Please find this chapter

http://link.springer.com/chapter/10.1007%2F978-1-4899-2379-0_20

When you draw a M versus H magnetization curve, you get an hysteresis cycle as soon as your field is above Hc1, but it is not easy to detect,  and up to the so called irreversible field above which the magnetization stays on the same curve up to Hc2.

In this dc field range the alternating susceptibility  "Chi prime" is strongly diamagnetic, but there exists a "Chi second" component. Above the irreversibility field, "Chi prime" becomes positive, before to reach the susceptibility of the normal state "Chi normal"