The magnetic and dielectric properties of multiferroic Sr-substituted Zn_2-Y hexagonal ferrites

The magnetic and dielectric properties of Sr-substituted Zn2-Y hexagonal ferrites （Ba2-x SrxZn2Fe12O22, 1.0 〈 x ≤ 1.5） are studied in this paper. Sr substitution will lead to the variation of cation occupation, which influences both the magnetic and electric properties. As Sr content x rises from 1.0 to 1.5, magnetic hysteresis loop gets wider gradually and the permeability drops rapidly due to the transformation from ferrimagnetic to antiferromagnetic phase. Moreover, permittivity rises with increasing Sr content. Under a certain external magnetic field, the phase transition of helical spin structure of Ba0.5Srl.5Zn2Fe12O22 at about 295 K seems to open a possibility for the room-temperature ferroelectricity induced by magnetic field. But its low resistivity prevents the observation of ferroelectric and magnetoelectric properties at room-temperature.

Single-negative properties of Ba_2Co_(1.8)Cu_(0.2)Fe_(12)O_(22) and Ba_3Co_2Fe_(23.4)Zn_(0.6)O_(41) hexagonal ferrites

The electromagnetic properties of Ba2Co1.8Cu0.2Fe12O22 （Co2Y） and Ba3Co2Fe23.4Zn0.6O41 （Co2Z） were studied by measuring microwave scattering parameters.In the transmission spectra of Ba2Co1.8Cu0.2Fe12O22,a forbidden band emerges due to ferromagnetic resonance,and the permeability will turn to negative in the vicinity of the ferromagnetic resonance frequency.In the complex permittivity spectra of Ba3Co2Fe23.4Zn0.6O41,the negative permittivity can be obtained due to dielectric resonance.Therefore,Co2Y and Co2Z can be used to construct left-handed materials possessing negative permeability and negative permittivity simultaneously.

Synthesis of hexagonal barium ferrite nanoparticle by sol-gel method

M-type Ba hexaferrites were successfully synthesized by sol-gel method. Several synthesizing factors, such as pH value, citric acid/metal ion ratio, and dispersion agent were mainly discussed. Fine and pure powders of BaFe12O19 were optimally synthesized under the conditions of the pH value is 7 and citric acid/metal ion ratio is 3. The X-ray diffraction analysis demonstrates that no impurity is observed in the synthesized powders after presintered at 450 ℃ and calcinated at 1100 ℃. SEM observations indicate that the size of the synthesized BaFe12O19 powders is small and uniform distribution. It can also be learned from SEM that the co-synthesizing sol-gel method can be in favor of the formation of finer particles.

Synthesis and Microwave Electromagnetic Properties of M-type Hexagonal FerriteBaTiCoFe_(10)O_(19)

An M-type hexagonal ferrite BaTiCoFe10 O19 was prepared by solid phase reaction by a partial 2Fe3+→Ti4+ Co2+ substitution. The morphology observation and phase identification of BaTiCoFe10O19 were carried out by SEM and XRD, and its X-ray powder diffraction data was reported in this paper for the first time. Further, the microwave electromagnetic properties of BaTiCoFe10O19 were measured and discussed.

Microstructure,magnetic properties of hexagonal barium ferrite powder based on calcination temperature and holding time

In this paper,single-phase and fine-grain hexagonal barium ferrite powder was prepared based on the optimal calcination condition.The influence of calcination conditions including temperature and holding time on microstructure and magnetic properties of powder were studied in detail.Firstly,θ-2θ scan X-ray diffraction(XRD) results reveal that it is hard to obtain single phase of powder when the calcination temperature is lower than 850℃.In addition,the calcination time for single phase of barium ferrite powder was reduced with the increase in calcination temperature.Scanning electron microscopy(SEM) images and magnetic hysteresis loops show that the condition of low temperature and long holding time is beneficial for obtaining homogeneous size of grain and excellent magnetic properties.Consequently,hexagonal barium ferrite powder with uniform grain size of~180 nm,high purity and excellent magnetic properties is obtained at optimal calcination condition of 850℃-10.0 h.

Low-fired Y-type hexagonal ferrite for hyper frequency applications

Y-type hexagonal ferrite with planar magnetocrystalline anisotropy has ultrahigh cut-off frequency up to GHz and excellent magnetic properties in hyper frequency range,so that is regarded as the most suitable material in correpongding inductive devices and components.The technology of low temperature cofired ceramics for surface-mounted multilayer chip components needs ferrite to be sintered well under 900℃to avoid the melting and diffusion of Ag inner electrode during the cofiring process.To lower the sintering temperature of Y-type hexagonal ferrite,there are several methods,(1)using nano-sized starting powders,(2)substitution by low-melting elements,(3)adding sintering additives,and(4)introducing lattice defect.In this paper,the effects of different methods on the sintering behavior and the magnetic properties were discussed in detail.