Influence of a Magnetic Field on the Growth and Magnetic Properties of Zn_0.15Fe_2.85O₄ Nanoparticle Chains

Abstract

With the assistance of a magnetic field, H syn, a series of Zn0.15Fe2.85O4 (ZFO) nanoparticle chains (NCs) with a mean particle diameter of around ∼140 nm and different chain lengths are synthesized by mild oxidation of ferrous hydroxide gel. The Mössbauer spectra demonstrated that Zn ions were incorporated into the tetrahedral sites of the spinel structure. The remarkable influence of the increasing H syn on the growth of ZFO NCs is found not only in the increased length of the assembled particle chain but also in the improved crystallinity evidenced by the increased size of crystalline grains from 18 to 44 nm. The observed monotonous enhancement of saturation magnetization with increasing H syn is in perfect accordance with that of the relative absorption intensity ratio B/A determined by Mössbauer spectra, suggesting that the difference in the overall number of Fe ions between B and A sites is the main contribution to the magnetization owing to the weakening of the antiferromagnetic interaction among these two sites. Combined with ferromagnetic resonance, magnetic anisotropy of the grown ZFO NCs is found to strongly depend on the demagnetizing field associated with the elongated chain shape.