Investigation on crystallinity and optical properties of l-tartaric acid single crystal at dynamic shocked conditions

Journal of Materials Science: Materials in Electronics - In this article, the authors demonstrate the experimental findings of the effect of dynamic shock waves on the crystallographic structural...     

Temperature dependence of coercivity at recording frequencies:barium ferrite versus oxide

It is demonstrated that materials with comparable thermal dependence of coercivity under normal laboratory measurement conditions, differing only in sign, have quite different properties at recording frequencies. Barium ferrites, with positive dH_c/dT, have augmented thermal dependence, whereas oxides with negative dH_c/dT exhibit weaker thermal dependence at recording frequencies. Experimental data and theoretical analysis confirm this behavior. Two methods of predicting coercivity as a function of temperature, for recording time scales, are presented. The implications for direct overwrite performance while thermally cycling are discussed     

Magneto-optical properties of barium ferrite sputtered films

Barium ferrite thin films with perpendicular anisotropy were grown on (111) oriented GGG substrate by rf diode sputtering method. Their magnetic properties were measured. Faraday rotation was measured in the wavelength range 460–800 nm for such sputtered thin films. These films were found quite suitable for magneto-optical recording applications.     

Low temperature thermal expansion of barium ferrite

The linear thermal expansion of polycrystalline barium ferrite, BaFe₁₂O₁₉, was measured from 76 to 293 K both parallel and perpendicular to the magnetization direction. An anisotropy of about 15–20% was observed. The results match well with the available data above room temperature and have also been extrapolated to O K.     

Picosecond-pulse and millimeter-wave spectroscopy of barium ferrite

Transmission measurements of a barium ferrite pressed-powder sample have been made with an optically switched picosecond-pulse spectrometer. By comparison to millimeter-wave spectroscopy of the same sample, features related to the ferrimagnetic resonance have been identified in the pulse spectrum. Time-domain spectra predicted from models of the permeability indicate significant discrepancies with the experimental short-pulse line shape     

Morphology control of barium ferrite thin films

Hexagonal barium ferrite thin films were fabricated by spin coating of precursors obtained by sol-gel methods onto sapphire (00l) faces. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used to tune the morphology of the films. The films show texture with c-axis normal to the film plane as shown by the strong x-ray diffractions from the (001) plane with full width at half maximum of the rocking curves about 0.4°. The [100] direction of the film is parallel to the [110] direction of the sapphire. With the increase of the citric acid, the percentage of the acicular crystallites increased. EDTA can be used to produce films with the best texture where faceted grains were obtained. The maximum coercive force obtained was about 302 kA/m.     

Characteristics of barium ferrite tape for magnetic contactduplication

The magnetic properties and electromagnetic characteristics of Ba-ferrite tape for R-DAT magnetic contact duplication (MCD) were investigated. The tapes employed Ba-ferrite particles averaging 0.06 μm in diameter with an aspect ratio between 4 and 5. Ba-ferrite tapes were prepared with perpendicular, longitudinal, and no orientation, and their MCD and ring-head recording (RHR) characteristics were compared. Several distinctive characteristics were observed in MCD, and the desirability of perpendicular orientation at short wavelengths in MCD applications is clear. Tilted orientation was also investigated, and its output level was similar to that of perpendicular orientation in MCD, while in RHR it proved superior to perpendicular orientation in the short wavelength region. The magnetization mode of the slave tape was studied by waveform analysis using the FFT method and in conjunction with the tapes' magnetic properties, such as uniaxial anisotropy energy, remanence coercivity, and squareness ratio     

Synthesis and characterization of barium ferrite–silica nanocomposites

In this work, we prepared barium ferrite-silica (BaM-SiO₂) nanocomposites of different molar ratios by high-energy ball milling, followed by heat-treatment at different temperatures. The microstructure, morphology and magnetic properties were characterized for different synthesis conditions by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results indicate that 15 h of milling was enough to avoid the generation of hematite phase and to get a good dispersion of barium ferrite particles in the ceramic matrix. For milling periods beyond 15 h and heat treatment above 900 °C, the XRD patterns showed the presence of hematite phase caused by the decomposition of BaM. The agglomerate size observed through SEM analysis was around 150 nm with a good BaM dispersion into the SiO₂ matrix. The highest saturation magnetization (Ms) value obtained was 43 emu/g and the corresponding coercivity (Hc) value of 3.4 kOe for the composition 60BaM-40SiO₂ milled for 15 h and heat treated at 900 °C. This coercivity value is acceptable for the application in magnetic recording media.     

The effects of magnetic quenching on glassy barium ferrite

Barium ferrite (BaFe₁₂O₁₉) prepared by solution evaporation techniques from ethylene glycol/citric acid or ethylene glycol/pyridine-1-oxide solutions is initially obtained in a glassy form. Although visual observations on samples heated to 1250° C showed that transparency was maintained in thin sections, X-ray powder diffraction studies showed the development of ordered regions of BaFe₁₂O₁₉. Prolonged heating at 1250° C resulted in a loss of visual transparency. Samples of partially amorphous material cooled rapidly in a weak magnetic field were found to have a magnetization considerably higher than samples cooled in the absence of a field. Samples rendered polycrystalline by heating for extended periods at 1250° C showed a lower magnetization on magnetic quenching.     

Ball milling of barium ferrite in air and vacuum

The effects of prolonged milling in air and vacuum on BaFe₁₂O₁₉ ionic crystal structure and particles morphology have been analysed. X-ray diffraction, scanning electron microscopy and thermal analysis experiments show that for vacuum-milled material the ordered structure transforms progressively into a stable disordered nanocrystalline phase. For air-milled samples, apart from structural transformation, chemical decomposition was found.     

Hydrothermal synthesis of barium ferrite fine particles from goethite

Barium ferrite fine particles were prepared from aqueous suspensions containing goethite (-FeOOH) and barium hydroxide by a hydrothermal method. Barium ferrite particles of thin hexagonal plate shape could be produced from commercially available goethite with an Fe: Ba molar ratio of 7.2, whereas barium ferrite particles could be produced from synthesized goethite with a molar ratio of unity. The effects on the size of hexagonal platelike particles of such reaction conditions as temperature, stirring speed and alkali concentration were investigated. Particles of 0.6 to 0.8 m mean size were prepared under the reaction conditions covered here.     

Synthesis of ultrafine particles of barium ferrite by chemical coprecipitation

A new method to synthesize barium hexaferrite by chemical coprecipitation is described. A mixed precursor was precipitated by addition of a barium salt to a strongly alkaline ferrate (VI) solution. The precursor yielded barium hexaferrite on heating for 6 h at 800 °C; partial transformation was evident even at lower temperatures, from X-ray patterns and Mossbauer spectra. Scanning electron microscopy of the powders fired at 800 °C, showed that the particles were less than 0.5 μm in diameter. This revised version was published online in November 2006 with corrections to the Cover Date.     

Nanowires of NiCo/barium ferrite magnetic composite by electrodeposition

Electrodeposition has been demonstrated to be useful in preparing well defined composite nanowires and as a way to modify their magnetic properties. A sulphamate bath containing barium ferrite nanoparticles has been used to test nanoparticle incorporation during an alloy (NiCo) electrodeposition process. The nanoparticles enter the membrane pores during the electrodeposition, being uniformly distributed into them.Home-made alumina membranes prepared in the laboratory were used as an electrodeposition template. Composite 10–15 μm length nanowires containing 7 wt.% of ferrite with a good particle distribution were obtained. The formation of composite nanowires has been demonstrated both by TEM observation and by magnetic properties analysis. The feasibility of incorporating magnetic nanoparticles to metallic nanowires in order to modify their magnetic properties has thus been confirmed.     

Development of millimeter wave integrated circulator based on barium ferrite

The development of telecommunications networks requires low-cost microwave and millimeter waves integrated devices. Among the microwave devices based on the non-reciprocity of ferrites, circulators are the most important. A typical use of circulators is in communication equipment (mobile phone and low power radar detection). Their operation allows to combine emission and detection using the same antenna. This work concerns the characterization of barium hexaferrite sputtered films and the device integration for the development of an integrated circulator working at a frequency of 40 GHz.     

M型钡铁氧体制备及吸波特性研究

为进一步研究M型铁氧体的吸波性能,以硝酸铁、硝酸钡为原料,采用溶胶凝胶自蔓延法,制备了M型钡铁氧体纳米粉.借助XRD、TG-DTA、SEM、矢量网络分析仪对铁氧体材料的晶体结构、凝胶热分解过程、表面形貌及微波吸收特性进行了研究,同时根据传输线原理,通过理论计算预测了材料的最佳匹配厚度.研究表明:所制得的铁氧体为晶相单一的M型钡铁氧体,频率在6～18GHz,预测最佳匹配厚度为0.35cm,最小反射损耗达-13.5dB,反射损耗小于-10dB的带宽为0.7GHz,说明M型钡铁氧体具有电磁波吸收效应.     

On the magnetic properties of fine-milled barium and strontium ferrite

The temperature dependence of the specific saturation magnetization of barium and strontium ferrite powders after milling in an attrition mill has been investigated at temperatures between -195°C and the Curie temperature of the ferrites. The experimental results show that the specific saturation magnetization decreases with increasing milling time and that a second, presumably soft-magnetic phase occurs during milling which vanishes during annealing of the powders. The influence of lattice defects introduced by the milling process is discussed.     

Static and dynamic magnetic properties of Co<Subscript>2</Subscript>Z barium ferrite nanoparticle composites

The static, dynamic and attenuation properties of Co₂Z barium ferrites and Co₂Z composites have been studied. The results showed that both static and dynamic magnetic properties are significantly different for large particles and nanoparticles. As compared to large particles, Co₂Z nanoparticles have a small saturation magnetization M_s, large coercivity H_c, small permeability ₀ and _max, but high resonance frequency f_R. The maximum reflection loss predicted is much smaller for nanoparticles than for large particles. Therefore, Co₂Z barium ferrite with large particle is more suitable for EM materials with high attenuation and broad bandwidth at microwave frequency.     

Effect of boric acid sintering aid on densification of barium ferrite

Boric acid has been added in 0.1-0.6% range for studying the densification characteristics of solid state sintered barium hexaferrite. Sintering studies have been carried out at three different temperatures. Physical properties like density and porosity have been studied for all compositions. The phase identification and microstructural investigation on the fractured surface have been carried out to understand the effect of sintering aid on the densification characteristics.