Magnetic properties of nanoscale BaFe12O19 particles

Nanoscale BaFe(12)O(19) particles have been synthesized by citrate precursor technique. X-ray diffraction studies showed the formation of pure, fine grained, monophasic BaFe(12)O(19) particles and decrease in lattice parameters with the particle size. Magnetic clusters were observed by SEM and BET surface area measurements. Mossbauer results and the field dependence magnetic studies reveal the superparamagnetic and ferrimagnetic nature of nano-size particles and the change of hyperfine parameters. The observed reduction of a, values compared to bulk is due to the presence; of superparamagnetic fraction, size and surface effects for nano-size particles. Interestingly, a maximum H(ic) of 484.6 kAm(-1) and 448.8 kAm(-1) are achieved for nano-size BaFe(12)O(19) particles for Fe/Ba ratio of 10.8 and 12.0 respectively. These are the highest values reported for isotropic BaFe(12)O(19), which are close to the theoretical limit and explained based on coherent rotational model for an assembly of single domain particles oriented at random. The temperature dependence magnetization behaviour of nanosize BaFe(12)O(19) particles shows an enhancement of T(c) from 743 to 880 K when the particle size is reduced from 18.5 to 5.4 nm respectively and is explained using finite size scaling with correlation length upsilon = 0.67+/-0.06.