Effect of quantum fluctuations on magnetic ordering in CaV3O7

We present a theoretical model for CaV3O7: the 1/4-depleted square spin-1/2 Heisenberg model which includes both the nearest-neighbor coupling (J) and the next-nearest-neighbor coupling (J'), where J and J' are antiferromagnetic. Recent investigations on neutron diffraction by Harashina et al. revealed the occurrence of magnetic ordering at low temperatures, which may be called a stripe phase. It is shown that the observed spin structure is not stable according to the classical theory. By employing the modified spin wave theory we show that the stripe phase is stabilized by the quantum fluctuations for J'/J > 0.69. In CaV3O7, J and J' are estimated to be nearly equal throughout comparison of the theoretical and experimental results.