| M-type strontium hexaferrites has been widely applied in the field of high density magnetic recording media, DC electric machine, high frequency electromagnetic devices, microwave[1-4] etc. because of a series of advantages such as its cheap raw materials, excellent resistance to oxidation, higher coercivity, energy product and the uniaxial magnetic anisotropy and so on. In order to meet the realistic needs, a large number of research committed to use kinds of means to improve the performance of strontium ferrite such as doping[5], hot pressing[6], ionic replacement[7] and the other method.According the principle of the valence state of balance and the similar ionic radius replacement, It has been reported that partial substitutions of La3+and/or La3+-Co2+into strontium ferrites improve significantly the magnetic properties[8-11], but the previous work focused on strontium ferrite magnetic properties, and microwave absorption properties and so on, little research on the magneto-optical Kerr effect. Since the magnetic rotation effect was found for the first time in1845, the magneto-optical effect has not been a wide range of applications. Until recent years, with depth study of the magneto-optical effect, magneto-optical Kerr effect on information storage and sensor applications[12-14] has gradually become one of the hot studies.Strontium ferrites Sr1-xLaxFe12O19(x=0,0.05,0.10,0.15,0.20) and Sr0.85-xLaxCa0.15Fe10.6Co0.4O19(x=0.45,0.50,0.55,0.60,0.65) were prepared by the conventional high-temperature solid phase reaction. The process consists of several steps as follows:raw material analysis weighing, milling, drying, pre-pressing, pre-sintering, milling, pressing, sintering. The X-ray diffractometer, vibrating sample magnetometer were used to characterization of the structure of the samples and scanning electron microscope and magneto-optical ellipsometer were used to characterize the properties of the samples. The influence of the amount of substituted La and La/Co on the structure, morphology, optical, magnetic properties and transverse magneto-optical Kerr effect of the samples were studied. The results obtained as follows:1. Improve the sintering temperature within a certain range, appropriate to extend the holding time can eliminate the materials impure phase effectively. In our experiment, the lower coercivity of strontium ferrite should be needed, we obtained the optimum sintering temperature that can reduce the coercivity effectively through several experiments. At last, the coercivity was lower enough to help detecting the magneto-optical Kerr activity with the in-plane applied field used in this work (for the test range is-240kA.m-1-240kA.m-1).2. Lattice constants a and c will have different changes in the strontium ferrite for doped, the lattice constant c will be decrease with the doping amount of La increases, but the lattice constant a will changed a little. Whether lanthanum or lanthanum-cobalt mixed doped, specific saturation magnetization and coercive force of the strontium ferrite will be changed. In this study, we found the Strontium ferrites have the same trend in different experiments. With the increase of La doping amount, the specific saturation magnetization and coercive force are all become higher.But the undoped samples exhibits a high coercivity.3. There are magneto-optical kerr effect in the La-doped and La-Co mixed doped strontium ferrites. For the M-type strontium ferrite has a strong uniaxial magnetic anisotropy, the magneto-crystalline anisotropy energy could be large, so the undoped M-type strontium ferrite almost no magneto-optical Kerr effect could be found. In this study, whether strontium-doped lanthanum or lanthanum cobalt mixed in the strontium ferrite, the magneto-optical Kerr effect have enhancement in varying degrees. For the minor crystallization of super-exchange interaction was influenced by the ions replacement. The magneto-optical activity became stronger with the La adoped, the magneto-optical activity of sample raises to almost0.4%-1%than SrFe12O19. |
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