The Study Of Structure And Magnetic Properties Of Ions Substituted M-type Nano Barium Ferrite Materials

Owning to the high single-axis magnetocrystalline anisotropy, residual magnetization and magnetic energy product, M-type hexagonal ferrite (BaM, SrM) has been as a kind of important functional magnetic material used in every area. Because the magnetic properties are still lower than the theoretical values in M-type barrium, many studies have been done to improve the magnetic properties. The research discovered that the magnetic properties could be improved in certain extent by optimizing preparation conditions including Fe3+/Ba2+ mole ratio, sitering temperature and time and pH value of solution. For all this, the magnetic properties cannot reach to the theoretical values. A new method, ions substituted method, has been developed and has become the research hot spot. It's key to improve the magnetic properties, incling the coercive force HC, saturation magnetization MS, residual magnetization Mr and magnetic energy product (BH)max, by ions doped method.There are many preparation methods to synthesis M-type barium. The samples were prepared by sol-gel method in our research. The optimized prepared conditions had been obtained:Fe3+/Ba2+ mole ratio is 12, sitering temperature is 900?, sitering time is 3 h and pH value is 7. The ions substituted samples BaxRe1-xMexFe12-xO19 (Re: rare earth ions, Me:transitional metal ions and x:doped content) were prepared by sol-gel method under the above optimized preparation condition. X-ray diffractometer (XRD) and vibration sample magnetometer (VSM) were used to research the crystal structure and magnetic properties respectively. The radii of rare earth ions are similar to that of Ba2+ and therefore can substitute Ba2+. In addition, rare earth ions with high magnetocrystalline anisotropy determind by spin-orbital coupling can enlarge the coercive force HC which is associated to magnetocrystalline anisotropy. For rare earth ions, the magnetic electrons which "live" deeply in the atom can hardly been influenced by the outside crystal field which can make the orbital angular momentum quenched. The radii of thentransitional metal ions are simiar to that of Fe3+ and therefore can substitute Fe3+. The transitional metal ions with lower magnetocrystalline anisotropy were easily influenced by the crystal field which makes the orbital angular momentum quenched. The transitional metal ions substituted Fe3+ at different crystal lattice can change the saturation magnetization MS.Three series ions-substituted samples were synthesized by sol-gel method. The first two series are Sm3+(Sm3+-?Sm3+Zn2+-?Sm3+Co2+- and Sm3+Co2+Zn2+-doped) and Gd3+(Gd3+-?Gd3+Zn2+-?Gd3+ Mn2+-?Gd3+ Zn2+Mn2+-doped) series, named by rare earth ions. Sm3+(L=5, S=5/2) and Gd3+(S=7/2.L=0 causing magnetocrystalline anisotropy zero) are selected to discuss the spin-orbital coupling effect on the HC. The transitional metal ions Zn2+ (nonmagnetic), Co2+ (3.7?B) and Mn2+ (5.0?B) are selected to substitute Fe3+. By comparing the magnetic properties, which sites the substituted ions can be found.Finally, in order to study systematically the influence of rare earth ions on the magnetic properties, seven rare earth ions were selected to prpepare ions-doped samples. The saturation magnetization Ms decreases with the shrinkage of rare earth ions and the coercive force HC enhance with the increase of orbital quantum numbers.