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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]