TRANSVERSE SUSCEPTIBILITY AND MAGNETIC-ANISOTROPY OF COTI-DOPED BARIUM HEXAFERRITE SINGLE-CRYSTALS

Measurements of the reversible transverse susceptibility (RTS) were pe rformed on BaFe12-x-yCoxTiyO19 single crystals with doping concentrati ons x approximate to y less than or equal to 0.77 under different angl es v(O) between the easy axis and applied field. For intermediate dopi ng concentrations the occurrence of a peak in the RTS curve for v(O)=9 0 degrees indicates that the domain walls are not free to move. This a ssumption is confirmed further by the large component of the RTS being out of phase with respect to the excitation field H-E. The phase angl e of the initial susceptibility measured parallel to the easy axis bec omes maximum at a characteristic excitation field value H-E,H-C and a relaxation of the susceptibility is observed if H-E steps from zero to a value larger than H-E,H-C. Using the RTS curve for v(O)=0 and assum ing that the peak of the RTS is located at the same field strength as if the particle were single domain, the first-order anisotropy field H -A=2K(1)/(mu(O)M(s)) and the second-order anisotropy constant K-2 can be determined. The values found this way are compared to results from magnetization-curve analysis and from other authors.