Pressure-induced magnetic ordering in KCuCl3

KCuCl3 is a singlet ground state system with excitation gap Delta of 31K. The magnetization measurements under applied hydrostatic pressure show the existence of the magnetic order above the critical pressure Pc=8.8kbar. We report here on the first neutron diffraction observation of the pressure-induced antiferromagnetic ordering in KCuCl3 under hydrostatic pressure of 11kbar. The magnetic structure will be discussed and compared with the pressure-induced magnetic order observed in TlCuCl3, an isostructural three dimensionally coupled dimer system.