Spin excitations throughout the field-induced magnetic phase of the spin 1/2 alternating chain compound Cu(NO3)2.2.5D20

We present an inelastic neutron scattering study performed throughout the field-induced magnetic phase occurring between Hc1∼3.5T and Hc2∼4.5T in the spin 1/2 alternating antiferromagnetic chain compound Cu(NO3)2.2.5D20. The exchange couplings are consistently determined from the analysis of the spin dynamics both in the gapped phase, at H=0, and in the saturated phase, at H=6T, while the cancellation of the lowest energy gap in the complete field-induced magnetic phase suggests that this system is a good realization of a Bose-Einstein condensation