resumo
Mg substituted X-type hexagonal ferrites with the chemical composition Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were successfully synthesised by a sol-gel auto-combustion technique, in order to investigate the effect of Mg substitution on structural, magnetic and dielectric properties. XRD analysis of prepared samples revealed the formation of pure X-type phase. The variations (decreasing trend) in lattice parameters with Mg substitution indicate the incorporation of Mg substitution into the crystal structure. The average crystallite size of heated powders was found to be in the range of 16-22 nm. For the first time, the RT hysteresis loops of Ba2Zn2Fe28O46 (Zn2X), Ba2Mg2Fe28O46 (Mg2X) and Ba2Zn2-xMgxFe28O46(x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were measured. The saturation magnetisation showed an initial decrease with x = 0.4-1.2, and then an increase with x > 1.2, to the largest final values of 63.29 Am-2 kg(-1) for the fully Mgesubstituted x = 2.0. The value of coercivity lies in the range of 89.9-209.3 kAm(-1) (1130-2630 Oe), and the magnetic results suggest that the compositions x = 0.0, 0.4 and 1.2 possess multi-domain microstructures, while x = 0.8, 1.6 and 2.0 possess single domain microstructures. The room temperature M.ssbauer spectra were analysed with six sextets of five magnetic sublattices, and the results are presented as a function of Mg substitution. It was found that initial levels of Mg substitution reduce the Fe populations at a and b (spin up) sublattices, but that with x > 1.2 these become repopulated at f(IV) (spin down) site, resulting in an increase in magnetisation. Dielectric parameters such as dielectric constant and loss factor were studied as a function of frequency, and results show normal behaviour for ferrimagnetic materials. At low frequencies (100 Hz-2 MHz), relative permittivity was constant between 0.3 and 1.5 above 20 kHz, with the higher values belonging to the more dense samples. All Mg substituted samples had lower losses above 20 kHz than the pure Zn2X. In complex measurements at microwave frequencies (500 MHz-13.5 GHz), all samples had a real permittivity of around 7.5, except for the fully Mgesubstituted sample (x = 2.0), which had a lower epsilon' of 5.5. For two samples (x = 0.4 and 1.6) we observed dielectric resonances between 12.85 and 13.25 GHz. All showed a steady real permeability of around 1.2-1.5 over the whole 1-13 GHz range, and ferromagnetic resonance (FMR) between 1 and 5 GHz, and similar to 12.5 GHz. (c) 2018 Elsevier B.V. All rights reserved.
palavras-chave
W-TYPE; ELECTROMAGNETIC PROPERTIES; STRONTIUM HEXAFERRITE; HEXAGONAL FERRITES; COMBUSTION ROUTE; MICROWAVE; MOSSBAUER; SRFE12O19; BA2CO2FE28O46; DISPERSION
categoria
Chemistry; Materials Science; Metallurgy & Metallurgical Engineering
autores
Kagdi, AR; Solanki, NP; Carvalho, FE; Meena, SS; Bhatt, P; Pullar, RC; Jotania, RB
nossos autores
Rob Pullar
Colaboradoragradecimentos
This work was supported by DRS-SAP (Phse-I) programme of UGC (No. UGC-F.530/10/DRS/2010 (SAP-I)), New Delhi, India and DST-FIST programme, India. One of the authors (Amrin R. Kagdi) acknowledges Ministry of Minority Affairs, Govt. of India for providing Maulana Azad National Fellowship (No. F1-17.1/2013-14/MANF-2013-14-MUS-GUJ-28541). R.C. Pullar wishes to thank FCT grant IF/00681/2015 for funding, and FCT Portugal-India Bilateral Action 2013-2016 and CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013) financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement, for supporting this work.