G. Mendoza-Suárez

Magnetic properties and microstructure of Ba-ferrite powders prepared by ball milling

Abstract The magnetic properties and the phase constitution of barium ferrite powders with Fe/Ba ratios varying from 7 to 15 and heat-treated in the temperature range 1000–1200°C are reported. The results showed that heating temperature was effective in increasing the magnetization ( M s ) of the powders for ratios ⩾10. For lower ratios M s increased initially and then decreased with increasing temperature, presumably due to the formation of BaFe 2 O 4 . The coercivity ( H ci ) presented a maximum for all the compositions and then decreased due to particle growth. In addition, the effect of the milling time on the magnetic properties and powder characteristics was investigated. It was found that 40xa0h of milling led to having samples with less volume fraction of second phases and that the magnetic properties were also maximized. TEM micrographs show particle sizes varying from 0.1 to 2xa0μm.

Preparation and magnetic properties of Ir-Co and La-Zn substituted barium ferrite powders obtained by sol-gel

Abstract The room temperature magnetic properties and microstructural characteristics of Ir–Co and La–Zn substituted Ba-ferrites powders prepared for the sol–gel method were investigated. Saturation magnetisation increased with La–Zn substitution in contrast to Ir–Co substitution. La–Zn mixtures were the least effective in reducing coercivity, whilst Ir–Co led to a fast reduction at low levels of substitution.

Influence of stoichiometry and heat treatment conditions on the magnetic properties and phase constitution of Ba-ferrite powders prepared by sol–gel

Abstract The magnetic properties and the microstructure of Ba-ferrite powders prepared by the sol–gel route were investigated. Amorphous gels were processed with a varying Fe/Ba ratio and then powder materials were obtained by heat treating at temperatures between 900 and 1000xa0°C for 1–4xa0h. The results showed that increasing time and temperature was beneficial to the saturation magnetisation (Ms), whereas the coercivity (Hci) was only slightly affected. The variation of the Fe/Ba ratio led to the formation of different proportions of BaFe12O19 and BaFe2O4, which directly affected the magnetic properties. Transmission electron microscopy (TEM) micrographs showed mainly hexagonal-like grains with crystallite sizes ranging from ∼50 to 150xa0nm.

Magnetic properties of Zn-Sn-substituted Ba-ferrite powders prepared by ball milling

Abstract The present investigation reports the preparation of BaFe 12−2x Zn x Sn x O 19 ferrite powders via ball milling and subsequent heat treatment. Starting powders were milled during 50 and 100 h, and then heat treated at 950 and 1000°C to induce crystallization and reaction of the starting materials. XRD results showed that it is possible to obtain single-phase barium ferrite powders if processing conditions are carefully chosen. The powders were also characterized for magnetic properties, namely saturation magnetization and intrinsic coercivity. It was found that coercivity could easily be controlled by varying the dopants content, while maintaining a relatively high magnetisation.

Magnetic properties of BaFe11.6–2xCoxTixO19 particles produced by sol–gel and spray-drying

Abstract Ba-ferrite powders of composition BaFe 11.6−2 x Co x Ti x O 19 (with x varying from 0 to 1.1) were prepared by the sol–gel and spray-drying techniques. Green powders showed an amorphous structure. They were heat-treated from 850°C to 1000°C to promote crystallisation and to study the dependence of the magnetic properties on the annealing temperature. Unlike the evaporation-dried powders, the spray-dried samples showed a highly homogeneous structure, which consisted of spherical particles with sizes ranging from 0.1 to ∼0.3xa0μm. As for the magnetic properties, the saturation magnetisation and remanence remained practically constant up to x =0.8 for all heating temperatures, whereas the coercivity fell uniformly as x increased from ∼5.5 to ∼0.1xa0kOe.

Effect of roll speed on the magnetic properties of nanocomposite PrFeB magnets prepared by melt-spinning

Abstract Rapid solidified Pr x Fe 94− x B 6 alloys, with x ranging from 6 to 10 at%, were prepared by melt-spinning at several roll speeds to obtain nanocomposite PrFeB magnets with enhanced properties. Magnetic properties and grain-size measurements were performed on as-cast ribbons and were correlated to roll speed. It was found that the greatest J r enhancement occurred at roll speeds that led to grain sizes below ∼30xa0nm. Deviations from this optimum value, caused either by partial amorphisation or grain coarsening, greatly affected the values of J r , j H c and ( BH ) max .