Effects of Y-Co co-substitution on the structural and magnetic properties of M-type strontium hexaferrites

Y3+- and Co2+-substituted Sr1-xYxFe12-xCoxO19 (0 < x < 0.50) M-type hexaferrites were synthesized using a traditional oxide ceramic process to study their structural and static magnetic properties. The well-defined Mtype phase structures of the pure and Y-Co co-substituted strontium ferrites were verified via XRD analysis. When the Y-Co substitution amount (x) exceeded 0.20, the Fe2O3, Y3Fe5O12, SrFe2O4, and CoFe2O4 impurity phases coexisted in the M-type strontium hexaferrite structure. The lattice parameters a and c increased when x < 0.20; however, a further increase in the Y-Co substitution caused them to decrease. The X-ray density dx initially decreased when x 0.20, and subsequently increased with a further increase in Y-Co substitution. The density of the sintered samples ds exhibited a decreasing trend with the increasing Y-Co substitution, inducing the porosity to increase. The saturation magnetization Ms monotonously decreased with the increasing Y-Co substitution amount. The in-plane and out-of-plane coercivities, Hc(ip) and Hc(op), initially increased as x increased from 0 to 0.20. When x 0.20, however, Hc(ip) exhibited a decreasing trend; particularly, a linear decrease was observed as x increased from 0.30 to 0.50. The squareness ratio S reached its maximum (79.6%) at x = 0.20.