Tunable heat generation in nickel-substituted zinc ferrite nanoparticles for magnetic hyperthermia.

We report a high-performance magnetic nanoparticle as a hyperthermic agent under low applied field and frequency. CTAB (cetyltrimethylammonium bromide)-coated Ni x Zn 1- x Fe 2 O 4 nanoparticles of average particle size < 25 nm with various stoichiometric ratios were successfully synthesized using a co-precipitation technique. Characterization results indicate a close interaction of CTAB ions with the surface metal ions resulting in a cation distribution deviating from their equilibrium positions. Magnetic measurements were done at 300 K and 5 K using a superconducting quantum interference device. Saturation magnetization gradually increases with increasing substitution of Ni 2+ ions with Zn 2+ ions, attributed to the cation distribution and high super-exchange interaction between the A- and B-sites. The average size of the nanoparticles is estimated to be <10 nm with a magnetically dead layer (>1 nm @ 300 K), reflecting the effect of CTAB coating on the surface of the nanoparticles. The magnetocrystalline anisotropy ( K eff ), obtained from the law of approach to saturation, is inversely proportional to the M s value. The increasing incorporation of Ni 2+ ions in the lattice system is found to influence various structural parameters, which is reflected in the magnetic performance of the nanoparticles. A specific absorption rate of 347 W g -1 and intrinsic loss power of 4.6 nH m 2 kg -1 was attained with a minimal concentration of 2 mg ml -1 in a very short time period of 1.5 min in Ni 0.75 Zn 0.25 Fe 2 O 4 nanoparticles.