Effect of Ni–Zr codoping on dielectric and magnetic properties of SrFe12O19 via sol–gel route

• The substitution of Ni2+ and Zr4+ causes grain coarsening.
• Hc decreases due to microstructural and grain size variation.
• Ms is enhanced (x=0.4) due to replacement of Fe3+ ions.
• The ε′ and ε″ decreases with Ni–Zr substitution.
• In μ′, the relaxation frequency is observed above 1 GHz for all samples.

Nanocrystalline strontium hexaferrites [SrFe12–2x (Ni2+–Zr4+)xO19] nanoparticles were successfully synthesized by sol–gel process. For densification the powders were sintered at 950 °C/4 h. The sintered samples were characterized by X-ray diffraction (XRD), surface area measurement, and field emission scanning electron microscope (FESEM). The lattice parameter a is almost constant but c increased with x upto 0.8 and then decreased. The frequency dependent complex permittivity (ε′ and ε″) and permeability (µ′ and µ″) and magnetic properties such as saturation magnetization (Ms), coercive field (Hc) were studied. It is observed that saturation magnetization increased gradually from 57.82 emu/g to 67.2 emu/g as x increased from 0.2 to 0.4 and then decreased from 67.2 emu/g to 31.63 emu/g for x=1.0. In present study, x=0.4 shows high value of Ms 67.2 emu/g. The real part of permittivity (ε′) remains constant upto a frequency 1 GHz and increases further with an increase of frequency, a resonance and anti-resonance peak was observed above 1 GHz for all the samples. In real part of permeability (μ′) the relaxation frequency is observed above 1 GHz for all the samples and it is attributed to the domain wall motion. It is well known that the permeability for polycrystalline ferrites can be described as the superposition of two different magnetizing mechanisms: spin rotation and domain wall motion. These low coercive strontium hexaferrites are suitable for magnetic recording applications in hard disks, floppy disks, video tapes, etc.

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