QUANTUM EFFECT IN THE HIGH-FIELD PHASE OF CSCUCL3

A small magnetization jump at B-c = 12.5 T in CsCuCl3 found in 1978 has been a mystery for a long time. In this compound, the magnetization was supposed to be linear because of smooth tilt of the magnetic moments toward the field direction for B parallel to c-axis. Then a jump was 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 first 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 ESR. But the plateau observed in the magnetization for B perpendicular to c is still an open question.