Historical dip effect

Based on bulk flux pinning framework, we have observed numerically the history effect in the ac susceptibility χ( T) (acs). Our calculation meets well the behavior of χ in 2H–NbSe 2, showing the bulk model works well. In addition, the numerical result shows that a peak in critical current density, which is usually accompanied by vortex melting transition, may not be observed as a dip in acs, which is a dynamic response of a sample to the applied ac field and dependent on ac field frequency and amplitude.