The magnetization of Pb1-xCexS single crystals was measured at 20mY, and ma
gnetic field up to 90 kOe. Magnetization steps from two types of pairs were
observed. The first has an isotropic exchange interaction with J = -0.32 K
. The second type of pairs gives a structured step which can be explained b
y an anisotropic exchange interaction. Cluster statistics suggests that bot
h types are nearest-neighbor pairs. (C) 2001 Elsevier Science B.V. All righ
ts reserved.