Orientational and relaxation features of the dynamic magnetic susceptibility of PbFe$_{12}$O$_{19}$ upon transition from the magnetically ordered to paramagnetic state

The dynamic magnetic susceptibility of lead hexaferrite has been experimentally studied in the temperature range of the transition from the magnetically ordered to paramagnetic state. As the vector of the ac magnetic field is oriented in the easy-magnetization direction along hexagonal axis $c$, anomalous peakshaped decrease in the real part of the magnetic susceptibility has been observed near the Curie temperature. The observed effect depends on the ac magnetic field frequency and disappears at a frequency near 12 MHz. The observed features have been interpreted as the effects caused by the relaxation resonance.