Field-induced staggered magnetization near impurities in the S= one-dimensional Heisenberg antiferromagne

We report an impurity effect in the spin- one-dimensional Heisenberg antiferromagnet (Formula presented)(Formula presented). The (Formula presented) NMR spectra develop a broad background with sharp edges at low temperatures. The anisotropy and the temperature dependence of this structure indicate that the external magnetic field induces local staggered magnetization near impurities, whose spatial extent grows with decreasing temperature. The results are in good agreement with the theoretical prediction by Eggert and Affleck for a semi-infinite spin chain with an open end. © 1997 The American Physical Society.