Doped Strontium Hexaferrite Research Articles

Investigation of Structural, Magnetic and Dielectric Properties of Terbium Doped Strontium Hexaferrite for High Frequency Applications

Background/Objectives: Microwave absorbing materials can be used to reduce electro- magnetic interference. M-type hexaferrites (SrFe12O19 and BaFe12O19) have attracted intensive attention on account of their important applications in microwave absorbing materials. Methods/Statistical Analysis: M-type hexaferrite nanoparticles with a composition of TbxSr1-xFe12O19 (x = 0-0.1) were amalgamted by a chemical method known as co-precipitation method. A successive solid state reaction at different calcination temperatures at fixed holding time has lead to the formation of pure and Tb substituted strontium hexaferrite. The reaction of swaping of Tb cations on the magnetic, structural, and electrical properties of nanoparticles was characterized by X-ray diffraction XRD, FTIR,TEM and VSM. Findings: Microstructure by TEM showed that grains are of extremely fine phase. Identification by XRD confers the single-phase material of nanometeric size. Evaluation on magnetic characteristics for the material showed that coercivity decreased progressively as number of Tb3+ ion increases. Although this was followed by a significant increase in total magnetization. Reflection loss and reflection coefficient and loss tangent for a range of 1-5 KHz were derived which confirms that the material can be considered for high frequency applications.

Dielectric properties, cationic distribution calculation and hyperfine interactions of La3+ and Bi3+ doped strontium hexaferrites

La3+ and Bi3+ doped M-type strontium hexaferrites (SrM) were prepared by sol–gel-auto combustion. X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating Simple Magnetometer (VSM), Mössbauer Spectroscopy and Novo electrical conductivity system were used for structural, morphological, and electrical characterizations of the products. The cation distribution calculations of the products were also provided. Single-phase M-type SrM with a chemical composition SrFe12−2xLaxBixO19 (0.0≤x≤0.5) were confirmed by XRD analysis, which also provided lattice constants and crystallite sizes of each product. The crystallite size was in the range of 43–51nm. SEM analysis confirmed the presence of hexagonal crystal formation while the EDX analysis confirmed the presence of metal ions in the required stoichiometric ratio. From 57Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Bi and La substitutions have been determined. It was observed that ac conductivity of SrM increases slightly with increasing La3+ and Bi3+ ion substitutions at first, and then fluctuates with further substitution. Moreover, ac conductivity also increased with increasing frequency which could be regarded as an indication of ionic conductivity. It can be noted that activation energy increases as the enhanced contributions of doped-ion substitutions in SrM NPs with the illustration of a better stability of electrical bonds among the substitutional ions and Fe ions.

Study of dielectric relaxations in co-precipitated Sr–Fe(Cr) nanoferrites

Chromium (Cr) doped strontium hexaferrites with nominal composition SrFe12−xCrxO19 (x = 0.0, 0.1, 0.2, 0.3) were prepared using co-precipitation method. Thermal analysis of the samples was carried out using thermogravimetric analysis and differential scanning calorimetry to study the thermal stability as well as the transitions within the samples with variation in temperature. Structural analysis of the samples was carried out using X-ray diffraction (XRD). XRD revealed that all the samples possess hexagonal structure with space group P63/mmc. AC electrical properties including dielectric constant (έ), dielectric loss tangent (tan δ) and ac electrical conductivity (σ ac ) were studied as a function of frequency (1 kHz–3 MHz) at temperatures 100–700 °C. The dielectric losses tend to decrease with increasing Cr content. AC conductivity could be very well explained by Jonscher power law. These materials have applications in high frequency devices with reduced energy losses.

Structural, dielectric and magnetic properties of Cr–Zn doped strontium hexa-ferrites for high frequency applications

M-type strontium hexa-ferrite nano particles with composition SrFe12−2xCrxZnxO19 (X=0.0, 0.2, 0.4, 0.6, 0.8) were prepared by co-precipitation method and are reported for the first time. X-ray diffraction analysis confirmed the successful substitution of Cr and Zn ions in the strontium hexa-ferrite lattice. Structural morphology studied by scanning electron micrographs revealed that Cr–Zn doping inhabits the grain growth. Dielectric measurements were taken as a function of frequency in the range (10kHz to 3MHz). Both dielectric constants and dielectric losses were found to be decreasing with the increase in Cr–Zn concentration. As Cr–Zn doping favored the decrease in dielectric losses to a large extent (0.32–0.02) so the strontium hexa-ferrite with these dopants is very useful for high frequency applications. The frequency dependent ac conductivity increases sharply at higher frequencies due to increase in hopping frequency of electrons and decrease with the increase in doping concentration and this is due to decrease in Fe2+ ions. Temperature dependent dc electrical resistivity measurements showed a decreasing trend with the increase in Cr–Zn concentration. The M–H loop indicated that both coercivity and saturation magnetization were decreased with the increase in doping concentration. The former was decreased due to increase in grain size and later was decreased due to weak and non-magnetic cations distribution on interstitial sites.

Formation of a magnetic composite by reduction of Co-Nd doped strontium hexaferrite in a hydrogen gas flow

Co-Nd strontium hexaferrite nanoparticles synthesized by the self-combustion method were treated in a hydrogen flow at different temperatures and times. The samples were characterized structurally by scanning electron microscopy and X-ray diffraction and magnetically with a vibrating sample magnetometer. Phase identification showed decomposition of the hexaferrite structure into Fe3O4 and different strontium mixed oxides. The sample treated at 500°C for 30minutes shows good magnetic properties due to the formation of a magnetite/hexaferrite composite. In this case magnetization is very close to the original sample while the coercivity slightly diminishes. The hexagonal phase is almost completely transformed into different oxides at a reducing temperature of 500°C for 120minutes. The obtained results are analyzed in terms of the phase composition and of the magnetic susceptibility of the studied samples.

Magnetic properties of Sn–Mg substituted strontium hexaferrite nanoparticles synthesized via coprecipitation method

Nanoparticles of Sn–Mg substituted strontium hexaferrite with the composition of SrFe 12− x (Sn 0.5 Mg 0.5) x O 19 ( x = 0.0–1.0) were synthesized by chemical coprecipitation method. Deionized water/ethanol (50/50) was used as the solvent. The single phase strontium hexaferrites were obtained at pH 13 and Fe 3+/Sr 2+ molar ratio of 9 after calcination at 800 °C. The mean particle size of samples was decreased from 82 to 56 nm with increasing the Sn–Mg content from x = 0.0 to x = 0.8. The effect of Sn–Mg substitution on magnetic properties of hexaferrites was studied using vibrating-sample magnetometer. It was found that increasing the Sn–Mg from x = 0.0 to x = 0.8 reduced the coercivity from 4728.9 to 1455.5 Oe and increased the saturation magnetization from 51.34 to 65.49 emu/g. A vector network analyzer was used to investigate the microwave absorption properties. According to microwave measurements, doped strontium hexaferrite composites had much more effective electromagnetic absorption properties than undoped strontium hexaferrite composite.

Temperature dependence of magnetic properties of zinc and niobium doped strontium hexaferrite nanoparticles

Zinc and niobium doped strontium hexaferrite nanoparticles, Sr(Zn0.7Nb0.3)xFe12−xO19 (x=0–1.0), were fabricated using a sol-gel method for high density magnetic recording. The structure and temperature dependence of magnetic properties are investigated. The experiments show that strontium hexaferrite with small Zn and Nb substitutions still remains a hexagonal magnetoplumbite phase. The coercive force is reduced from 6.7 to about 2.3 kOe, while the values of saturation magnetization increased to 67–74 emu/g in the substitution range of x=0–1.0. This indicates that the saturation magnetization and coercivity of strontium hexaferrite nanoparticles can be held over a very wide range by an appropriate amount of Zn and Nb doping contents. Simultaneously, it is found that the doped strontium hexaferrite nanoparticles show a small positive temperature coefficient of coercivity. The substitution of Zn2+ and Nb4+ ions for Fe3+ ions also monitors the temperature dependence of magnetization and Curie temperature, and enhances thermal stability in the measured temperature range. This nanoparticle system is, thus, suitable for high-density recording.