Effects of composition and temperature on the magnetic properties of (Ba,Sr)3Co2Fe24O41 Z type hexaferrites

The magnetic properties of Sr3-xBaxCo2Fe24O41 (0 ≤ x ≤ 3) Z-type hexaferrite powders have been investigated from 5 to 390 K. Results show that the lattice parameters (a and c) of the hexaferrite change with the Ba2+/Sr2+ ratio but don't follow the Vegard's law. The magnetization reversal process changes from three-stage reversal process to two-stage reversal process as the Ba2+/Sr2+ ratio increases. The above composition dependent magnetization reversal process of Sr3-xBaxCo2Fe24O41 can be explained with the composition dependent conical magnetic structure model. The saturation magnetization of Sr3-xBaxCo2Fe24O41 decreases only slightly with increasing the Ba content, but rapidly with increasing temperature. The coercivity (Hc) decreases with increasing temperature generally. Increasing Ba2+/Sr2+ ratio leads to an increase in Hc firstly and then Hc decreases again at temperatures below 250 K. An increase in temperature does not lead to enormous changes of the magnetization in the field cooling curves below 390 K, but leads to a successive increase of the magnetization in the zero field cooling curves generally.