Reaction kinetic, magnetic and microwave absorption studies of SrFe_11.2Ni _0.8O₁₉ hexaferrite nanoparticles

Abstract

Nickel substituted strontium hexaferrite, SrFe_11.2Ni _0.8O₁₉ nanoparticles having super paramagnetic nature were synthesised by co-precipitation of chloride salts using 7.5 M sodium hydroxide solution. The resulting precursors were heat treated (HT) at 900 and 1,200 °C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as a constant rate of nucleation and three dimensional growth with activation energy of 183.724 kJ/mole. The hysteresis loops showed an increase in saturation magnetization from 1.045 to 65.188 emu/g with increasing HT temperatures. The ‘as-synthesised’ particles have size in the range of 20–25 nm with spherical and needle shapes. Further, these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plates with increase in HT temperatures. The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permitivity and permeability) and microwave absorption properties were estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite powder reaches −24.92 dB at the thickness of 2.2 mm which suits its application in RADAR absorbing materials.