Field Dependence of XY-Behavior in Frustrated S = 1/2 Square Lattices

T. Forster1,2, F.A. Garcia1,3, A. N. Ponomaryov2, R. Nath1,4, E.E. Kaul1, B. Schmidt1, S.A. Zvyagin2, C. Geibel1, J. Sichelschmidt1 1 Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany 2Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany 3 Instituto de Fisica ”Gleb Wataghin” , UNICAMP, Campinas-SP, 13083-970, Brazil 4 School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram-695016, India