Li and Ba ferrite nanoparticles prepared by self combustion

Abstract

The microstructure evolution during the heat treatments of Ba and Li ferrite powders prepared by self combustion is reported in terms of the effect of treatment time on densification, grain growth and some magnetic properties. The optimum size of the Ba ferrite crystallites was obtained by thermal annealing at 1000 °C for 10 min. The coercivity H c increases with increasing the annealing time and attains a maximum value of 4900 Oe which is much larger than that obtained by using a conventional method for the preparation of Ba hexaferrite. Li ferrite prepared by self combustion is characterized by low density and high electrical resistivity. O having a 10% metal concentration were prepared. Separately, an aqueous solution with 10 % polyvinyl alcohol concentration was prepared. Then, equal parts of the two solutions were mixed and a homogeneous solution with 5% metals and 5% colloid was obtained. Then, a small amount of ammonium hydroxide was added to the solution to adjust the pH value (pH ~ 8). The precipitation of metal hydroxides into the colloidal medium takes place according to the reaction LiNO 3 + 5Fe (NO 3 ) 3 + 16NH 4 OH → LiOH + 5Fe (OH) 3 + 16NH 4 (NO 3 ).(1) By a quick combustion, hydroxides convert to oxides and ferrite synthesis begins by the reaction LiOH + 5Fe (OH) 3 → LiFe 5 O 8 + 8H 2 O .(2) The ferrite powder is composed of submicron particles and small values of magnetic parameters. The resulting powders after combustion were heated at 500 °C for 30 minutes and then pressed in a disc and toroid shape in a stainless steel die under a pressure of about 3 · 10 7 N/m 2 . The pellets (17 mm diameter, 2-3 mm thick) and toroids (18 mm exterior diameter, 13 mm interior diameter, 3-4 mm thick) were heat treated in air at 1000 °C for 10, 20, 40 and 80 minutes to realize densification. The sintered ceramics were analyzed using X-ray diffraction to evidence the structure. After each thermal treatment the volume shrinkage, saturation magnetization, remanence magnetization and electrical resistivity were measured. The green pressed samples exhibit high porosity. By sintering at 1000 °C a strong volume shrinkage of specimens was noticed, which depends on the sintering time. From Fig. 1 one can observe that the volume significantly decreases after 20 minutes of the thermal treatment. By increasing the treatment time,

The influence of Nd–Co substitution on the magnetic properties of non-stoichiometric strontium hexaferrite nanoparticles

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“…Different routes have been tried to prepare nanosized singledomain particles [5][6][7][8]. In most cases, the attempt to get singlephase materials failed when the heat-treatment temperature remained below 1200 1C, giving large multi-domain particles not suitable for recording applications.…”

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