Mechanosynthesis of Gd0.3Sr0.7Fe12O19: crystal structure and magnetic properties

Abstract

In this work, results of the use of high-energy milling to produce gadolinium-doped strontium hexaferrite, Gd0.3Sr0.7Fe12O19, are presented. The objective of this work was to study the relationship between the synthesis conditions of hexaferrite powders, the crystalline structure and its magnetic properties (saturation magnetization and coercivity). Stoichiometric mixtures of Gd2O3, SrCO3 and Fe2O3 powders were subjected to grinding for 5 h, in a SPEX 8000D mill in an air atmosphere, using a ball:powder weight ratio of 10:1. The ground powders were subjected to heat treatment for 2 h at temperatures between 500 and 1200°C. RX diffraction was used to elucidate the crystal structure as a function of heat treatment temperature. Magnetic properties were determined using a vibrating sample magnetometer (MMV). The results showed that it is feasible to obtain Gd0.3Sr0.7Fe12O19 with a hexagonal structure by means of mechanosynthesis and subsequent heat treatment at a temperature above 800°C, with the presence of hematite, Fe2O3, which has not reacted completely. Temperature increases in the treatment do not modify the crystalline structure, it only decreases the amount of hematite present and therefore, the magnetic properties. The synthesized powders presented high coercivity (7.7 kOe) and adequate saturation magnetization, 43.7 emu/g, at 18 kOe, a little lower than that reported due to the presence of small proportions of hematite.