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The sol gel method has been adopted to synthesize a series of X-type hexagonal ferrites with concentration Sr 2− x Gd x Ni 2 Fe 28− y Cd y O 46 ( x =0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and y =0, 0.1, 0.2, 0.3, 0.4, 0.5). The XRD analysis reveals the single phase of the prepared material and the lattice constants a (Å) and c (Å) varies with additives. The crystallite size of the present investigated ferrite is found in the range of 20–30 nm measured from TEM image. The enhancement in the magnetic properties (saturation magnetization, remanance magnetization and coercivity) can be observed with the increase of dopping concentration and the coercivity lies in the range of (484.22–887.47) G. The saturation and remanance magnetization decreases monotonically with the temperature which is the characteristic of the hexagonal ferrites. The Gd–Cd substituted sample possesses low values of complex relative permittivity and permeability than the pure samples. The material exhibits maximum microwave absorption −23 dB at 11.87 GHz and attenuation peak is in good agreement with the reflection loss value. The microwave absorption properties reflect the applications of this material in super high frequency devices (SHF). [ABSTRACT FROM AUTHOR]

The effect of rare earth elements substitution in Sr 1.96 RE 0.04 Co 2 Fe 27.80 Mn 0.2 O 46 (RE=Ce, Gd, Nd, La and Sm) X-type hexagonal ferrites prepared by using sol gel autocombustion method was studied. The XRD and FTIR analysis show the single phase of the prepared material. The lattice constants a (Å) and c (Å) varies with the additives. The particle size measured by Scherer formula for all the samples varies in the range of 54–100 nm and confirmed by the TEM analysis. The average grain size measured by SEM analysis lies in the range of 0.672–1.01 µm for all the samples. The Gd-substituted ferrite has higher value of coercivity (526.06 G) among all the samples which could be a good material for longitudinal recording media. The results also indicate that the Gd-substituted sample has maximum reflection loss of −25.2 dB at 11.878 GHz, can exhibit the best microwave absorption properties among all the substituted samples. Furthermore, the minimum value of reflection loss shifts towards the lower and higher frequencies with the substitution of rare earth elements which confirms that the microwave absorption properties can be tuned with the substitution of rare earth elements in pure ferrites. The peak value of attenuation constant at higher frequency agrees well the reflection loss data. [ABSTRACT FROM AUTHOR]

In order to understand the substitutional effect of rare earth element Sm 3+ and divalent Mn 2+ on structural, magnetic and microwave absorption properties of hexagonal ferrites, a series of Sr 2− x Sm x Ni 2 Fe 28−y Mn y O 46 X-type hexagonal ferrites with concentration ( x =0.00, 0.02, 0.04, 0.06, 0.08, 0.10 and y =0, 0.1, 0.2, 0.3, 0.4, 0.5) was synthesized by the sol–gel method. The XRD analysis shows that the material crystallized into single X-type hexagonal phase. The absorption bands at low wave number in FTIR curves are the characteristics of the X-type hexagonal ferrites. Decreasing trend in the magnetic properties with the substitution of Sm–Mn contents was also observed, which may be attributed to the oxidation of Mn 2+ ions into Mn 3+ ions and spin canting effect of rare earth element Sm 3+ . The reflection loss peak shifted towards the low frequency and microwave absorption properties of the material enhanced with the substitution of Sm–Mn contents which reflects its applications in super high frequency (SHF) devices. The attenuation constant curves are in good agreement with the reflection loss peak. [ABSTRACT FROM AUTHOR]

A series of single phase spinel ferrites having chemical formula Mg 0.5 Zn 0.5 Pr x Fe 2− x O 4 ( x =0.00, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared using the sol–gel technique after sintering at 700 °C. The thermal decomposition behavior of an as prepared powder was investigated by means of DTA/TGA analyses. The sintered powders were then characterized by Fourier transform infrared spectroscope, X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope and vibrating sample magnetometer. X-ray diffraction patterns confirm the single phase spinel structure of prepared ferrites without the presence of any impurity phase. The value of lattice parameter ( a ) increases with the increase of Pr contents ( x ) into the spinel lattice. The grain size estimated from electron microscope images is in the range of 2.75–5.4 µm which confirms the spinel crystalline nature of the investigated samples. The saturation magnetization ( M s ) decreases whereas coercivity ( H c ) increases with the increase of Pr contents ( x ). The measured parameters suggest that these materials are favorable for high frequency applications and as core materials. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic and microwave characterization of single phase hexaferrites of entirely new composition Ba1-x Sr x Co2AlFe15O27 (x=0.2–1.0) for application in a microwave absorber, have been reported. The samples synthesized by sol–gel method were investigated by differential thermal analyzer, Fourier transform infrared spectroscope, X-ray diffractometer, field emission gun scanning electron microscope, vibrating sample magnetometer and vector network analyzer. Platelet grains exhibit well defined hexagonal shape which is a better shape for microwave absorption. M–H loops for a selected sample were measured for a temperature range of 4.2–400K. Moreover M–H loops for all Sr-substituted samples were also measured at room temperature up to a maximum applied field of 9T. Saturation magnetization values were calculated by the law of approach to saturation. The room temperature coercivity for all the samples is found to be a few hundred oersteds which is necessary for electromagnetic materials and makes these ferrites ideal for microwave devices, security, switching and sensing applications. The complex permittivity, permeability and reflection losses of a selected ferrite–epoxy composite were also investigated over a frequency range of 0.5–13GHz. [Copyright &y& Elsevier]

Abstract: CoHo x Fe2−x O4 ferrites (x=0.00–0.1) were prepared by the co-precipitation technique and the effect of holmium substitution on the magnetic properties was investigated. X-ray diffraction reveals that the substituted samples show a second phase of HoFeO3 along with the spinel phase. The magnetic properties such as the saturation magnetization (M s ), coercivity (H c ) and remanence (M r ) are obtained from the hysteresis loops. It is observed that the M s decreases while H c increases with Ho3+ substitution. The decrease of saturation magnetization is attributed to the weakening of exchange interactions. The coercivity increases with increase of the Ho3+ concentration, which is attributed to the presence of an ultra-thin layer at the grain boundaries that impedes the domain wall motion. Low field AC susceptibility was also measured over the temperature range 300–600K at the frequency of 200Hz. It decreases with the increase of temperature following the Curie–Weiss law up to the Curie temperature. Above the Curie temperature it shows paramagnetic behavior. The increase in coercivity suggests that the material can be used for applications in perpendicular recording media. [Copyright &y& Elsevier]