A small magnetization jump at B-c = 12.5 T in CsCuCl3 found in 1978 ha
s been a mystery for a long time. In this compound, the magnetization
was supposed to be linear because of smooth tilt of the magnetic momen
ts toward the field direction for B parallel to c-axis. Then a jump wa
s completely unexpected by the molecular field model. Recently, Shiba
proposed a model where the 120 degrees-structure at low field changes
to the coplanar type above B, due to a quantum effect. This is the fir
st example which shows a quantum effect in high fields very dearly in
a magnetic system with strong frustration. This structure is confirmed
by high field neutron diffraction and high held submillimeter wave ES
R. But the plateau observed in the magnetization for B perpendicular t
o c is still an open question.