M-type Phase Research Articles

Study on preparation and magnetic properties of Sr1-xGdxFe12-xCuxO19 (0.00 ≤ x ≤ 0.20) strontium ferrite prepared by solid phase method

ABSTRACTM-type strontium ferrites (Sr1-xGdxFe12-xCuxO19, x = 0.00, 0.05, 0.10, 0.15 and 0.20) doped with equivalent ions were synthesized via the solid phase method. The crystallographic structure, morphology and magnetic properties of samples were investigated using x-ray diffractometry (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM), respectively. The XRD results show that the pure M-type phase is successfully obtained when the Gd–Cu substitution amount x below 0.20. When the doping content is low, the typical hexagonal block structure appears in the magnet. When x is 0.05, the saturation magnetization (Ms), remanent magnetism (Mr) and coercivity (Hc) reach the maximum values of 51.25 emu/g, 565.50 Oe and 27.67 emu/g, respectively.

Investigating the influence of Cr-Zn substitution on magnetic and structural properties of M-type SrBaSm hexaferrites Sr0.6Ba0.1Sm0.3Fe12.0-x(Cr0.6Zn0.4)xO19

The Cr-Zn substituted M-type SrBaSm hexaferrites Sr0.6Ba0.1Sm0.3Fe12.0-x(Cr0.6Zn0.4)xO19 (0.00 ≤ x ≤ 0.75) were synthesized by the conventional ceramic route. The crystal structures were identified by X-ray diffraction. XRD analysis showed that the magnetic powders with CrZn content (x) from 0.00 to 0.30 had M-type as major phase and α-Fe2O3 as impurity phase, while the magnetic powders with CrZn content (x) ≥ 0.45 exhibited a single M-type phase. The grain morphology of the magnets was observed by a field emission scanning electron microscopy (FE-SEM). The FE-SEM images show that all grains were distributed homogeneously and had regular hexagonal platelet-like shape. The magnetic properties of the magnets were derived from the demagnetizing curves. The remanence (Br) and maximum energy product [(BH)max] first increased with increasing CrZn content (x) from 0.00 to 0.30, and then decreased when CrZn content (x) ≥ 0.30. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first decreased with increasing CrZn content (x) from 0.00 to 0.30, and then slightly fluctuated and basically remained unchanged when CrZn content (x) ≥ 0.30.

Microstructure and properties of the Ba0.75−xCaxLa0.25Fe11.6Co0.25Ti0.15O19 hexaferrites

In the case of Ti4+ remain unchanged, the Ca2+ substituted Ba0.75−xCaxLa0.25Fe11.6Co0.25Ti0.15O19 (0 ≤ x ≤ 0.05) were prepared by conventional solid-state reaction method at temperature of 1280 °C. A ball-to-power weight ratio of 10:1. Their crystal structure and magnetic properties were mainly investigated. The results show that the single magnetoplumbite phase structure transformed into the multiphase structure. Meanwhile, the small amount of α-Fe2O3 phase existed in M-type phase. The micrographs were observed by a field emission scanning electron microscopy (SEM). Vibrating sample magnetometer (VSM) was used to analyze the magnetic properties. The saturation magnetization (M s ) first increases then decreases when x from 0 to 0.03. But, when x from 0.03 to 0.05, the saturation magnetization (M s ) first increases then decreases too. The maximum value is at x = 0.04 (M s = 70.73 emu/g). The value of coercivity (H c ) first increases then decreases when x from 0 to 0.04. But, the value increased when x from 0.04 to 0.05. The maximum value is at x = 0.02 (H c = 1691 Oe).

Magnetic, electrical and dielectric properties of microwave sintered Sr1−x La x Fe12−x Ni x O19 (x = 0−0.35) hexaferrites used for nonreciprocal LTCF devices

The Sr1−x La x Fe12−x Ni x O19 (x = 0−0.35) hexaferrites with 3 wt% Bi2O3 additive were prepared by microwave sintering method at 870 °C. Crystal structure, microstructure, magnetic, electrical, and dielectric properties of these low temperature sintered ferrites were investigated. The results show that the pure M-type phase is obtained for the ferrites with 0≤ x ≤0.25. With further increasing substitution amount, the multiphase structure is inevitably formed, and the LaFeO3 phase coexists with the M-type phase. In single M-type phase region, the variation of magnetic properties with La3+–Ni2+ substitution amount can be well explained based on the occupancy effects of La3+ and Ni2+ in magnetoplumbite structure. Besides, the electrical transport and polarization behaviors of the ferrites are clearly discussed. It suggests that the appropriate La3+–Ni2+ substitution (x = 0.2) improves their intrinsic magnetic and electrical properties for applying in nonreciprocal low temperature co-fired ferrite (LTCF) devices.

Effect of M-Type Hexaferrites on Mechanical and Magnetic Properties of Hydroxyapatite Ceramics

The overall aim of this study is to establish the inter-relationships between phase formations, mechanical properties and magnetic properties of the novel ceramic in hydroxyapatite system for biomaterial applications. First, barium hexaferrite and strontium hexaferrite powders were prepared as M-type hexaferrite phases. Hydroxyapatite was prepared from cockle shells via co-precipitation method. After that, a combination between hydroxyapatite+barium hexaferrite and hydroxyapatite+strontium hexaferrite was mixed together then shaping and sintering at 1200 °C for 2 h. The sintered samples were characterized phase formation, mechanical and magnetic properties by using X-ray diffraction (XRD), Universal testing and VSM measurements, respectively. XRD patterns for all samples showed a combination between hydroxyapatite and hexaferrite phases. Compressive strength of all samples tends to increase with increasing of the amount of hexaferrite phases due to densification mechanism. However, the increasing of these values, it appears that there is no difference in the statistical significant. For magnetic properties, the coexistence of barium hexaferrite and strontium hexaferrite phases reveals magnetic hysteresis loops, showing the change from diamagnetic to ferromagnetic behavior.

Synthesis, structure, and magnetic properties of M-W hexaferrite composites

Abstract Ca-Co-Mn-Zn-doped Sr-hexaferrites with a cation composition of Sr 0.7 Ca 0.3 Fe n-0.6 Co 0.2 Mn 0.2 Zn 0.2 were prepared using conventional solid-state reaction processes by varying Fe contents (10 ≤ n ≤ 17). The hexaferrite sample with an Fe content of 10 ≤ n ≤ 13 exhibited composite phases of M-type and W-type hexaferrite on calcining at 1250 °C in air while the samples calcined at 1200 °C in air exhibited only the M-type phase. The sample with n = 13 exhibited a saturation magnetization ( M S ) of 70.7, 75.3, 78.0 emu/g after performing calcination at 1200, 1250, and 1300 °C, respectively. M S higher than that of the non-doped M-type Sr-hexaferrite (~ 72 emu/g) sample is attributed to the volume portion of the high- M S W-type phase. It is also revealed that the co-doping of Ca, Co, and Zn is crucial for the formation of the W-type phase in the sample calcined at 1250 °C in air.

Phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc2O3⋅5.1Fe2O3

The phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc2O3⋅5.1Fe2O3 have been investigated. Results show that when the calcination temperature is lower than 1000 °C, the spinel phase BaFe2O4 and M-type hexaferrite phase BaFe12O19 dominate. The M-type hexaferrite BaFe12−xScxO19 (0 < x ≤ 1.8) appears above 1050 °C and becomes a single phase BaFe10.2Sc1.8O19 above 1200 °C. A two-step decrease of both the coercivity and remanence ratio is observed above 1050 °C, which agrees well with the appearance of soft magnetic phase BaFe12−xScxO19 (0 < x ≤ 1.8). The saturation magnetization of the sample increases with calcination temperature until 1100 °C and then decreases. Raman spectra results show that the above magnetic property evolutions can be explained by a temperature dependent incorporation of Sc3+ into the lattice sites nearby the magnetic blocks’ interfaces. This weakens the local magnetic exchange interactions between Fe3+ and thus leads to a change in the magnetic structure.

Structural and magnetic properties of BaFe12−2xCuxMnxO19 hexaferrites

In this study, ball-milling method was adopted for the synthesis BaM-hexaferrites BaFe12−2xCuxMnxO19 (x = 0.00, 0.25, 0.50, 0.75, and 1.00). The system shows pure BaM phase in the samples with x = 0.0 and x = 0.25. At higher substituent concentrations, Y-type hexaferrite phase developed. The evolution of the Y-type phase was confirmed by Rietveld refinement of the x-ray diffraction patterns, and the thermomagnetic measurements from which the Curie temperature of the existing phases was determined. The Curie temperature for the M-type phase decreased with increasing x, signaling the reduction of the superexchange interaction strength. The particle size of the pure sample was within the critical single-domain size, and the size increased with increasing x as determined by SEM imaging. These variations induced significant reduction in the coercivity as a consequence of the development of multi-domain particles with increasing x. The coercivity decreased from 3.4 kOe for the pure sample, down to 50 Oe for the sample with x = 0.50, and then increased slightly at higher x values. The saturation magnetization (Ms) decreased monotonically with increasing x, from 67.2 (emu g−1) for pure sample, down to 43.0 emu g−1 for the sample with x = 1.0. The sample with x = 0.25 exhibited magnetic properties suitable for high density magnetic recording, while the samples with higher x values exhibited magnetic softening, prohibiting the potential for such applications.

Microstructure and properties of lanthanide series M-type hexaferrites

A series of M-type hexagonal ferrites with the composition Ba1−xLaxFe11.6Co0.2Ti0.2O19 (x = 0.00, 0.10, 0.15, 0.20, 0.25, 0.30) were prepared by the ceramic process during the whole process of pre-sintering and sintering. The phase composition, micro-morphology, and magnetic properties of the particles were investigated by XRD, SEM, and VSM. With the increase of La content, the single magnetoplumbite phase structure transformed into multiphase structure. Meanwhile, the small amount of α-Fe2O3 phase existed in M-type phase. It was found that powders were crystallized into M-type hexaferrites phase at 1250 °C. The micrographs of the magnetic powders were observed by a field emission scanning electron microscopy (SEM). With different La contents, the micro-morphology of the particles exhibited the uniform plane hexagonal structures of M-type ferrites. The magnetic properties were investigated by Vibrating sample magnetometer (VSM). The saturation magnetization (Ms) increases and then decreases with the increasing of La content. The saturation magnetization (Ms) has the maximum value at x = 0.20 (Ms = 61.85 emu/g). The value of coercivity (Hc) is up to 3428 Oe when the amount of doping is 0.30, and the value of coercivity (Hc) increases with the increasing of La content.

Synthesis, Characterization and Properties of PANI/(La-Nd Doped BaFe&lt;sub&gt;12&lt;/sub&gt;O&lt;sub&gt;19&lt;/sub&gt;) Composites

La-Nd co-doped barium hexaferrites, Ba0.7(LamNdn)0.3Fe12O19 (D-BaM), were successfully prepared by sol-gel method. PANI / D-BaM composites were synthesized by in-situ polymerization in solution. The structure, morphology and properties of samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), four-probe conductivity tester and vector network analyzer. The XRD patterns showed that the crystal structure of all the samples exist as M-type phases. The SEM images revealed that the particles presented a hexagonal platelet-like morphology. The magnetic properties could be improved by substitutions of La and Nd ions. The saturation magnetization (Ms) and coercive force (Hc) increased with the change of La / Nd ratio to the maximum at La / Nd = 3:1. The doped particles have also been embedded in conductive PANI to prepare electromagnetic materials, and the conductivity kept on the order of 10-2. The microwave absorbing properties of composites at 30 MHz-6 GHz improved obviously, the peak value of reflection loss could reach-7.5 dB.

Structural and properties of hydrothermally synthesised M-type hexaferrites

Magnetoplumbite-type (M-type) hexagonal strontium ferrite particles were synthesized by hydrothermal method as the materials. Then, the precursors were calcinated at 1000 °C for two different time (200 and 300 min). The phase composition, micro-morphology and magnetic properties of the particles were investigated by X-ray powder diffraction analysis, scanning electron microscopy, and vibrating sample magnetometer. At hydrothermal temperature ranging from 220 to 230 °C, the phase of M-type hexaferrites includes small amounts of impurities phases, such as α-Fe2O3. The result shows that the single M-type phase was obtained when the hydrothermal temperature is 240 °C. The particles appear in hexagonal plate-like shape and the size of grain is about 400 nm. The effect of sintering time on magnetization and coercivity was studied in this paper.

Effects of La3+-Zn2+ doping on the structure, magnetic, electrical, and dielectric properties of low temperature sintered Sr-hexaferrites

The Sr1-xLaxFe12-xZnxO19 (x=0–0.3) hexaferrites with Bi2O3 additive were prepared by microwave sintering method at low sintering temperatures, and their crystal structure, microstructure, magnetic, electrical, and dielectric properties were studied. The results show that the pure M-type phase is obtained for the ferrites with x≤0.2. With x further increasing to 0.3, the multiphase structure is inevitably formed, where the LaFeO3 phase coexists with the M-type phase. In the single phase region, the varied magnetic, electrical, and dielectric properties with La3+-Zn2+ doping amount are well explained by the occupancy effects of La3+ and Zn2+ in magnetoplumbite structure. It is suggested that the Zn2+ ions replace the Fe3+ ions at 4f1 site with x≤0.15, but the substitution of Zn2+ for Fe3+ occurs at 2b site preferentially when the La3+-Zn2+ doping amount exceeds 0.15.

Synthesis and characterization of Sr1−x Y x Fe12O19 hexaferrites prepared by solid-state reaction method

M-type permanent magnetic ferrite Sr1−xYxFe12O19 (x = 0.00, 0.02, 0.05, 0.08, 0.10, 0.13) magnetic powders have been synthesised by the ceramic process. Phase composition was examined by using X-ray diffraction (XRD). The single magnetoplumite phase structure transformed into multiphase structure with the increase of yttrium content, where the small amount of hematite phase existed in M-type phase. It was found that powders were crystallized into M-type hexaferrites phase at 1250 °C. The micrographs of the magnetic powders were observed by a field emission scanning electron microscopy (SEM). The micro-morphology of the particles exhibits the uniform plane hexagonal structures of M-type ferrites with different yttrium contents. Vibrating sample magnetometer (VSM) was employed to investigate the magnetic properties. With the increasing of yttrium content, the saturation magnetization (Ms) first increases and then decreases. The saturation magnetization (Ms) has the maximum value at x = 0.05 (Ms = 62.74 emu/g). The value of coercivity (Hc) increases with the increasing of yttrium content, and the value of coercivity (Hc) is up to 3634 Oe when the amount of doping is 0.13.

Crystal structure and physical properties of microwave sintered Sr1−xLaxFe12−xCuxO19 (x=0–0.5) ferrites for LTCC applications

The Sr1−xLaxFe12−xCuxO19 (x=0–0.5) ferrites for use in low temperature co-fired ceramics (LTCC) technology were prepared by improved solid phase method. Dependence of their crystal structure, magnetic, electrical, and dielectric properties on La–Cu substitution amount were investigated. Pure M-type phase is obtained for the ferrites with La–Cu substitution amount x≤0.3. With x further increasing to 0.5, the multiphase structure is formed, where the M-type phase coexists with the LaFeO3 phase and Sr2FeO4−x phase. In single M-type phase region with x≤0.3, the varied magnetic properties can be well explained considering the occupancy effects of La3+ and Cu2+ ions in magnetoplumbite structure. Their electrical transport behavior is found to be correlated with La–Cu substitution amount. Single metal–semiconductor (M–S) transition is clearly observed in the ferrites with a high doping amount as x=0.3. The polarization behavior from 1kHz to 10MHz follows the charge polarization mechanism, and the temperature dependence of real permittivity (ε′–T curves) and dielectric loss (tgδ–T curves) strongly suggests the complicated multiparticle polarization and relaxation.

Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with appropriate Bi2O3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC (low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amount x did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such as α-Fe2O3 phase, La2O3 phase, and LaCoO3 phase. Appropriate La-Co substitution improved the Ms (>62 emu/g), Ha (>1400 kA/m), and Hci (>320 kA/m) for the ferrites with x varying from 0.1 to 0.3, but the TC decreased with increasing substitution amount. Moreover, the microwave sintered ferrites could provide larger Hci and similar Ms compared with the conventional sintered ferrites.

Magnetic, electrical, and dielectric properties of La–Cu substituted Sr-hexaferrites for use in microwave LTCC devices

The Sr1-xLaxFe12-xCuxO19 (x = 0–0.4) ferrites with appropriate amount of Bi2O3·B2O3·SiO2·ZnO (BBSZ) glass were prepared by traditional solid phase method at low sintering temperatures compatible with low temperature co-fired ceramics (LTCC) technology. Detailed effects of La–Cu substitution amount on their crystal structure, magnetic, electrical, and dielectric properties were investigated. The results show that the pure M-type phase is obtained for the ferrites with x ≤ 0.3. With further increasing x, the multiphase structure is inevitably formed, where the LaFeO3 phase coexists with the M-type phase. In the single M-type phase region, the variation of magnetic properties with La–Cu substitution amount is well explained based on the occupancy effects of La3+ and Cu2+ in magnetoplumbite structure. Suitable La–Cu substitution with x = 0.25 raises the saturation magnetization to a maximum value of 67.5 emu/g. The intrinsic coercivity decreases from 3.68 to 3.43 kOe with x increasing from 0 to 0.3, which is mainly dominated by the reduced magnetic anisotropy field. Electrical transport behavior of the ferrites is found to follow the impurity semiconductor, and the effect of La–Cu substitution on the direct-current resistivity is observed. Their polarization behavior in test frequency range of 1 kHz–10 MHz obeys the charge polarization mechanism, which happens since the frequency of the hopping of electron exchange between Fe2+ to Fe3+ is far from the frequency of alternating-current field.

Synthesis and characteristics of La3+–Co2+ substituted Sr-hexaferrites for microwave LTCC circulators

The La3+–Co2+ substituted Sr0.7La0.3Fe11.7Co0.3O19 ferrites with 2–5wt% Bi2O3·B2O3·SiO2·ZnO (BBSZ) glass were synthesized by conventional sintering (CS) method, microwave sintering (MS) method, and hot press sintering (HPS) method at a low sintering temperature of 850°C compatible with the low temperature co-fired ceramics (LTCC) systems, respectively. These ferrites were chiefly characterized by X-ray diffraction, precision density balance, and vibrating sample magnetometer. It is observed that the addition of BBSZ can promote the low temperature sintering of the ferrites, as well as the formation of M-type phase. But the excessive addition of non-magnetic BBSZ is inclined to reduce the magnetic properties for the ferrites. Detailed effects of the BBSZ amount on their low temperature sintering characteristics are revealed and explained. The proper addition of BBSZ is suggested to be 4, 4, and 5wt% for the CS ferrites, MS ferrites, and HPS ferrites, respectively. Notably, the obtained MS ferrites can provide relatively high saturation magnetization of 65.3emu/g, magnetic anisotropy field of 1528.8kA/m, and intrinsic coercivity of 336.1kA/m as low temperature sintered M-type hexaferrites for use in microwave LTCC circulators.

Modification of the Magnetic Properties of Co&lt;sub&gt;2&lt;/sub&gt;Y Hexaferrites by Divalent and Trivalent Metal Substitutions

The present study is concerned with the fabrication and characterization of Me2Y substituted hexaferrites, Ba2Me2Fe12-xTxO22(Me = Co2+, Mg2+, and Cr2+, and T = Fe3+, and Ga3+). The samples were prepared by the conventional ball milling technique and sintering at 1200° C. The effect of the choices of Me and T ions on the structural and magnetic properties of the hexaferrites were investigated. XRD patterns, magnetic parameters, and Mössbauer spectra of the Co2Y were consistent with a single phase Y-type hexaferrite. However, the CoCr-Y sample was found to be dominated by the Y-type hexaferrite, and M-type and BaCrO4minority phases were observed in the XRD pattern of the sample. The small increase in saturation magnetization from about 34 emu/g up to 37.5 emu/g was therefore attributed to the development of the M-type phase. On the other hand, XRD pattern of the Cr2Y sample indicated the dominance of the M-type phase in this sample. The high coercivity (1445 Oe) of this sample is evidence of the transformation of the material from a typically soft magnetic material (Y-type) to a hard magnet (M-type). The Ga-substitution for Fe in Co2Y did not affect the saturation magnetization significantly, but the coercivity was reduced. However, the sample Ba2CoMgFe11GaO22exhibited a significant reduction of the saturation magnetization down to a value 26.6 emu/g, which could be due to the attenuation of the super-exchange interactions induced by the Mg2+substitution.

Microwave sintered Sr1−xLaxFe12−xCoxO19 (x = 0–0.5) ferrites for use in low temperature co-fired ceramics technology

The La3+ and Co2+ substituted Sr1−xLaxFe12−xCoxO19 (x = 0–0.5) ferrites with Bi2O3 sintering aid were prepared by microwave sintering method at a low sintering temperature of 870 °C compatible with low temperature co-fired ceramics (LTCC) systems. Detailed effect of La–Co substitution amount on their crystal structure and magnetic properties were mainly investigated. The results show that the pure M-type crystal phase is successfully obtained for the ferrites with La–Co substitution amount x not higher than 0.3. With further increased substitution amount, the multiphase structure is formed, where the non-magnetic α-Fe2O3 phase and LaCoO3 phase coexist with the M-type phase. Appropriate La–Co substitution improves the magnetic properties of the ferrites, including the saturation magnetization Ms, effective magnetic anisotropy constant Keff, magnetic anisotropy field Ha, and intrinsic coercivity Hci. Besides, the Curie temperature TC of the ferrites exhibits a rapid decrease when the La–Co substitution amount exceeds 0.3. It is suggested that the La3+–Co2+ ions can partially substitute the Sr2+–Fe3+ ions for the ferrites, leading to enhanced magnetic properties. Typically, the obtained Sr1−xLaxFe12−xCoxO19 (x = 0.2–0.3) ferrites can provide improved Ms above 64 emu/g, Ha above 1510 kA/m, and Hci above 330 kA/m as low temperature sintered M-type hexaferrites, which are promising for use in future design and realisation of self-biased circulators in LTCC systems.

Effect of La–CO substitution on the crystal structure and magnetic properties of low temperature sintered Sr1−xLaxFe12−xCoxO19 (x=0–0.5) ferrites

The La–Co substituted Sr1−xLaxFe12−xCoxO19 (x=0–0.5) ferrites with appropriate Bi2O3 additive were prepared at a low sintering temperature of 890°C compatible with LTCC (low temperature co-fired ceramics) systems, and the effect of La–Co substitution on their crystal structure and magnetic properties was investigated. The results show that the pure M-type phase is successfully obtained when the La–Co substitution amount x does not exceed 0.3. However, the single M-type phase structure transforms to multiphase structure with further increased x, where the α-Fe2O3 phase and La2O3 phase coexist with the M-type phase. Moreover, the saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC of the ferrites depend on the La–Co substitution amount strongly, which are suggested to be determined by the partially substitution of La3+–Co2+ ions for Sr2+–Fe3+ ions with x not higher than 0.3. It is found that the obtained Sr1−xLaxFe12−xCoxO19 (x=0.2 and 0.3) ferrites can provide improved magnetic properties (Ms>62emu/g, Ha>1400kA/m, and Hci>320kA/m) as low temperature sintered M-type hexaferrites for microwave LTCC applications.