| Hexagonal ferrites such as strontium ferrite and barium ferrite [Sr(Ba)Fe12O(19)] have been intensively investigated during the last few decades due to its considerable importance to the electronic material industry. It can be used for many applications such as traditional permanent magnets, high-density magnetic and magneto-optic recording media, and microwave filters. In M-type hexaferrites, the iron ions occur on five different sites: the octahedral sites, crystallographically known as 2a, 12k and 4f2, and the tetrahedral sites 4f1 and 2b. In the magnetically ordered state, the 12k, 2a and 2b sites have their spins aligned parallel to each other and to the crystallographic c-axis, whereas those of 4f1 and 4f2 point into the opposite direction. So the available hard magnetic materials have a lower saturation magnetization Ms. In order to improve magnetic properties of hexaferrites, many studies have been carried on. In this dissertation, La-Co substituted Sr1-xLaxFe12-xCoxO19, M-Type strontium ferrites were prepared by ceramic processing. The precursor with different composition was investigated to clarify the forming conditions of the ferrites. The crystal structure and magnetic properties was studied by means of X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and permanent-magnet material measuring instrument. The influences of the La-Co substituted strontium ferrites on structure and magnetic properties of Sr1-xLaxFe12-xCoxO19, were systematically investigated. The main results were as follows: 1 , The results of phase transition of Sr0.82La0.18Fe11.82Co0.18O19 indicated thatγ-Fe2O3 phase was formed below annealing temperature 500°C. antiferromagneticferrite SrFe2O4 can be observed at temperature 550°C, and magnetoplumbite phase (M phase) at temperature 650 °C . single-phase strontium ferrites with magnetoplumbite structure are obtained when temperature is beyond 850°C. 2, It is found that the suitable amount of La3+-Co2+ substitution may remarkably...
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