Structural, magnetic and microwave absorption properties of doped Ba-hexaferrite nanoparticles synthesized by co-precipitation method

Magnetic, dielectric and microwave properties of M–Ti substituted barium hexaferrites (M=Mn2+, Co2+, Cu2+, Ni2+, Zn2+)

Magnetic and microwave properties of BaFe12O19 substituted with magnetic, non-magnetic and dielectric ions

M-type barium ferrite powders doped with Zr4+ ions (BaFe12−xZrxO19x = 0–0.4), possessing high permittivity and multi-resonant permeability, were synthesized by the sol–gel process. The single-phase hexagonal plate-like barium ferrites were formed with Zr4+ substituting Fe3+ at the 4f1 sites initially and then at the 2b sites afterwards with increasing doping content. The Ha of the ferrites decreased from 15.75 kOe to 8.13 kOe with increasing Zr4+ from x = 0 to 0.4. The e′ and e′′ of the ferrite with Zr4+ doping were increased to 7.7–6 and 3.4–1.5 over 18–40 GHz from 5.8–5 and 0.7–0.4 without doping, respectively. Contributed mainly by the enhanced permittivity, the matching thicknesses of the Zr4+ ions doped ferrites were as low as only ∼1 mm or below, i.e. 1.5–3 times thinner than those reported recently. The complex permittivity was still close to the complex permeability in the doped ferrites. Hence, a strong reflection loss of ∼−50 dB could be attained and the absorptivity of electromagnetic (EM) power per unit thickness reached as high as 0.156% μm−1, i.e. 2–5 times higher than those of novel absorbing materials. The multi-resonance permeability peaks originated from Fe3+ ions, and exchange couplings among Fe3+, Fe2+ and O− contributed multiple reflection loss peaks and thus, a broad bandwidth of ∼12 GHz (RL < −10 dB), which was 2–4 times broader than those normally reported. Consequently, the Zr4+-doped barium ferrites are promising for use as excellent absorbing materials in the millimeter wavelength frequency range.

Zr4+ doping-controlled permittivity and permeability of BaFe12−xZrxO19 and the extraordinary EM absorption power in the millimeter wavelength frequency range

Enhancement on the exchange coupling behavior of SrCo0.02Zr0.02Fe11.96O19/MFe2O4 (M = Co, Ni, Cu, Mn and Zn) as hard/soft magnetic nanocomposites

Nanoparticles of the giant dielectric material, calcium copper titanate from a sol–gel technique

Nano-sized calcium copper titanate (CCTO) powder was synthesized from a quick and innovative sol–gel process. Calcium nitrate, copper nitrate and titanium isopropoxide were used as the raw materials to synthesize the precursor product. The dried precursor powder was then milled and calcined at 450, 550, 650, 800, 850 and 950 °C for 3 h. The XRD results of the powder calcined at 800 °C indicates the formation of CCTO single phase. AFM studies shows that the average particle size of CCTO powder ranges around 80 nm. From the FTIR spectra the modes observed at 606, 525 and 463 cm−1 was assigned to vibration modes of Ca–O, Cu–O and Ti–O–Ti, respectively. The samples sintered at 1,040 °C shows high density (96%) as compared to the theoretical value. The grain sizes of sintered pellets were determined by FE-SEM and the dielectric properties were studied by LCR meter.

Phase formation and high dielectric constant of calcium copper titanate using sol–gel route

Structural and magnetic properties of conventional and microwave treated Ni-Zr doped barium strontium hexaferrite

CoFe2O4 ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe2O4 crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe2O4 samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe2O4 ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.

Synthesis of CoFe2O4 powder via PVA assisted sol–gel process

M-type Hexaferrites B0.5Sr0.5Fe12−2xNixZrxO19 were synthesized and investigated. The XRD patterns show single phase of the magnetoplumbite barium strontium ferrite and no other phases were present. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. As the substitution level increased from x = 0.2 to 0.8 mol%, the grains are agglomerated and the average diameter increased. This suggests that Ni–Zr substitution increases the grain size, as observed in the FE-SEM micrographs. The results of magnetic measurement revealed that Ms of barium strontium hexaferrite increased when the value of x increased from 0 to 0.4 mol% and then decreased with the increasing Ni–Zr content. The Hc decreases remarkably with increasing Ni and Zr ions content. Hard magnetic material is converted into soft magnetic material when the substitution level is increased from 0.2 to 0.8 mol%. In particular, Ba0.5Sr0.5Fe12−2xNixZrxO19 with x = 0.2, 0.4, 0.6, 0.8 mol% has suitable magnetic characteristics with particle size small enough for high-density magnetic recording applications.

R. Velmurugan

Papers

Nanoparticles of the giant dielectric material, calcium copper titanate from a sol–gel technique

Phase formation and high dielectric constant of calcium copper titanate using sol–gel route

Structural and magnetic properties of conventional and microwave treated Ni-Zr doped barium strontium hexaferrite

Synthesis of CoFe2O4 powder via PVA assisted sol–gel process

Preparation and magnetic properties of Ni–Zr doped barium strontium hexaferrite