Single Phase Strontium Hexaferrite Research Articles

Preparation, magnetic and photocatalytic properties of nano-structured SrFe12O19 obtained via an optimized mechano-thermal route using celestite ore

Nano-structured SrFe12O19 was synthesized from celestite ore, using two routes of the mechano-thermal method. Ball-milling was employed, and the thermal analysis data confirmed the mechanical activation. After calcination at 1000 °C, the results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated the formation of single-phase strontium hexaferrite with a mean particle size of 196 nm and plate-like hexagonal structure. The vibrating sample magnetometer (VSM) study exhibited the coercivity and saturation magnetization values of 4800 Oe and 63 emu/g, respectively. The diffusion reflectance spectroscopy (DRS) test displayed light absorption in the range of visible light with a band-gap energy value of 1.78 eV. As a photocatalyst, a degradation efficiency of 84% was obtained for an initial methylene blue concentration of 5 mg/L with a photocatalyst dosage of 4 g/L after 180 min of visible light irradiation. Also, the degradation mechanism and kinetics were described in detail. A study on the reusability and stability indicated good recyclability of the prepared powder during the cyclical degradation.

Investigation on the site preferences & magnetic properties of Co-doped SrAl4Fe8O19 hexaferrite

The present work describes the structural and magnetic properties of partially Co substituted SrAl4CoxFe8-xO19 (0.0≤ x ≤ 0.6) ferrites. Single-phase strontium hexaferrite (p63/mmc) was synthesized by the sol-gel auto combustion method. The structural studies were carried out by the Rietveld analysis to get the information about the substituted sites of transition metal ions, bond length, and bond angle. Types of the bond were also explored through FTIR. EDX elemental analysis and mapping had also verified the presence of single-phase strontium hexaferrite. The effect of Co ion substitution on the magnetic properties was investigated with the help of a magnetic property measurement system (MPMS). The relationship between the occupancy of transition metal ions over the five sub-lattice sites was analyzed. The magneto-crystalline anisotropy was analyzed from the “Law of Approach to Saturation magnetization (Ms)” method. The oxidation state of the Co ion was also examined by the XAS spectra. The substitution of Co+3 enhanced the magnetization and permeability of the ferrites. Results indicated the significant dependency of Co+3 ion on the magnetic properties of strontium hexaferrite.

Effect of Co and Sm Substitutions on the Magnetic Interactions of M-Type Strontium Hexaferrite Nanoparticles

In this contribution, we report the tuning of magnetic properties of Co- and Sm-substituted strontium hexaferrite nanoparticles. Stoichiometric and single-phase strontium hexaferrite (SrM) nanoparticles have been synthesised by sol–gel route using high-purity nitrates. The structural characterisation of synthesised samples was studied by X-ray diffraction studies. The experimental evidence indicates the crystallite size and morphology of nanoparticles. Hysteresis curves of Sr(1−x)SmxFe12O19 (x = 0.1, 0.2 and 0.3) show a significant increase of the coercivity of the samples, as compared with those of SrFe12−xCoxO19 (x = 0.1, 0.2 and 0.3), which depend on the effect of Fe2+ anisotropy on the 2a site in the Sm3+ ions. This effect if resulted in the large magneto crystalline anisotropy and coercive force. Important magnetic properties such as coercivity, remanence, saturation magnetisation, Bohr magneton and squareness ratio and exchange coupling can be tailored by controlling the grain size, composition and density of bulk magnetic materials. At nanometric length scales, the grain size plays an increasingly important role since magnetic domain behaviour and grain boundary concentration determine bulk magnetic behaviour. The temperature dependence magnetic behaviours of the samples were also discussed.

The effect of pH value on strontium hexaferrites: microstructure and magnetic properties

Well scattered strontium hexaferrites (SrFe12O19) nanoparticles have been successfully synthesized by coprecipitation method using polyvinyl alcohol (PVA) as a surfactant and calcinated at 850 °C. With the aim of exploring the magnetic properties of powders obtained, pH values ranging from 8 to 12. The resulting particles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Ultraviolet–Visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, dynamic light scattering and vibrating sample magnetometer. In the pH value range 8–12 inclusively, there is sharp rise in the coercivity but an evident decline in both the saturation and remanence magnetization. Fe2O3, as a secondary phase, was discovered to reduce and even disappeared in higher pH value. Single phase strontium hexaferrite plates roughly 40 nm in size were synthesized at pH = 12, and the resulting powders present a coercivity being as high as 4321 Oe and a weak saturation magnetization. Comparing magnetic property of as-obtained nanoparticles synthesized at low pH values, the material combined with higher pH and PVA is in pure phase, which may pave a way for large-scale application.

Facile sonochemical preparation and magnetic properties of strontium hexaferrite (SrFe12O19) nanoparticles

The hard magnetic material M-type strontium hexaferrite (SrFe12O19) was prepared by a facile surfactant-free sonochemical strategy and subsequently by a calcination process. The surface morphologies, structures, and Curie temperature of the obtained final product was investigated by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), BET (Brunauer–Emmett–Teller) specific surface area (SSA) and thermogravimetric analysis (TGA). XRD confirmed the formation of single-phase strontium hexaferrite with space group P63/mmc (194) and hexagonal structure and the mean primary crystallite size was found to be 44 nm. The morphology of synthesized SrFe12O19 product was in spherical shape with good crystalline nature. The measured Curie temperature (Tc) of the nanoparticles was around 462 °C. The magnetic property of the sample was measured by using a Superconducting Quantum Interference Device (SQUID) magnetometer at temperatures between 4 and 300 K. The measured saturation magnetization (Ms) at 300 K, 33 emu/g, is significantly lower than that found for bulk SrFe12O19, probably reflecting a size effect of the nano-particles.

Influence of metal precursor on the synthesis and magnetic properties of nanocrystalline SrFe12O19 thin films

The effects of metal precursor on the structure and magnetic properties of strontium hexaferrite (SrFe12O19) thin films synthesized by polymeric precursor method have been investigated. Fourier transform infrared, thermal analyses, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques were applied to evaluate the microstructure, composition, crystallite size and magnetic properties of the SrFe12O19 thin films. The films synthesized from metal nitrate precursor offered the single phase SrFe12O19 with the crystallite size of 42nm and isotropically magnetic properties of Ms=267emu/cm3, Mr=134emu/cm3, and Hc=4790Oe after calcination at 800°C. The films obtained from metal hydroxide and metal chloride precursors exhibited higher coercivities, 6063 and 5047Oe, respectively, due to the smaller particle size; however, they were not single phase strontium hexaferrite.

Synthesis and characterization of nanostructured strontium hexaferrite thin films by the sol–gel method

Nanostructured single phase strontium hexaferrite, SrFe12O19, thin films have been synthesized on the (100) silicon substrate using a spin coating sol–gel process. The thin films with various Fe/Sr molar ratios of 8–12 were calcined at different temperatures from 500 to 900°C. The composition, microstructure and magnetic properties of the SrFe12O19 thin films were characterized using Fourier transform infrared spectroscopy, differential thermal analysis, thermogravimetry, X-ray diffraction, electron microscopy and vibrating sample magnetometer. The results showed that the optimum molar ratio for Fe/Sr was 10 at which the lowest calcination temperature to obtain the single phase strontium hexaferrite thin film was 800°C. The magnetic measurements revealed that the sample with Fe/Sr molar ratio of 10, exhibited higher saturation magnetization (267.5emu/cm3) and coercivity (4290Oe) in comparison with those synthesized under other Fe/Sr molar ratios.

THE EFFECT OF HIGH ENERGY MILLING ON THE SR-HEXAFERRITE NANOCRYSTALLINE POWDER SYNTHESIZED BY A SOL-GEL AUTOCOMBUSTION METHOD

In this research SrFe 12 O 19 nanocrystalline synthesized by sol-gel auto-combustion method and subsequent annealing at 1000°C for 1h subjected to mechanochemical treatment in a high-energy ball mill and then re-annealing. A planetary ball mill (Fritsch Pulveristte 6) was used to mill the strontium hexaferrite powder at 300 rpm in air for 10, 20 and 40 hours. The process was studied by X-ray diffraction technique and scanning electron microscopy. The X-ray study showed that SrFe 12 O 19 phase was decomposed by milling. Strontium hexaferrite and α- Fe 2 O 3 were obtained with 10 hours milling. There were α- Fe 2 O 3 and strontium hexaferrite in XRD patterns of 20 hours milled sample. With increasing of the milling time to 40 hours, strontium hexaferrite was decomposed completely. The annealing of the 20 and 40 h milled powders at 900°C for 1h led to the formation of single phase strontium hexaferrite with smaller crystallite size compare to that of the hexaferrite powder before milling and subsequent annealing.

AN INVESTIGATION INTO MECHANOCHEMICAL SYNTHESIS OF NANOCRYSTALLINE HEXAFERRITE POWDER

Nanocrystalline strontium hexaferrite powder has been prepared by a new mechanochemical method in which the single phase hexaferrite was obtained via a sol–gel autocombustion process followed by an intermediate high energy milling step and subsequent annealing. The effects of the intermediate milling on the phase evolution, crystallite size and annealing behavior of the final products were investigated using the X-ray diffraction (XRD) technique. The single phase strontium hexaferrite was obtained at an annealing temperature of 800°C, while this temperature was 1,000°C for the powder synthesized without milling. It could be seen that an intermediate milling accelerates the formation of strontium hexaferrite during the calcination process. The results showed that in the milled powder, the average crystallite size of the ferrite was about 40 nm and much smaller than that of the nonmilled powder. Magnetic properties were also measured by a vibrating sample magnetometer (VSM). The particle morphology was then studied by scanning and transmission electron microscopes (SEM and TEM).

Fe/Sr ratio and calcination temperature effects on processing of nanostructured strontium hexaferrite thin films by a sol–gel method

Nanostructured single-phase strontium hexaferrite, SrFe12O19 (SrM), thin films have been synthesized successfully for the first time on silicon substrates using a spin-coating sol–gel process. The precursor solution was prepared from metal nitrates, citric acid, and ethylene glycol. The thin films with various Fe/Sr molar ratios of 8–12 were heat treated at different temperatures from 700 to 900 °C. The composition, microstructure, and magnetic properties of the SrM thin films were also characterized. The results showed that the optimum molar ratio for Fe/Sr was 10, at which the lowest calcination temperature for obtaining the single-phase strontium hexaferrite thin films was 800 °C. The crystallite size of the resultant thin films was below 50 nm.

Preparation of strontium hexaferrite magnets from celestite and iron ore fines by mechanochemical route

In the present investigation celestite and iron ore fines have been used for the preparation of strontium hexaferrite powder. The mechanical alloying process has been adopted to prepare strontium hexaferrite powder. The mixture of celestite after chemical upgradation and physically upgraded iron ore fines along with sodium carbonate was milled for different duration in a high energy planetary ball mill with tungsten carbide jar and ball to prepare strontium hexaferrite powder. A long duration of ball milling for different duration has led to solid-state displacement reaction. At the end of each experiment the product was washed thoroughly and dried. The X-ray diffraction study of milled powder after annealing shows the development of single phase strontium hexaferrite. The resultant powder was compacted under magnetic field and sintered to prepare the magnet after annealing the ferrite powder. The moderate value of coercivity, remanence and energy product were observed in this sintered magnet. The work illustrates the feasibility to prepare strontium hexaferrite magnetic powders directly from natural ores.

Conversion of Conventionally Synthesized Strontium Hexaferrite Powder Into a Nano Size Powder With Enhanced Coercivity Using GTMR Method

Strontium hexaferrite nanocrystalline powder was prepared by H2, CO and CH4 gas heat treatment and recalcination of the conventionally synthesized powder. The conventionally synthesized strontium hexaferrite was heated in hydrogen, carbon monoxide and methane dynamic atmospheres. This resulted in a change in magnetic nature of the material from hard to soft by decomposition of hexaferrite and reduction of the resultant iron oxide to the ultraflne grains of iron. Then the resultant powders calcined at 1000degC for 1 hour to form the single phase strontium hexaferrite again but with a nanocrystalline structure due to the formation of hexaferrite crystallites on the ultraflne grains of iron. In this work, the comparative effects of these processes on the phase evolution, morphology and size of the crystallites and magnetic properties were investigated by X-Ray Diffraction (XRD), Scanning and Transmission Electron Microscopy (SEM and TEM) and Vibration Sample Magnetometery (VSM) techniques. The results show a good enhancement in the magnetic properties particularly coercivity by applying this new method on the hexaferrite powder. Finally, the effect of milling process before recalcination on the magnetic properties has been investigated which shows a more significant improvement in the intrinsic coercivity of the initial material.

AN INVESTIGATION ON THE FORMATION OF STRONTIUM HEXAFERRITE NANO-POWDER BY A SOL-GEL AUTO-COMBUSTION METHOD IN THE PRESENCE OF SURFACTANT USING DIFFERENT BASIC AGENTS

Strontium hexaferrite is a hard magnetic material and has been extensively used as a permanent magnet. In this work a novel sol-gel auto-combustion method was used to synthesize ultra fine strontium hexaferrite. The investigations show that the model of combustion changes with the change of basic agent. The XRD results show that using ammonia or trimethylamine does not change the composition of the combustion product and it also shows that the surfactant burns completely during the combustion process. The average crystallite size of hexaferrite powders was also measured by X-ray line broadening technique employing Scherrer formula. The results show that changing the basic agent makes the particle size of the final product much smaller. Basic agent also affects the formation temperature of the single phase strontium hexaferrite.

Preparation of strontium hexaferrite nano-crystalline powder by carbon monoxide heat treatment and re-calcination from conventionally synthesized powder

In this work strontium hexaferrite nano-crystalline powders were prepared by carbon monoxide heat treatment and re-calcination from conventionally synthesized powder. First strontium hexaferrite was obtained by the conventional route with calcination of strontium carbonate and hematite at 1100 °C for 1 h. Then strontium hexaferrite was isothermally subjected to carbon monoxide dynamic atmosphere at various temperatures and flows for different times. Optimum carbon monoxide heat treatment was achieved at 850 °C with 20 cm 3 /min flow for 0.5 h. The resultant powder was then calcined at 900 and 1000 °C for 1 h. The single-phase strontium hexaferrite nano-crystalline powder was finally obtained after calcination at 1000 °C. The phase identification of the powders was recorded by an X-ray diffractometer (XRD) with Cu Kα radiation. Morphology and size of the particles were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The magnetic properties were also measured by a vibration sample magnetometer (VSM). The results show a good enhancement in the coercivity by applying this method on the hexaferrite powder.

Preparation of strontium hexaferrite magnets from celestite and blue dust by mechanochemical route

In the present investigation celestite (natural ore of strontium) and blue dust (iron ore fines) have been used for the preparation of strontium hexaferrite powder. The mechanical alloying process has been adopted to prepare strontium hexaferrite powder. The celestite after chemical upradation and physically upgraded blue dust alongwith sodium carbonate was taken for the preparation of strontium hexaferrite in this experiment. The high-energy planetary ball mill with tungsten carbide jar and ball was used to prepare strontium hexaferrite powder. A long time of ball milling for different duration has led to displacement solid-state reaction. At the end of each experiment the product was washed thoroughly and dried. The X-ray diffaction study after annealing shows the development of single-phase strontium hexaferrite after 40 hrs. of milling. The resultant powder was compacted under magnetic field and sintered to prepare the magnet after annealing the ferrite powder. The magnetic properties were measured by Pulse magneto meter. The moderate value of coercivity, remanence and energy product were observed in this sintered magnet. The work illustrates the feasibility to prepare strontium hexaferrite magnetic powders directly from natural ores which can reduce the total cost of production as compared to conventional method.

Optimization of the Fe/Sr ratio in processing of ultrafine strontium hexaferrite powders by a sol-gel autocombustion method

A novel sol-gel autocombustion method has been used to synthesize ultrafine particles of strontium hexaferrite. The nitrate citrate gels were prepared from metal nitrates and citric acid with various molar ratios of Fe/Sr. The results showed that the nitrate citrate gel exhibits a self-propagating behavior after ignition in air. The resultant powders with different molar ratios of Fe/Sr were investigated by the differential thermal analysis, thermal gravimetry, and X-ray diffraction techniques. The investigations showed that there was an optimum molar ratio for Fe/Sr in which the calcination temperature for obtaining single-phase strontium hexaferrite is minimum. Scanning electron microscopy was also used to characterize the microstructure of the products. The crystallite size of the resultant powder was about 40 to 50 nm.