Anomalous magnetic response of the valence-fluctuating compound YbInCu4
  The exact solution of the spin one-half Falicov-Kimball model, with random hopping between the lattice sites, is used to explain the anomalous magnetic response of Yb-based valence-fluctuating intermetallic compounds. The anomalous behavior arises from an entropy-driven local-moment--nonmagnetic transition of unhybridized Yb ions in these materials which can also be used to explain the observed metamagnetism and resistivity anomalies. 
J. K. Freericks (Georgetown University) and V. Zlatic (Georgetown   University and Institute of Physics, Zagreb University)