Magnetic resonances and magnetization in the spin ladder compound (VO)2P2O7

We present experimental results of magnetic susceptibility, magnetization and magnetic resonances on the S = 1/2 spin ladder system vanadyl pyrophospate [(VO)2P2O7]. In this system a spinware excitation gap of the order of EG = 50 K was observed with inelastic neutron scattering experiments at the boundary of the Brillouin zone. Our measurements were performed in powder samples in magnetic fields up to 14 T at temperatures down to 1.5 K and in the frequency range 55-345 GHz. We found a linear resonance branch corresponding to a g-factor g = 1.98. Strong evidence for chain end effects was observed in susceptibility and magnetization data as well as in the temperature dependence of the absorption line intensity. The lineshape of the observed resonances points to a slightly anisotropic g-tensor. In higher fields we resolve the single resonance branch into several distinguished absorption lines with different temperature dependences.