Phase Distribution and Magnetic Properties of Mechanically Alloyed Hard/Soft Ferrite Nanocomposites

Improvement in the magnetic properties of hard/ soft ferrite nanocomposites was studied by varying the composition of the soft phase in SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposites. The SrFe₁₂O₁₉/Ni_0.5Zn_0.5Fe₂O₄ nanocomposites were prepared using the mechanical alloying method. The samples were prepared by varying the amount of the soft phase from 10 to 50 wt% while the amount of the hard phase remained 100 wt% in the ferrite nanocomposites. X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and a transmission electron microscope (TEM) were used to characterize the samples. From the result, it was found that the nanocomposite magnet with 10 wt% of soft phase content had the highest remanence ratio, M _r / M _s , which was 0.61, while the values of the coercivity, H _c , and magnetization, M _s , measured were 4482.4 G and 9.71 emu/g, respectively, and the average particle size of the ferrite nanocomposites was < 50 nm for all the samples. It was also shown that H _c decreased as the weight percent of the soft ferrite increased, which resulted from the dipolar interaction that occurred in the ferrite nanocomposites, showing the effect of phase distribution on the magnetic properties.     

机械合金化纳米晶合金Ni50Bi50的结构和磁性

研究了Ｎｉ５０Ｂｉ５混合粉末在机械合金化过程中结构和磁性的变化。Ｘ射线衍射、差示扫描量热分析和比饱和磁化强度的测量结果表明：混合粉末的晶粒尺寸随球磨时间的增加而减小。球磨２００ｈ时，样品的晶粒尺寸为１５ｎｍ。机械合金化可以提高Ｂｉ在Ｎｉ中的固溶渡。     

Phase Transformation and Magnetic Properties of Mechanically Alloyed PrCo5-based Magnets

PrCo5-based nanograin Pr=CO100-x （x=14-22） alloys with high coercivity were synthesized by mechanical alloying and subsequent annealing. The crystallization, phase components and magnetic properties of the alloys were investigated systematically. The main phase of the alloy for x=14 is Pr2CO17 with rhombohedral Th2Zn17-type. The amount of the Pr2CO17 phase decreases with increasing Pr content, and a nearly single phase PrCo5 with hexagonal CaCu5-type is formed in Pr18Co81 alloy. Further increase in the Pr content leads to the formation of another magnetically hard Pr2Co7 phase with its Curie temperature about 350℃. Remanences decrease monotonously with increasing Pr content, whereas the coercivities increase, reaching a maximum of 2040 kA/m （25.6 kOe） in Pr19CO81 powders milled for 5 h and annealed at 973 K for 2 min, and then decrease for higher Pr content. The high coercivity is attributed to the high anisotropy field of the PrCo~ phase and its nanoscale grain size.     

Magnetic Properties of Zinc Ferrite Nanoparticles Synthesized by Coprecipitation Method

The influence of the precipitant and ferric concentration on the magnetic properties of coprecipitated zinc ferrite nanoparticles has been investigated. The nanoparticles were characterized using X-ray diffraction, scanning and transmission electron microscope, and vibrating sample magnetometer techniques. The results showed that the single-phase zinc ferrite with partially inverse spinel structures can be formed at high concentrations. The inversion coefficient calculated by the Rietveld method decreases with increasing of the concentrations, may be due to the crystal growth. The magnetic measurements exhibited that the coprecipitated zinc ferrite nanoparticles were superparamagnet and magnetization decreases with increasing of the concentrations through decreasing of inversion coefficient.     

Zinc Ferrite Nanoparticles: New Preparation Method and Magnetic Properties

In this work, single phase zinc ferrite (ZnFe₂ O ₄) nanoparticles with a mean crystallite size of 12 nm were successfully prepared just by high energy wet milling of metallic Zn and Fe powders and water as the raw materials, without any subsequent heat treatments. Variation of the magnetization with respect to temperature was studied by Faraday balance. Room temperature M–H curve of the as-milled powder has an s-shape, which shows it has ferrimagnetic order. To investigate the effect of annealing on magnetic properties of the as-milled powder, it was annealed at different temperatures from 150 to 800 °C and characterized by XRD and magnetometry. The results show that cation distribution of the as-milled nanoparticles is different from that of the bulk zinc ferrite (normal spinel) and by annealing it changes drastically, and finally, it changes to that of the bulk one.     

Structural and Magnetic Properties of Cobalt and Copper Ions Mixed Nickel Ferrite Nanoparticles

Co²⁺ and Cu²⁺ ions mixed nickel ferrite nanoparticles were synthesized by sol-gel auto combustion method. XRD patterns revealed the existence of a single-phase cubic spinel structure. The average grain size estimated from XRD patterns was found to be from 42 to 56 nm. VSM study indicates increase in saturation magnetization and decrease in coercivity. FE-SEM images exhibit particles with spherical shape and size ranges from 37 to 79 nm. The two main metal ion vibrations of ferrites were observed in FT-IR spectra.     

掺Dy3+铁氧体纳米磁颗粒尺寸与磁学特性的相关性

在水相体系中用化学法制备出不同尺寸的掺Dy3+铁氧体纳米磁颗粒。采用透射电子显微镜(TEM)、X射线衍射仪(XRD)、超导量子干涉仪(SQUID)表征了样品的形貌、结构、室温磁学性能。TEM图片表明,样品的形貌近似球形,平均粒径在15～24nm之间;XRD图谱表明,磁颗粒的物相以Fe3O4为主,结构为面心立方尖晶石型;SQUID测试结果表明,磁颗粒的尺寸不同则磁学特性有所不同,呈现出饱和磁化强度(Ms)随粒径增大而升高的规律;粒径小则剩余磁化强度(Mr)、矫顽力(Hc)小,粒径增大则剩余磁化强度、矫顽力升高。     

Effect of Barium on Morphological Transition and Magnetic and Dielectric Properties in Ferrite Nanoparticles

Barium ferrite (BaFe₂O₄) nanoparticles were synthesized by auto combustion method under different weight percentages of barium. The role of barium in the behavior of spinel ferrite property is identified from this study. XRD exhibits prominent orientation of (212) for BaFe₂O₄ has confirmed especially in 20 and 30 wt% of barium. The addition of barium metal induced the specific vibration in FTIR spectra and such changes coincide well with the particle size. Further, the EDX spectrum reflects the atomic percentage of elemental presence in the samples of barium ferrite. Addition of barium on ferrite nanoparticles reduces the intensity of fluorescence. The morphological changes occurred due to increasing doping concentration of barium and is visualized from the FESEM and TEM images. The formation of different morphologies such as spherical, hexagonal platelets and small rectangular bar shape are observed only due to inclusion of barium at surfactant medium. The magnetic properties of the barium ferrite samples are studied by VSM. It reveals that 35.11 emu/g saturation magnetization (M _s ) with 3775.08 Oe coercivity. The change in values of coercivity (H _c ) from 3775.08 to 1572.95 Oe due to the variation of barium levels confirmed that the role of barium induced the hard magnetic behavior. The dielectric study also indicates the significance of barium ferrite in the variation of dielectric constant.     

Physical Characterization,Optical Properties,and Magnetic Interactions of Cadmium-Doped Zinc Ferrite Nanoparticles

Journal of Superconductivity and Novel Magnetism - The physical characterization and magnetic interactions of cadmium-doped zinc ferrite nanoparticles...     

Ni_(1-x)Co_xFe_2O_4铁氧体纳米粉末的磁性能和微波吸收特性

利用柠檬酸溶胶-凝胶自蔓延燃烧法合成了Ni1-xCoxFe2O4(x=0,0.1,0.3,0.5)铁氧体纳米粉末。利用XRD、VSM和矢量网络分析仪测定了粉末样品的晶体结构、磁性能和电磁参数。定性分析了样品的饱和磁化强度、矫顽力、复磁导率和复介电常数随频率和Co含量的变化关系。结果表明,自蔓延的所有粉末样品经过600℃,2h高温退火后均为尖晶石相纳米晶颗粒。随着Co替代量x的增加,样品的自然共振频率先增大后减小,并对微波吸收特性有一定的改善。     

锂铁氧体纳米晶的磁性能研究

我们用ＰＥＧ凝胶法合成出的ＬｉＦｅ＿５Ｏ＿３纳米晶，用ＸＲＤ和ＴＥＭ观测其粒径和形貌。用振动样品磁强计考察其比饱和磁化强度σ＿ｓ，随粒径口变化，得到样品的σ＿ｓ随Ｄ的减小而下降。     

尖晶石型铁氧体纤维的制备及磁性能

以柠檬酸和金属盐为原料, 采用有机凝胶-热分解法制备了MeFe₂O₄(Me=Zn, Ni_0.5Zn_0.5, Ni_0.4Zn_0.4Cu_0.2)铁氧体纤维.通过FT-IR、XRD、TG-DSC、SEM和VSM等测试技术对纤维前驱体凝胶的结构、热分解过程及热处理产物的物相、形貌以及纤维的磁性能等进行了表征.结果表明, 在凝胶形成过程中, 金属离子单齿或双齿螯合配位于柠檬酸根阴离子, 形成线型分子结构, 使凝胶有较好的可纺性. 所制得的纤维具有较大的长径比, 纤维直径在0.5～20.0μm之间.这些纤维在室温下都具有软磁特性, 化学组成、晶粒大小及形貌对纤维的磁性能有着显著影响.ZnFe₂O₄、Ni_0.5Zn_0.5Fe₂O₄和Ni_0.4Zn_0.4Cu_0.2Fe₂O₄纤维的饱和磁化强度分别为2.6、12.7和40.0A·m²·kg^-1, 相应的矫顽力分别为4.77、5.82和4.04kA·m^-1.     

Synthesis and Properties of Magnetic Nanoparticles

The uniform mesoporous SBA-15 consisting of SiO2 with long-range channels Offers an excellent host material to synthesize or assemble the magnetic nanocomposites, such as Fe, Ni. In this paper, highly dispersed and uniform iron nanoparticles were incorporated into the pore channels of SBA-15 through a newly developed strategy in which some kinds of coupling agents were used to entrap the nanoparticles into the silica framework. The X-ray diffraction （XRD）, fourier transmission infrared spectroscopy （FTIR）, high-resolution transmission electronic microscopy （HRTEM） and energy dispersive X-ray spectroscopy （EDX） were performed to further identify the successful incorporation and grafting of iron. Compared with other ordinary non-assembled magnetic nanoparticles, the assembled Fe nanoparticles with the diameter even in the size range of 5～6 nm still have better magnetic properties.     

Investigation of Phase Formation and Magnetic Properties of Mn Ferrite Nanoparticles Prepared via Low-Power Ultrasonic Assisted Co-precipitation Method

MnFe₂O₄ nanoparticles were synthesized by low-power ultrasonic assisted co-precipitation at two different aging times. In order to investigate the effect of ultrasonic waves on phase formation and magnetic properties of Mn ferrite nanoparticles, two other samples were synthesized in the same conditions but in the absence of ultrasonic waves. Structural and morphological properties of the nanoparticles were examined by using X-ray diffraction (XRD) and scanning electron microscope (SEM). The presence of ultrasonic waves through the reaction medium led to form a single phase of MnFe₂O₄ at 15 min aging time, while this time was insufficient to form a single phase in the absence of ultrasonic waves. At 60 min aging time, the crystallinity of the sample synthesized in the presence of ultrasonic waves was greater and its particle size was bigger than those of the sample synthesized in the absence of ultrasonic waves. The observed results were evaluated from physico-chemical point of view. It was concluded that the ultrasonic waves led to a slower nucleation rate. The magnetic properties of the nanoparticles were examined by permeameter and Faraday-balance equipment. The saturation magnetization of the sample prepared in the presence of ultrasonic waves was enhanced and its Curie temperature was reduced.     

Studies on the Properties of Manganese Substituted Nickel Ferrite Nanoparticles

Mn²⁺-substituted Ni ferrite nanoparticles were synthesized by sol-gel auto combustion method. The synthesized samples were annealed at 800 ^°C and characterization studies were carried out by XRD, VSM, electron paramagnetic resonance (EPR), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. The XRD patterns revealed that Mn ²⁺-substituted Ni ferrite crystallizes in cubic spinel phase and addition of α-Fe ₂ O ₃ phase was also observed. The average crystallite sizes were found to be from 42 to 56 nm using a Scherer equation. The coercivity and remanent magnetization decreases when Mn ²⁺ ion concentration is increased. The EPR spectrum shows the phase homogeneity of the samples. The FE-SEM images revealed that particles are both spherical in shape and particle sizes varied from 22 to 41 nm. The FT-IR spectrum confirmed the two main metal ion vibrations of nickel ferrite near 550 to 560 cm ^?1 (A site) and 441 to 460 cm ^?1 (B site).     

微波锂系铁氧体的磁性能研究

本文用正交试验设计方法研究了微波锂系铁氧体的微观结构参数(气孔率和平均晶粒尺寸)和微波磁性能(饱和磁化强度、共振线宽和介电损耗)随成分、工艺的变化规律,获得了可应用在低功率器件中的6366A/m(80_(?))的铁磁共振线宽铁氧体。首先,根据极差对不同成分、工艺对各参数和性能的影响进行了分析,表明Mg和Ti(1∶1)的取代量对多晶锂铁氧体材料的气孔率、饱和磁化强度和共振线宽的影响最显著,而Ca和V(2∶1)的取代量和烧结温度则分别对平均晶粒尺寸和介电损耗的影响最显著。同时,也对各因素的影响机理作了相应的探讨。最后,本文对多晶锂系铁氧体的成分-组织-性能间的联系进行了线性回归分析,结果表明气孔率和平均晶粒尺寸在很大程度上决定着多晶系铁氧体的共振线宽,并且前者的作用比后者的作用要大。     

参杂尖晶石型镍基铁氧体的磁性能与介电性能

采用溶胶-凝胶法制备了立方晶系尖晶石型镍基铁氧体微粉Ni0.5M0.5Fe2O4（M=Zn、Mn、Cu）,采用X射线衍射仪、扫描电子显微镜、振动样品磁强计和矢量网络分析仪对粉末的结构、形貌、磁性以及电磁性能进行了表征,结果表明,三种粉末在室温下具有超顺磁性,其饱和磁化强度MS分别为76．0、59．4和54．4emu·g-1。在2—11GHz范围内,Ni0.5M0.5Fe2O4的电磁损耗角正切值tgδ随频率的增大而逐渐减小;Ni0.5M0.5Fe2O4和 Ni0.5M0.5Fe2O4的tgδ随频率的增大先增大后减小。