Investigation of Formation Mechanism, Magnetic Properties and Micro Structure of Calcium Hexaferrite

In this research، calcium hexaferrite with nominal composition (Ca1-XLaXFe12O19)، (X=0. 0، 0. 2، 0. 4 and 0. 6) and Fe3+/Ca2+ mole ratio=11 have been synthesized through the co-precipitation route. The ferrite precursors were obtained from aqueous mixtures of calcium nitrate، ferric nitrate and lanthanum nitrate by precipitating calcium، iron and lanthanum ions using 2M sodium hydroxide solution at pH=14 and room temperature. These precursors were calcined at 1200 ◦C for constant calcination time 1 h in a static air atmosphere. Several methods such as X-ray diffraction (XRD)، scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) have been used to obtain detailed information on the crystallography، formation mechanism، morphology and magnetic properties of the powders with different amounts of La. The X-ray diffraction pattern of the powders with La indicates the formation of calcium hexaferrite and also α-Fe2O3 was detected beside the M-phase. However in powders without any amount of dopant، CaFe4O7 and α-Fe2O3 phases were formed. The results of SEM showed that the CaM grains were hexagonal platelets with sizes from 1 to 2 µm. VSM measurement also indicated that maximum magnetization (MMax) and coercivity (Hc) of the calcined powders increased by using of La. Low values of coercive field (200 Oe) and of the maximum magnetization (50 emu. g-1) were obtained on powders