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1.
Due to the anisotropy of the hyperfine interactions and dipolar fields in hexagonal BaFe12O19, the nuclear magnetic resonance frequency of 57Fe-nuclei at different positions in domain walls situated well within the bulk samples can be detected. The dependence of the enhancement factor η on the position in the wall was measured at 4.2 K and found in good agreement with the dependence expected for a 180°-Bloch-wall. For nuclei in the wall center, a nearly uniform enhancement factor of η = 6.3 × 103 is found. There is no evidence for a broad distribution of η due to wall pinning effects. 相似文献
2.
Jiangying Yu Shaolong Tang Lin Zhai Yangguang Shi Youwei Du 《Physica B: Condensed Matter》2009,404(21):4253-4256
Rod-like and platelet-like nanoparticles of simple-crystalline barium hexaferrite (BaFe12O19) have been synthesized by the molten salt method. Both particle size and morphology change with the reaction temperature and time. The easy magnetization direction (0 0 l) of the BaFe12O19 nanoparticles has been observed directly by performing X-ray diffraction on powders aligned at 0.5 T magnetic field. The magnetic properties of the BaFe12O19 magnet were investigated with various sintering temperatures. The maximum values of saturation magnetization (σs=65.8 emu/g), remanent magnetization (σr=56 emu/g) and coercivity field (Hic=5251 Oe) of the aligned samples occurred at the sintering temperatures of 1100 °C. These results indicate that BaFe12O19 nanoparticles synthesized by the molten salt method should enable detailed investigation of the size-dependent evolution of magnetism, microwave absorption, and realization of a nanodevice of magnetic media. 相似文献
3.
We show a possibility to determine the parameters characterizing surface magnetic anisotropy of platelet BaFe12O19 nanocrystals with thickness comparable to the magnetoperturbed surface layer of high-anisotropic hexagonal crystal. Taking into account the above-mentioned specific character of the particles, we introduce the constant KS as the surface anisotropy energy per unit volume of near-surface layer. Temperature dependence of the surface anisotropy field as one of the components of effective anisotropy was corrected taking into account the thermal fluctuations. Discovered anomaly initiated calculation of the surface anisotropy constant with different approaches for two different temperature ranges. Analyzing the KS sign changes with temperature, we conclude about the transformation of surface anisotropy from plane to axis type. 相似文献
4.
The dielectric properties of a 2.5 mol% Bi2O3 doped Ba-ferrite (BaFe12O19) have been investigated. The specimen shows a drastically enhanced (≈ 105 times) permittivity (ε) through local polarization of Fe3+ electronic charges activated with nearby Bi3+ sites. The ε value also depends reasonably on thermal annealing (causes grain growth) of the samples. The specimens comprising large particle sizes (1–20 μ m) usually exhibit smaller ε values and low dielectric losses. 相似文献
5.
6.
It was observed that the nanocrystallites of BaFe12O19 formed at 140°C under a 0.25 T magnetic field exhibited a higher saturation magnetization (6.1 emu/g at room temperature) than that of the sample (1.1 emu/g) obtained under zero magnetic field. Both of the two approaches yielded plain-like particles with an average particle size of 12 nm. However, the Curie temperature (Tc), a direct measuring of the strength of superexchange interaction of Fe3+–O2−–Fe3+, increased from 410°C for the nanoparticles prepared without an external field applied to 452°C for the particles formed under a 0.25 T magnetic field, which indicates that external magnetic fields can improve the occupancy of magnetic ions and then increase the superexchange interaction. This was confirmed by electron paramagnetic resonance and Mössbauer spectrum analysis. The results present in this paper suggest that in addition to oxygen defects, surface non-magnetic layer and a fraction of finer particles in the superparamagnetic range, cation vacancies should be responsible for the decreasing of saturation magnetization in magnetic nanoparticles. 相似文献
7.
Ugur Topal 《中国物理快报》2010,27(11):177-180
We investigate the effects of B2O3 addition on structural and magnetic properties of hard magnetic BaFe12O19 particles. The conventional solid state reaction method is used as the synthesis route. Single phase BaFe12O19 could be synthesized with very small amounts of B2O3 addition and with calcination at low temperatures (850°C) in short times (1 h). B2O3 addition also improves the magnetic parameters significantly. Remanence magnetization and specific magnetization at 1.5 T increase by ~40% in magnitude although no significant variations on coercivity is observed. 相似文献
8.
Single phase BaM (BaFe12O19) ferrites are prepared by using sol–gel method. The preparing conditions of samples are investigated in detail, such as acid/nitrate ratio, the value of pH and annealing temperature. The best conditions on preparing BaFe12O19, which can be obtained on a Fe/Ba ratio of 12, the citric acid contents R = 3, the starting pH of solution is 9, and annealing temperature 950 °C. The thermal decomposition behavior of the dried gel was examined by TG–DSC, the structure and properties of powders were measured respectively by XRD techniques. The magnetic properties of barium ferrites are emphatically researched about the changing crystallite size and annealing temperature by the vibrating sample magnetometer (VSM). Magnetic measurement shows that the barium ferrite samples annealed at 1000 °C has the maximal coercive field of 5691.91 Oe corresponding to the maximal remnant magnetization of 35.60 emu/g and the sample synthesized at 1000 °C has the maximal saturation magnetization of 60.75 emu/g. 相似文献
9.
Polyaniline/BaFe12O19 (PANI/Ba ferrite) composites were synthesized by in situ polymerization at different aniline/Ba ferrite weight ratios (Ani/Ba ferrite=1/2, 1/1 and 2/1) and introduced into epoxy resin to be microwave absorber. The spectroscopic characterizations of the formation processes of PANI/Ba ferrite composites were studied using Fourier transform infrared, ultraviolet-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave-absorbing properties were investigated by measuring complex permittivity, complex permeability and reflection loss in the 2-18 and 18-40 GHz microwave frequency range using the free space method. The results showed that a wider absorption frequency range could be obtained by adding different polyaniline contents in Ba ferrite. 相似文献
10.
S. Pignard H. Vincent E. Flavin F. Boust 《Journal of magnetism and magnetic materials》2003,260(3):437-446
Polycrystalline samples of M-type hexaferrites BaFe12−2xRuxZnxO19 and BaFe12−2xRuxCoxO19 with 0x0.45 have been prepared by a classical sintering method. The evolutions with x of the cell parameters, the saturation magnetization and the magnetic transition temperature have been measured; in this range of small doping ratios, saturation magnetization and Curie temperature of substituted hexaferrites remain close to those of the undoped BaFe12O19. X-ray diffraction measurements on oriented powders show that a change of magnetocrystalline anisotropy from axial to planar occurs in both cases for a small substituting ratio xc=0.375. Microwave electromagnetic characteristics have been studied on the ceramic samples from 0.1 to 10 GHz. The behaviour of the magnetic losses (μ″) corroborates the anisotropy change when doping; a convolution of the dissipation mechanisms (domain wall motions and gyromagnetism) is obtained for xc. The level of the magnetic losses is discussed in relation with others substituted Ba-hexaferrites. 相似文献
11.
本文对Mn离子取代M型钡铁氧体BaFe12-xMnxO19作了较系统的研究。主要结论如下:(1)在我们的实验条件下,Mn的取代量x可达4,其中约有0.1—0.3的Mn2+存在,其余Mn为三价。(2)Mn离子主要进入12k和2a晶位。(3)BaFe12-xMnxO19的各向异性常数K19,居里温度Tc和饱和磁化强度σs均随x的增加而下降。(4)Mn引起BaFe12-xMnxO19的非共线自旋结构。(5)Mn3+在12k和2a晶位中的平均零场劈裂因子Dh比尖晶石中八面体B位上的Mn3+之Dc值小近一个数量级。
关键词: 相似文献
12.
Hüseyin Sözeri 《Journal of magnetism and magnetic materials》2009,321(18):2717-2722
We report a new synthesis route for preparation of single-domain barium hexaferrite (BaFe12O19) particles with high saturation magnetization. Nitric acid, known as a good oxidizer, is used as a mixing medium during the synthesis. It is shown that formation of BaFe12O19 phase starts at 800 °C, which is considerably lower than the typical ceramic process and develops with increasing temperature. Both magnetization measurements and scanning electron microscope micrographs reveal that the particles are single domain up to 1000 °C at which the highest coercive field of 3.6 kOe was obtained. The best saturation magnetization of ≈60 emu/g at 1.5 T was achieved by sintering for 2 h at 1200 °C. Annealing at temperatures higher than 1000 °C increased the saturation magnetization, on the other hand, decreased the coercive field which was due to the formation of multi-domain particles with larger grain sizes. It is shown that the best sintering to obtain fine particles of BaFe12O19 occurs at temperatures 900-1000 °C. Finally, magnetic interactions between the hard BaFe12O19 phase and impurity phases were investigated using the Stoner-Wohlfarth model. 相似文献
13.
The composite films with different weight ratio of barium ferrite to titanium dioxide are successfully prepared using sol-gel method for the first time. The morphology, crystal structure and magnetic properties of composite films are investigated with atomic force microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that the composite films are uniform with no microcracks. The grain diameters are less than 100 nm. With the increase of barium ferrite, the grain diameter decreases. The composite films are composed of M-type hexagonal barium ferrite and rutile titanium dioxide. The composite films possess the excellent magnetic properties. The specific saturation magnetization and coercivity reach 18.3 emu/g and 3350 Oe, respectively. The application of composite films in magnetic recording and electromagnetic absorption fields is promising. 相似文献
14.
Ugur Topal 《Physica B: Condensed Matter》2012,407(12):2058-2062
In the present study, the effects of B2O3 addition on the remanence properties of barium ferrite magnets are examined. The relationship between isothermal magnetization remanence MR(H) and demagnetization remanence MD(H) for non-interacting single domain particles, MD(H)=MR(Hmax)−2MR(H), was used in order to investigate the interactions between particles. We have found that remanence magnetization MR increased by 40% in magnitude with B2O3 addition in addition to the weakened couplings between particles. The B2O3 addition seems to supply the required conditions for usage of these materials in the magnetic recording media. 相似文献
15.
Nanocomposite of hard (BaFe12O19)/soft ferrite (Ni0.8Zn0.2Fe2O4) have been prepared by the sol–gel process. The nanocomposite ferrite are formed when the calcining temperature is above 800 °C. It is found that the magnetic properties strongly depend on the presintering treatment and calcining temperature. The “bee waist” type hysteresis loops for samples disappear when the presintering temperature is 400 °C and the calcination temperature reaches 1100 °C owing to the exchange-coupling interaction. The remanence of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite with the mass ratio of 5:1 is higher than a single phase ferrite. The specific saturation magnetization, remanence magnetization and coercivity are 63 emu/g, 36 emu/g and 2750 G, respectively. The exchange-coupling interaction in the BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite is discussed. 相似文献
16.
The single domain size of BaFe12O19 powder with crystallite sizes less than 200 nm was produced using a citric acid precursor method. Fe3+ and Ba2+, in a molar ratio of 12, were chelated by COOH− in an aqueous solution. After ethylene glycol additions, esterification, dehydration, and calcination led to the formation of ester-derived BaFe12O19 powder. High pH and/or high citric acid contents in the starting solution are required to complete chelate metallic ions in the solution and to form pure barium ferrite powder at 1073 K. Pure single magnetic domain BaFe12O19 particles of M(30 kOe)≈54 emu/g, Mr≈28 emu/g, and Hc≈3.7 kOe were produced using [citric acid]/[metallic ions]=1.5 and pH7. 相似文献
17.
Guoqing Xu Hongliang MaMinjian Zhong Jiong ZhouYuezhong Yue Zhengming He 《Journal of magnetism and magnetic materials》2006
BaFe12O19 powders with nanocrystalline sizes were produced by sol–gel auto-combustion. Fe3+ and Ba2+, in a molar ratio of 11.5, were chelated by citric acid ions at different pH. After dehydration, auto-combustion and calcinations, BaFe12O19 powders were formed. TG/DSC indicated the action to form BaFe12O19 first occurred at about 800. XRD patterns of the annealed powders showed that the well-crystalline powder was produced when pH=10. In addition, the data from XRD showed the lattice parameters a and c, and the unit-cell volume V had a little decrease and the density went up with the increasing pH. The data from PPMS exhibited that pH in the starting solution had an important influence on magnetic properties. In this case, BaFe12O19 powder, of maximum magnetization M(3 T)≈60 A m2/kg, the remanent magnetization Mr≈33 A m2/kg and the intrinsic coercive Hc≈432 kA/m, was produced under the molar ratio of citric acid to the metal nitrate of 1.5 when pH=10. 相似文献
18.
C.C. YangY.J. Gung C.C. ShihW.C. Hung K.H. Wu 《Journal of magnetism and magnetic materials》2011,323(7):933-938
The (BaFe12O19+BaTiO3)/polyaniline composite was synthesized by in situ polymerization and introduced into epoxy resin and polyethylene to be a microwave and infrared absorber. The spectroscopic characterizations of the formation processes of (BaFe12O19+BaTiO3)/polyaniline composite were examined using Fourier transform infrared, ultraviolet-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing properties were investigated by measuring reflection loss in 2-18 and 18-40 GHz microwave frequency range using the free space method. Thermal extinction measurements in the 3-5 and 8-12 μm were done to evaluate the shielding effectivity of infrared. The results showed that a significant absorption frequency range shifting and thermal extinction could be obtained by adding polyaniline to the BaFe12O19+BaTiO3 blend. 相似文献
19.
Jeevan JalliYang-Ki Hong Gavin S. AboSeok Bae Jae-Jin LeeJi-Hoon Park Byoung C. ChoiSeong-Gon Kim 《Journal of magnetism and magnetic materials》2011,323(21):2627-2631
Magnetic domain patterns in bulk barium ferrite (BaFe12O19; BaM) single crystals on the basal plane and the prism plane were measured and studied by magnetic force microscopy (MFM). The surface domain pattern is in the form of flowers or star on the basal plane and long elongated spikes or stripe domains on the prism plane. The change in domain structure with applied field (Happ) and the thickness (T) dependence on domain width (δ) was observed. The domain width decreased from 32 to 9 μm for the crystals of 800-100 μm thicknesses, respectively. 相似文献
20.
Microwave-assisted synthesis of SrFe12O19 hexaferrites 总被引:1,自引:0,他引:1
Wang Zhanyong Zhong Liuming Qian Huichun Fang Yongzheng Xu Jiayue 《Journal of magnetism and magnetic materials》2010,322(18):2782-2785
Ultra-fine and homogeneous SrFe12O19 hexaferrites were synthesized by a microwave-assisted calcination route. The calcined precursors were prepared by a sol-gel auto-combustion method using Fe(NO3)3·9H2O, Sr(NO3)2 and citric acid as starting materials. The structures, powder morphology and magnetic properties of the products were characterized by X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. The results showed that microwaves are helpful to reduce the calcination temperature and shorten the calcination time. The ferrites with saturation magnetization, remanence and intrinsic coercivity of 54.80 emu/g, 29.52 emu/g and 5261 Oe, respectively, were obtained in samples calcined at 800 °C for 80 min. 相似文献