Here is our Ebook chapter on AC effects - http://www.allaboutcircuits.com/vol_2/chpt_9/8.html.
The change from one state of magnetization to the other requires some work being done to shift all those domains' orientations. The equivalent loss could be simulated by a resistance of appropriate value.
Try this link to a reasonably lucid article - http://info.ee.surrey.ac.uk/Workshop/advice/coils/power_loss.html.
And an experiment to demonstrate the effect - http://info.ee.surrey.ac.uk/Workshop/advice/coils/BHCkt/index.html.