Magnetic properties of hydrothermally synthesized strontium hexaferrite as a function of synthesis conditions

Fine particles of strontium hexaferrite, SrFe₁₂O₁₉, with a narrow size distribution have been synthesized hydrothermally from mixed aqueous solutions of iron and strontium nitrates under different synthesis conditions. The relationship between the synthesis variables (temperature, time and alkali molar ratio) and the magnetic properties has been investigated. The results have shown that, as the synthesis temperature increases, the saturation magnetization of the particles increases up to a plateau and the coercivity decreases. As the alkali molar ratio R(=OH^–/NO ₃ ^– ) increases, the coercivity decreases and goes through a local minimum, while the saturation magnetization increases and goes through a local maximum. Increasing the synthesis time from 2 h to 5 h has no significant effect on the saturation magnetization, but decreases the coercivity. An anisotropic sintered magnet with a high saturation magnetization value of 67.26 e.m.u g^–1 (4320 G) has been fabricated from the hydrothermally synthesized powders.Relationship between the c.g.s and S.I.units which are used in this paper are as follows: 1 erg = 10^–7 J, 1 e.m.u. cm^–3 = 12.57×10^–7 Wom^–2 (tesla), 1 oersted (Oe) = 79.6 A m^–1, 1 G = 10^–4 tesla (T).