Effect of RE ion valency variation in Tb and Dy doped magnetic SrFe10−xRExO19 hexaferrite

M-type hexaferrites are focused of much research because of its outstanding properties such as high saturation magnetism (Ms), high coercivity (Hc), high permeability and low conductive looses, excellent chemical stability, and corrosion resistivity. Because of these properties M-type ferrite find wide industrial applications ranging from microwave devices to recording media [1]. The magnetic and electric properties of these ferrites can be tuned by replacing Fe³⁺ or Sr²⁺/Ba²⁺ with magnetic or non-magnetic ion. The result of these substitutions is to alter magnetocrystalline anisotropy and magnetization to suite particular application. Recent reports have shown the effect of high concentration of RE³⁺ doping in the M-type of ferrite [2, 3, 4, 5]. The work by Wang [5], the magnetism reduced from 64 emu/g to 64 emu/g with doping of lanthanum (La) with x=0.25at 1200°C while the coercivity was increased greatly from 1.95 kOe to 3.4 kOe. Karimi´s group [6] showed that the small amount of Ce doping in ferrite leads to variation in the lattice parameter due to dual valence Ce^3+/4+. In the present study we have synthesized SrRE_xFe_12-xO₁₉ (RE=Tb or Dy) where RE ions are known display multivalence. Consequently it is important to understand the concomitant structural and magnetic changes resulting from variation in RE valency. The valency changes in turn changes their ionic radii and anisotropy.