Double Magnetic Field-induced Phase Transitions in the Spin-1/2 Alternating Chain System AgVOAsO$_{4}$

The new spin-1/2 compound AgVOAsO4 shows one-dimensional magnetic behavior and a spin gap of about 14 K. The crystal structure of AgVOAsO4 is rather complex with alternating spin chains aligned along the [110] and [110] direction. The experimental magnetic susceptibility yields values of 40 K and 26 K for J1 and J1$'$, respectively. The magnetization curve taken at 1.5 K cannot be fully described by only two coupling constants, which points to sizable inter chain coupling. Furthermore, the magnetization shows the closing of the spin gap at Hc1 =10.5 T and a saturation at Hc2=48.5 T. In the talk, we report the magnetic field - temperature (H-T) phase diagram of AgVOAsO4 measured by specific heat and magnetization experiments. The specific heat taken in high DC fields up to 28 T reveals a distinct double anomaly around 4 K and 2 K. Magnetization experiments follow this double structure down to mk temperatures and reveal a variety of anomalies close to the critical field Hc1 in AgVOAsO4.