Field-controlled phase separation at the impurity-induced magnetic   ordering in the spin-Peierls magnet CuGeO3
  The fraction of the paramagnetic phase surviving at the impurity-induced antiferromagnetic order transition of the doped spin-Peierls magnet Cu(1-x)Mg(x)GeO3 (x < 5%) is found to increase with an external magnetic field. This effect is qualitatively explained by the competition of Zeeman energy and exchange interaction between local antiferromagnetic clusters 
V. N. Glazkov, A. I. Smirnov, H.-A. Krug von Nidda, A. Loidl, K.   Uchinokura, T. Masuda