Magnetic Properties of Magnetically Soft Nanocomposite Co–SiO₂ Prepared via Mechanical Milling

Abstract

Nanocomposite of Co-SiO2, a soft magnetic material, with Co weight fraction x = 0.3 and 0.7 was prepared via mechanical milling. The magnetic properties of these samples, both zero-field-cooled (ZFC) and field-cooled (FC), have been measured as a function of x, milling time, and temperature. The structural assessment of the composite indicates a presence of only ferromagnetic (FM) hcp-Co phase in the composite. However, reported magnetic properties of these composites appear to be dependent on the presence of antiferromagnetic (AFM) phases of cobalt oxide as well. The observed enhancement in ZFC coercivity and a reduction in saturation magnetization with the milling time are due to an increase in defect density upon milling. The ZFC coercivity for the x = 0.3 samples has been found to be much higher than the x = 0.7 samples for all milling times. The coercivity above 50 K depends on temperature according to the law corresponding to isotropic uniaxial superparamagnetic particles. Below 50 K the presence of an AFM phase Co3O4 (TN approximately 33 K) and increased interparticle interactions bring in a departure from that law. The saturation magnetization is found to be temperature dependent for the x = 0.3 samples and temperature independent for the x = 0.7 samples, which further provides evidence of the presence of higher AFM phase fraction in the composite with a low metal volume fraction. The FC magnetic measurements show a presence of an exchange bias field and an enhanced coercivity which are higher than the ZFC measurements. All magnetic measurements indicate that the overall magnetic properties of the composite are dictated by the presence of a trace amount of cobalt oxides.

Microstructure and Magnetic Properties of Nano-Sized Ba-Al Ferrite Particles by High Energy Ball Milling

“…It has been generally accepted that a nano-composite magnet with a mixture of hard and soft magnetic phase can be a good candidate for rare earth hard magnet. 1 The BaAl 2 Fe 10 O 19 that is one of new hard magnet without rare earth elements has been attracted much attention because of its high uniaxial magnetic anisotropy, high curie temperature, large saturation magnetization, high coercive force, excellent chemical stability, high corrosion resistivity and low cost. 2 High energy ball milling is a process of mechanical alloying (MA) that starts with the powder along with the grinding medium (STS balls), then mills for the desired length of time at very high speed.…”

Toxicogenomics to Improve Comprehension of the Mechanisms Underlying Responses of In Vitro and In Vivo Systems to Nanomaterials: A Review

“…There are indications in the literature that manufactured nanoscale materials may spread in the body in unpredictable ways, and certain nanoscale materials have been observed to preferentially accumulate in particular organelles. Furthermore, the unique and diverse physicochemical properties of nanoscale materials suggest that their toxicological properties may differ from those of the corresponding bulk materials [ 9 ].…”