Anomalous effects in minor hysteresis loops

We have studied minor hysteresis loops in thin films and measured time dependence at points around the minor loops. We find a linear dependence of the magnetic viscosity S(=dM/dln(t)) with field. We also observe a change in S from negative (decreasing M) to positive (increasing M) values whilst the applied field is still negative. From these results we infer that time dependent changes in the irreversible component of magnetisation, driven by local interaction fields, are at least partially responsible for the minor loop anomaly. In this paper we therefore describe the effect of the nature and scale of the coupling on the anomaly in the minor loops. We find that the minor loop area is enlarged for predominantly dipolar coupled materials.