Abstract
It is shown that the zeros of the partition function of the anisotropic Heisenberg ferromagnet locate on the unit circle in the complex "fugacity" plane, and all the spin correlation functions are non-negative when no external magnetic field is present.
- Received 29 April 1970
DOI:https://doi.org/10.1103/PhysRevLett.24.1409
©1970 American Physical Society
