Analysis of wasp-waisted hysteresis loops in magnetic rocks
  The random-field Ising model of hysteresis is generalized to dilute magnets and solved on a Bethe lattice. Exact expressions for the major and minor hysteresis loops are obtained. In the strongly dilute limit the model provides a simple and useful understanding of the shapes of hysteresis loops in magnetic rock samples. 
R S Kharwanlang and Prabodh Shukla
cond-mat.dis-nn cond-mat.stat-mech