Transverse susceptibility and magnetic anisotropy of CoTi-doped barium hexaferrite single crystals

Abstract

Measurements of the reversible transverse susceptibility (RTS) were performed on BaFe12−x−yCoxTiyO19 single crystals with doping concentrations x≊y≤0.77 under different angles ϑ0 between the easy axis and applied field. For intermediate doping concentrations the occurrence of a peak in the RTS curve for ϑ0=90° indicates that the domain walls are not free to move. This assumption is confirmed further by the large component of the RTS being out of phase with respect to the excitation field HE. The phase angle of the initial susceptibility measured parallel to the easy axis becomes maximum at a characteristic excitation field value HE,C and a relaxation of the susceptibility is observed if HE steps from zero to a value larger than HE,C. Using the RTS curve for ϑ0=0 and assuming 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 HA=2K1/(μ0Ms) and the second-order anisotropy constant K2 can be determined. The values found this way are compared to results from magnetization-curve analysis and from other authors.