arXiv:cond-mat/0006448 · Physical review. B, Condensed matter
Surface scaling behavior of isotropic Heisenberg systems: Critical exponents, structure factor, and profiles
M. Krech
Abstract
The surface scaling behavior of classical isotropic Heisenberg magnets is investigated by Monte Carlo methods in $d=3$ dimensions for various values of the surface-to-bulk coupling ratio ${J}_{1}/J.$ For ${J}_{1}/J<~1.0,$ critical behavior according to the ordinary surface universality class is found. Estimates for magnetic surface exponents are presented and compared to older estimates and their theoretical counterparts. For ${J}_{1}/J>~2.0,$ scaling is still valid with effective exponents which depend on ${J}_{1}/J.$ The surface structure factor ${S}_{1}(p,L)$ is investigated at bulk criticality as a function of the momentum transfer p parallel to the surface and the system size L. For ${J}_{1}/J<~1.0$ and ${J}_{1}/J>~2.0$ the full p dependence of ${S}_{1}(p,L)$ can be captured by generalized shape functions to a remarkable accuracy. Profiles of the magnetization and the energy density also confirm scaling, where for ${J}_{1}/J<~1.0$ the ordinary surface universality class is recovered and for ${J}_{1}/J>~2.0,$ scaling with ${J}_{1}/J$ dependent exponents is found. For ${J}_{1}/J=1.5$ the system displays a striking crossover behavior from spurious long-range surface order to the ordinary surface universality class. For ${J}_{1}/J>~2.0$ the effective scaling laws must be interpreted as nonasymptotic and the value ${J}_{1}/J=1.5$ marks a crossover regime, in which the crossover from the nonasymptotic to the asymptotic (ordinary) surface scaling behavior can be resolved within numerically attainable system sizes.