EXPLICIT RESULTS FOR THE CORRELATION LENGTH OF THE FINITE-SIZED SPHERICAL MODEL OF FERROMAGNETISM

We report explicit results for the zero-field correlation length, xi(T; L), of a spherical-model ferromagnet confined to geometry L(d-d') x infinity(d') (d > 2, d' less-than-or-equal-to 2) and subjected to 'twisted' boundary conditions. In the region of first-order phase transition ( T< T(c)), xi under 'twisted' boundary conditions obeys the same scaling law as under periodic boundary conditions, though with a different amplitude. In the 'core' region (T congruent-to T(c)), the scaling behaviour changes radically as one moves from one set of boundary conditions to the other affected greatly by the 'pinning' of the ground-state wavevector k0 of the system.