Field dependence of RF susceptibility in the vicinity of a ferromagnetic transition in single crystals CeAgSb$_2$

A 10 MHz resonant technique was used to study ferromagnetic transition in single crystals CeAgSb$_2$. Detailed measurements of field and temperature dependencies of the dynamic susceptibility in the vicinity of the ordering temperature were performed. It was found that a sharp peak in zero-field response rapidly smears out in a weak ($\sim$100 Oe) magnetic field. Obtained results are compared to DC magnetic susceptibility and resistivity, - both showing no similar effect. The possible relation our measurements to study dynamics of a ferromagnetic transition is discussed.