Spin Structure of S= 1/2 Quantum Spin System CaV ₃O ₇

The spin structure of magnetically ordered CaV3O7 has been determined by neutron powder diffraction. The structure is different from that expected within a simple classical Heisenberg model and therefore quantum effects seem to be significant in this system. By comparing the ordered moments of V4+ spins at two distinct sites with those derived using the modified spin wave theory [Kontani et al.: J. Phys. Soc. Jpn. 65 (1996) 1566.], information on the exchange coupling constants between V-spins can be obtained.