AC susceptibility of thin Pb films in intermediate and mixed state

► Thickness dependent transition in AC susceptibility between intermediate and mixed state in type-I superconducting films. ► The temperature induced crossover between reversible and irreversible behavior was observed in the thicker film. ► The temperature dependence of the AC susceptibility in mixed state follows prediction of model based on Bean critical state. ► The temperature dependence of the harmonics of the complex AC susceptibility in the intermediate state is explained.