Preparations And Magnetic Properties Of Substituted Barium Ferrite

M-type barium ferrite is magnetic functional material with wide potential applications. The investigation has focused on the new synthesis methods and modification on the characters in order to obtain good performance M-type barium ferrite. In this paper, M-type barium ferrite particles were synthesized via different methods, in which the better method was established to prepare the series doped samples. These materials were characterized by XRD, ESEM and VSM, and then studied in detail.Sol-gel method and co-precipitation technique are usual methods with many advantages. In this paper, BaFe₁₂O₁₉ particles were prepared by sol-gel, co-precipitation, coprecipitation-reflux methods, respectively. BaFe₁₂O₁₉ particles were obtained by calcining only at 700℃for co-precipitation technique, lower than the temperature used in Sol-gel method. Dispersible like-plate hexagonal BaFe₁₂O₁₉ particles were synthesized by coprecipitation-reflux method originating from modified co-precipitation technique. Using the method, the properties of the samples were affected on by the kinds of flux, different calcined time and temperature. When 100% KCl acted as reflux,BaFe₁₂O₁₉ particles were prepared by calcining at 450℃for 2hs and then at 950℃for 4hs in coprecipitation- reflux method. BaFe₁₂O₁₉ particles had 71.9 A·m²/kg of specific saturated magnetization (Ms) near the theoretical value, and 367.8kA/m of coercivity.Co²⁺, Zn²⁺, Mn²⁺, Sn⁴⁺ and La³⁺ doping M-type barium ferrite, BaFe_12-2xR_xSn_xO₁₉(R:Co²⁺, Zn²⁺, Mn²⁺) and Ba_1-xLa_xFe_12-xR_xO₁₉(R:Co²⁺,Mn²⁺) series samples were prepared by coprecipitation-reflux method. With increasing of substitution content x, lattice parameters increased, and particle sizes decreased. When R was Co²⁺, Zn²⁺ and Mn²⁺, respectively, coercivity and coercivitytemperature coefficient of BaFe_12-2xR_xSn_xO₁₉ decreased with increasing of substitution content x. On the other hand, Co²⁺ and Mn²⁺ doping contributed to improving Ms, while Zn²⁺ doping resulted in decreasing Ms at relative low x.Unfortunately, Ms and Coercivity of BaFe_12-2xZn_x/2Co_x/2Sn_xO₁₉ yet decreased with increasing of x so that BaFe_12-2xZn_x/2Co_x/2Sn_xO₁₉ was fail to be applied as the potential magnetic recording medium. For BaFe_12-2xMn_x/2Co_x/2Sn_xO₁₉ samples, Mswas higher than 72 A·m²/kg of theoretical value. The curve of Ms vs substitution content x had a crest at x=0.4, and Ms of BaFe_11.2Mn_0.2Co_0.2Sn_0.4O₁₉ was 78.4 A·m²/kg. When x was in the range from 0.5 to 0.6, M-type barium ferrite was potential high- density magnetic recording medium due to its high specific saturated magnetization, low temperature coefficient of coercivity and moderate coercivity from 80 to 240 kA·m^-1.For Ba_(1-x)La_xFe_(12-x)Mn_xO₁₉ and Ba_(1-x)La_xFe_(12-x)Co_xO₁₉,coercivities decreased with increasing of x.On the other hand, Ms of the former had little change, and Ms of the later firstly increased and then decreased. It could be concluded that La³⁺ dopant contributed to improving the coercivity of barium ferrite.