Microwave absorption studies of magnetic sublattices in microwave sintered Cr3+ doped SrFe12O19

Abstract

The partial substitution of Fe3+ by Cr3+ in strontium hexaferrite has shown to be an effective method to tailor anisotropy for many novel microwave applications. Some basic studies have revealed that this substitution leads to unusual interactions among the magnetic sublattices of the hexaferrite. In order to investigate these interactions, Cr3+ doped SrCrxFe12−xO19 (x=0.0, 0.1, 0.3, 0.5, 0.7 and 0.9) (m-type) hexaferrites were prepared by microwave-hydrothermal (m-H) method and subsequently sintered at 950°C/90min using microwave furnace. The magnetic hysteresis (m-H) loops revealed the ferromagnetic nature of nanoparticles (NPs). The coercive field was increasing from 3291Oe to 7335Oe with increasing chromium content. This resulting compacts exhibited high squareness ratio (Mr/Ms–80%). The intrinsic coercivity (Hci) above 1,20,000Oe and high values of magnetocrystalline anisotropy revealed that all samples are magnetically hard materials. A material with high loss as well as high dielectric constant may be desired in applications such as electromagnetic (EM) wave absorbing coatings. The room temperature complex dielectric and magnetic properties (ε′, ε′′, µ′ and µ′′) of Cr3+ doped SrFe12O19 were measured in X-band region. The frequency dependent dielectric and magnetic losses were increasing to large extent. The reflection coefficient varied from −16 to −33dB at 10.1GHz as Cr3+ concentration increased from x=0.0 to x=0.9. Ferromagnetic resonance spectra (FMR) were measured in the X-band (9.4GHz), linewidth decreases with chromium concentration from 1368 to 752Oe from x=0.0 to x=0.9, which is quite low compared to commercial samples. We also have detailed origins of the FMR linewidth broadenings in terms of some important theoretical models. These results show that chromium doped strontium hexaferrites are useful for microwave absorption in the X-band frequency and also have potential for use in low frequency self-biased microwave/millimeter devices such as circulators and isolators.