Effective quantum pseudospin-1/2 model for Yb pyrochlore oxides
  An effective quantum pseudospin-1/2 Hamiltonian for Yb_2TM_2O_7 (TM = Ti and Sn) is obtained in terms of the atomic Kramers ground doublet of the LS coupling and the crystalline electric field, which is almost described with J^z=\pm 1/2. It is calculated microscopically as the sum of Anderson's superexchange interaction and the magnetic dipole interaction. It is found that it shows a strong exchange anisotropy. 
Shigeki Onoda
cond-mat.str-el cond-mat.stat-mech