Papers by Keyword: Hard Ferrites

Abstract: Hexagonal ferrites, or hexaferrites, are hugely important materials commercially and technologically, with common applications as permanent magnets, magnetic recording and data storage media, components in electrical devices operating at wireless frequencies, and as GHz electromagnetic wave absorbers for EMC, RAM and stealth technologies. Hexaferrites are all ferrimagnetic materials, and their magnetic properties are intrinsically linked to their crystalline structures, all having a strong magnetocrystalline anisotropy; that is the induced magnetisation has a preferred orientation within the crystal structure. They can be divided into two main groups: those with an easy axis of magnetisation (known as uniaxial), the hard hexaferrites, and those with an easy plane (or cone) of magnetisation (known as ferroxplana or hexaplana), soft ferrites. The common hexaferrite members are:M-type ferrites, such as BaFe₁₂O₁₉ and SrFe₁₂O₁₉Z-type ferrites (Ba₃Me₂Fe₂₄O₄₁)Y-type ferrites (Ba₂Me₂Fe₁₂O₂₂)W-type ferrites (BaMe₂Fe₁₆O₂₇)X-type ferrites (Ba₂Me₂Fe₂₈O₄₆)U-type ferrites (Ba₄Me₂Fe₃₆O₆₀)where Me = a small 2⁺ ion such as cobalt, nickel or zinc, and Ba can be fully substituted by Sr. Generally, the M ferrites are hard, the Y, Z and U ferrites are soft, and the W and X ferrites can very between these two extremes, but all have large magnetisation (M) values.There is currently increasing interest in composite materials containing hexaferrite fibres. It had been predicted that properties such as thermal and electrical conductivity, and magnetic, electrical and optical behaviour will be enhanced in material in fibrous form. This is because a continuous fine fibre can be considered as effectively one-dimensional, and it does not behave as a homogeneously distributed solid. Although the intrinsic magnetisation of the material is unaffected, the effective magnetisation of an aligned fibre sample should be greater when a field is applied parallel with fibre alignment compared to when applied perpendicularly to fibre alignment. This feature was first demonstrated by the author for aligned hexaferrite fibres in 2006. This chapter will deal with progress in the manufacture and properties of hexaferrite fibres, from the first syntheses of BaM, SrM, Co₂Y, Co₂Z, Co₂W, Co₂X and Co₂U micron-scale fibres by the author 12-15 years ago, to recent developments in M ferrite hollow fibres and nanofibres, and hexaferrite-coated CNTs (carbon nanotubes).The relative properties of all reported hexaferrite fibres are compared and summarised at the end of this chapter.

Abstract: Swift heavy ion irradiation of material is a unique tool to modify the properties of the material and it provides an alternative to photons for introducing electronic excitations into the material. In the present investigation, the changes in structural, morphological and magnetic properties of SrFe₁₂O₁₉ ferrite (prepared using co-precipitation and SHS routes), induced by 200 MeV Ag⁺¹⁶ ion irradiation have been studied. In order to study the effect of the electronic stopping power (dE/dX) e on these properties the energy of the projectile was so chosen that it could easily pass through the samples. Structural properties of these ferrites have been studied and compared with the properties after Swift Heavy Ion (SHI) irradiation of 200 MeV Ag¹⁶⁺ at different fluences. Samples were characterized using different experimental techniques, like Fourier Transform Infra-red (FT-IR), X-ray Diffraction (XRD), Scanning Electrom Microscope (SEM), Vibrating Sample Magnetometer (VSM) and LCR meter. FTIR spectra for pristine as well as the irradiated samples were recorded for wave number ranges from 4000-400 cm^-1 using the KBr pellet method. FTIR measurement of the bonds' vibration modes in all samples were carried out to determine the change in MO bonding due to irradiation. The MO absorption band is observed in all samples. The intensity of absorption bands increased in irradiated samples, which confirms the formation of strong ferric oxide band. Crystallinity of pristine and irradiated samples was investigated by XRD technique. All XRD peaks were indexed using POWDER X software. XRD result confirms the formation of mono phase. It is observed from XRD analysis that after the irradiation, the intensity of all the peaks and FWHM were increased. There is no significant change in peak position but the intensity is decreased and FWHM is increased continuously with ion fluence. XRD patterns confirm that the ferrite structure is retained even after irradiation. Surface morphology of pristine and irradiated samples was studied using a scanning electron microscopy. It is observed from SEM images that the particle size decreases after irradiation and particles become more homogeneous. Dielectric and magnetic measurements were also carried out.