Spontaneous magnetization of the XXZ Heisenberg spin-1/2 chain

Determinant representations of form factors are used to represent the spont aneous magnetization of the Heisenberg XXZ chain (Delta > 1) on the finite lattice as the ratio of two determinants. In the thermodynamic limit (the l attice of infinite length), the Baxter formula is reproduced in the framewo rk of Algebraic Bethe Ansatz. It is shown that the finite size corrections to the Baxter formula are exponentially small. (C) 1999 Elsevier Science B. V. All rights reserved.