Development of hard/soft ferrite nanocomposite for enhanced microwave absorption

Nickel and zinc substituted strontium hexaferrite, SrFe(11)Zn(0.5)Ni(0.5)O(19) (SrFe(12)O(19)/NiFe(2)O(4)/ZnFe(2)O(4)) nanoparticles having super paramagnetic nature are synthesized by co-precipitation of chloride salts using 7.5 M sodium hydroxide solution. The resulting precursors are heat treated (HT) at 900 and 1200 degrees C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as a constant rate of nucleation and three dimensional growth with an activation energy of 176.79 kJ/mol. The hysteresis loops show an increase in saturation magnetization from 1.042 to 59.789 emu/g with increasing HT temperatures. The 'as-synthesized' particles with spherical and needle shapes have size in the range of 20-25 nm. Further, these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plate and pyramidal shapes with increase in HT temperatures. The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permittivity and permeability) and microwave absorption properties are estimated in X band (8.2-12.2 GHz). The maximum reflection loss of the composite reaches -29.62 dB (99% power attenuation) at 10.21 GHz which suits its application in RADAR absorbing materials. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.