Magnetic phase diagram and structure of the magnetic phases in the   quasi-one-dimensional antiferromagnet BaCu_2Si_2O_7: symmetry analysis
  We have performed a symmetry analysis of the properties of the recently discovered quasi-one-dimensional compound BaCu_2Si_2O_7. The existence of the unusual spin-reorientation transitions is explained as an effect of the unusually strong relativistic interactions. The possible connection between the magnitude of the relativistic interactions and the low-dimensional structure of the BaCu_2Si_2O_7 is discussed. The structure of the magnetic phases is determined. 
Vasiliy N. Glazkov, H.-A. Krug von Nidda