Spin excitations in the two-leg ladder antiferromagnet CaV2O5

The nuclear spin-lattice relaxation rate (1/T-1) at the V sites in CaV2O5 w as measured. The relaxation rate in tile two-leg ladder was calculated with a strong-coupling expansion (J(perpendicular to) much greater than J(paral lel to)). and the result was compared with the experimental data. The compa rison of the temperature dependence shows a good agreement and provides an estimate of both J(perpendicular to) and J(parallel to) as well as the ener gy gap Delta. The magnetic field dependence of 1/T-1 is also reproduced wit h this approximation in the temperature range T less than or similar to Del ta /4. It is found that the magnon-magnon collision, which leads to a diffu sive behavior, is negligible in this temperature range. The effect of inter -ladder coupling is investigated and found to be weak in CaV2O5. Thus the s trong-coupling expansion calculation a grees satisfactorily with tile exper imental data, but a discrepancy between the exchange parameters deduced fro m the magnetic susceptibility and 1/T-1 is found.