Field-induced magnetic ordering in the quantum spin system KCuCl3 -: art. no. 104405

KCuCl3 is a three-dimensional coupled spin-dimer system and has a singlet ground state with an excitation gap Delta/k(B)=31 K. High-field magnetization measurements for KCuCl3 have been performed in static magnetic fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire magnetization curve including the saturation region was obtained at T=1.3 K. From the analysis of the magnetization curve, it was found that the exchange parameters determined from the dispersion relations of the magnetic excitations should be reduced, which suggests the importance of the renormalization effect in the magnetic excitations. The field-induced magnetic ordering accompanied by the cusplike minimum of the magnetization was observed, as in the isomorphous compound TlCuCl3. The phase boundary was almost independent of the field direction, and is represented by the power law. These results are consistent with the magnon Bose-Einstein condensation picture for field-induced magnetic ordering.