magnetic hysteresis loops of the samples show that the c-axis anisotropy of BaCoxTixFe12−2xO19 decreases with the substitution, resulting in the decrease of coercivity. The frequency dependence of complex permeability, permittivity and microwave absorption of BaCoxTixFe12−2xO19 has been studied in the Ka band (26.5–40GHz), respectively. The results show that the natural resonance frequency decreases with the substitution. The complex permeability increases as the sintering temperature increases in the range from 1280°C to 1310°C with 10°C as a step. The imaginary part of permeability value obtained here is the highest value among the reported ferrite millimeter wave absorbers in the Ka band. The microwave absorption bandwidth at −10dB of BaCoxTixFe12−2xO19 is effectively broadened compared with other ferrites. Therefore, BaCoxTixFe12−2xO19 may be a good candidate for electromagnetic materials with low reflectivity in the Ka band.

ChemInform Abstract: Hexagonal Ferrites: A Review of the Synthesis, Properties and Applications of Hexaferrite Ceramics

AbstractReview: 560 refs.

Effect of microwave sintering on microstructural and magnetic properties of strontium hexaferrite using sol–gel technique

The sol–gel method is used to prepared hexaferrite using d-Fructose as a fuel. The effect of sintering temperature on the microstructure of SrFe12O19 ceramics is analyzed. The observed XRD results indicate a well-formed crystalline phase of dense hexagonal SrFe12O19 ceramics. From this analysis, no secondary phases are identified. The microstructure of the sintered single phase M-type ferrites ceramics displays a hexagonal-platelet like morphology. Sintering temperature can markedly affect the grains in sintered ferrite. The sintered product is shown to be dense microstructure with relatively small grains. The maximum sintered density 95 % was obtained at lower temperature of 1,150 °C. In addition, saturation magnetization (50.43 emu/g) and the coercivity (Hc) 5,594.53 Gauss were observed.

Synthesis and Magnetic Property of BaZr(CoMn)0.5Fe10O19 Powder by Coprecipitation Method

Substituted M-type hexaferrites are highly anisotropic ferromagnetic materials. In this paper, we report the synthesis and characterization of BaZr(CoMn)0.5Fe10O19 powder by coprecipitation method. The effects of ethanol in precursor solution and preheating were investigated. The synthesized powders were characterized with X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The experimental results indicated that the powder prepared with the water as solvent exhibit high coercivity of 1.30 kOe and a high saturation magnetization of 38.65 emu g-1, and the powder prepared with the water and ethanol as solvent exhibit low coercivity of 1.01 kOe and a low saturation magnetization of 34.25 emu g-1, at applied field of 30 kOe. The preheating at 400 °C also led to some changes in particle morphology and magnetic property for both powders. The present article discussed the useful patents in the field of application and invention of substituted M-type ferrite.

Influence of Ca substitution on the microstructure and magnetic properties of SrLaCo ferrite

M-type ferrites Sr(0.55−x)CaxLa0.45Fe11.65Co0.35O19 (x=0, 0.05, 0.15, 0.25 and 0.35) were prepared by the ceramic process. Phase composition, morphology and sublattice occupation of the material were characterized by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy, respectively. Magnetic properties of the materials were tested by a vibrating sample magnetometer. The results show that the samples are all composed of single M-type hexagonal ferrite after the Ca substitution, while the lattice constant c decreases and the lattice constant a does not change basically with increase of the substitution amount. In addition, the intrinsic coercive force increases obviously when the Ca substitution amount x<0.25, while the saturation magnetization does not change after Ca addition, which is attributed to the change of the Fe3+ sublattice occupations suggested by Mössbauer spectroscopy.

Cofiring behavior of multilayer inductors based on substituted Y- and M-type hexagonal ferrites

Sinter-active soft ferrites with adequate permeability profiles are required for the fabrication of multilayer ferrite inductors (MLFI). For MLFI fabrication, a Low Temperature Ceramic Co-firing (LTCC) process is used. Substituted hexagonal ferrites of Y-, and M-type represent an important family of soft ferrites which might operate at high-frequency conditions up to 2 GHz. However, for Ag-based multilayer inductor applications a sinter process at 900°C is required. Low-temperature sinter-ability is provided by the use of sub-micron powders and/or sintering additives. Substituted Y-type hexagonal ferrites Ba2Co2-x-yZnxCuyFe12O22 were obtained after sintering at 1000°C. Substitution of Cu for Co improved the low-temperature sintering behavior. The addition of 5wt.% Bi2O3 guarantees almost complete densification at 900°C. The saturation magnetization and permeability are significantly affected by the Zn-concentration. A maximum permeability of μ′ = 10 and cut-off frequency fg~2GHz was observed for a ferrite with y = 0.4. Co/Ti-substituted M-type BaFe12-2yCoyTiyO19 ferrites can also be used for multilayer inductors. The magneto-crystalline anisotropy changes from uniaxial to planar upon Co/Ti-substitution, and ferrites with y≥1.1 exhibit soft magnetic behavior. Ferrite powders were prepared at 1000°C. The addition of a sintering aid shifts the temperature of maximum shrinkage down to below 900°C and dense samples were obtained after firing at 900°C. A permeability of μ′ = 16 and a resonance frequency of 1 GHz was observed. Substituted M-type ferrites are stable during co-firing at 900°C and show no sign of decomposition, i.e. these materials are LTCC-compatible. Ferrite tapes were prepared by tape casting and multilayer structures were fabricated by screen printing, stacking, lamination and final co-firing. Firing was performed at LTCC conditions i.e. 900°C. We report on the co-firing behavior, microstructure and permeability of monolithic laminates. It is shown, that hexagonal Co2/Zn2Y- and Co/Ti-M-type ferrites are excellent magnetic materials for multilayer inductors.

Effect of La Doping on Structural and Magnetic Properties of SrLa&lt;sub&gt;x&lt;/sub&gt;Fe&lt;sub&gt;12−x&lt;/sub&gt;O&lt;sub&gt;19&lt;/sub&gt; Ceramics from Aqueous Solution Method

Influences of different amount of La-substituted on structural and magnetic properties of M-type strontium ferrites SrLaxFe(12−x)O19 compounds prepared by an aqueous solution method have been systematically investigated by XRD, VSM and TEM. In this work, it is found that only magnetoplumbite structure exists in the sample rather minorphases from the XRD patterns. When the doping content is x≤0.06mol, substituting of La3+ for Fe3+ occurs, forming SrLaxFe(12-x)O19. In contrast, when the doping content is x&gt;0.06mol, Sr2+ is substituted by La3+, forming Sr(1-x)LaxFe12O19. The saturation magnetization (σs) shows its maximum at x=0.04 while the peak value of the intrinsic coercive field (Hjc) presented at x=0.06 as the La substituted content increases. The obtained results also indicated that the shape of the formed SrLaxFe(12−x)O19 is oblong with 70nm length and 40nm width.

Low-Temperature Firing of Substituted M-Type Hexagonal Ferrites for Multilayer Inductors

Co/Ti-substituted M-type BaFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12-2x</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ti <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> ferrites were investigated for multilayer inductor applications. Single-phase ferrite powders were prepared at 1000°C through the mixed oxide route. After sintering at 1300°C a maximum permeability of μ' = 37 is observed for x = 1.2. The addition of a glass sintering aid shifts the temperature of maximum shrinkage down to below 900°C and dense samples were obtained after firing at 900°C. For ferrites with x = 1.2 a permeability of μ' = 13 and a resonance frequency of 1 GHz is observed. Contrary to substituted Zand Y-type hexagonal ferrites, the Co/Ti-substituted M-type ferrites are stable during co-firing at 900°C and show no sign of thermal decomposition, i.e., these materials are compatible with the low-temperature ceramic cofiring (LTCC) technology. It is shown that Co/Ti-M-type ferrites are excellent magnetic materials for multilayer inductors.

Magneto-optical Kerr spectra and magnetic properties of Co-substituted M-type strontium ferrites

M-type strontium ferrites SrFe12−xCoxO19 (x=0, 0.05, 0.10, 0.15, 0.20) were prepared by the conventional ceramic technology. The structure, magnetic properties and magneto-optical Kerr activity of the samples were investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and magneto-optical ellipsometry, respectively. X-ray diffraction showed that all the samples were single phase ferrites. The magnetic properties, especially the coercive field, were remarkably modified due to the substitution of cobalt. Most importantly, a noticeable Kerr activity was demonstrated in the Co-substituted M-type strontium ferrites with x=0.20.

CTAB-assisted low-temperature synthesis of SrFe12O19 ultrathin hexagonal platelets and its formation mechanism

Single domain particles (50–150nm) of the M-type strontium ferrite (SrFe12O19) were synthesized via co-precipitation method using cetyltrimethyl ammonium bromide (CTAB) as a surfactant, followed by heat treatment at 900°C for 2h. The effects of CTAB contents (x=0, 1, 3, 6, 9wt.%) on formation, structure, morphology and magnetic properties of the strontium hexaferrite particles were investigated. Single phase M-type ferrite powders with ultrathin hexagonal platelet-like (thickness: 10–20nm) morphology were obtained in the existence of CTAB surfactant, whereas secondary phase α-Fe2O3 was detected in the samples prepared without CTAB, exhibiting rod-like shape. Both the saturation magnetization and coercivity increased with CTAB content up to x=6wt.% and the optimal values were 68.7emu/g and 6620Oe, respectively. These results implied that CTAB may act as a crystallization master, controlling the nucleation and growth of the crystals. Two distinct formation mechanisms have been proposed to explain the different SrFe12O19 particle morphologies. These nanoparticles are promising for the building blocks of hard magnets and magnetic recordings.

Preparation and Magnetic Properties of La-Co Co-Doped M-Type Strontium Ferrite Nanofibres

Polyethylene pyrrole(PVP)and metal nitrate were used as precursors,La and Co co-doped M-type strontium ferrites Sr 1-x La x Fe 12-x Co x O 19 (x=0.12)(SLFC)were prepared by electrospinning,sol-gel, and subsequent heat treatment processing.The crystal structure,morphology,and magnetic properties of the samples were studied by means of X-ray diffraction(XRD),scanning electron microscopy(SEM), transmission electron microscopy(TEM),and superconducting quantum interference device(SQUID).The influences of the variation of sintering temperature on the magnetic properties of SLFC were systematically investigated.The experimental results show that the optimum values of the magnetic properties were obtained at 950°C for 2 h,and the coercivity(H c ),saturation magnetization(M s ),and remanence(M r )values of the samples were 498.53 kA·m -1 ,70.76 A·m 2 ·kg -1 ,and 36.35 A·m 2 ·kg -1 , respectively.Pure-phase bamboo-like SLFC nanofibres with diameter of about 55 nm were fabricated. The magnetic properties of undoped SrFe 12 O 19 (SF)were improved obviously,and the SF nanofibres exhibited better magnetic properties than the corresponding nanoparticles obtained by the sol-gel processing.

Z-, Y- and M-type Hexagonal Ferrites for High-Frequency Inductive Multilayer Devices

Hexagonal ferrites can be used as soft magnetic materials for multilayer inductors for high frequency applications up to 3 GHz. We report on the preparation, thermal stability and magnetic properties of Z-, Y- and M-type hexagonal ferrites. Co2Z-type ferrite Ba3Co2Fe24O41 and iron excess Ba3Co2−yFe24+yO41 (0 ≤ y ≤ 0.8) were prepared by the mixed oxide route. Single phase Z-type ferrites were obtained after sintering at 1300°C. The permeability of a sample with y = 0.6 sintered at 1300°C is μ = 30 with a resonance frequency of 1 GHz. The addition of Bi2O3 as sintering aid shifts the maximum shrinkage down to 950°C and dense samples were sintered at 950°C; however, their permeability is only μ = 3…5. It is shown that Co2Z ferrites are not stable under LTCC conditions. Cu-substituted Z-type ferrites Ba3Co2-xCuxFe24O41 exhibit enhanced sintering ability, but sintering at 950°C also results in low permeability. Y-type hexagonal ferrites Ba2Co2−x−yZnxCuyFe12O22 were prepared at 1100°C and a permeability of μ = 20 was found for x = 1.2 and y = 0.8. Samples with Bi2O3 addition were sintered at 950 and 900°C exhibiting a permeability of μ = 10. Similar values were measured for M-type ferrites BaFe12-2yCoyTiyO19 with y = 1.2 which were sintered at 900°C using additives. Co/Ti co-substitution is an essential prerequisite for tailoring the magneto-crystalline anisotropy. Co/Ti- substituted M-type materials are stable under LTCC conditions. Ferrite multilayer devices were fabricated by screen printing coils onto ferrite tapes, stacking and lamination. Firing was performed between 1300°C and 900°C, i.e. at HTCC and LTCC conditions, respectively. The inductance behavior of the devices was evaluated and modeled. It is shown that hexagonal ferrites are suitable materials for the high-frequency multilayer inductors; however, Y- and M-type ferrites are preferred for LTCC-type inductors cofired at 900°C with Ag metallization.

Preparation of nanophase M-type ferrite and its laser-attenuated characteristics

By citrate sol-gel auto-combustion method, the nanophase M-type planar hexagonal ferrite is prepared. The transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermal analysis are used to study the grain size, phase composition, microstructure and crystallization process. The results show that the nanophase M-type Sr-ferrite prepared by this method is single, and its grain size is smaller than 100 nm. Moreover, most of the grains present hexagonal sheet shape. Tests are carried out for its attenuation to 1.06 μm laser. It is found that the extinction capability of the nanophase M-type Sr-ferrite smoke is good, and its mass extinction coefficient is 1.628 m2/g.