Quantum Monte Carlo simulation of thin magnetic films

Abstract

The stochastic series expansion quantum Monte Carlo method is used to study thin ferromagnetic films, described by a Heisenberg model including local anisotropies. The magnetization curve is calculated, and the results compared to Schwinger boson and many-body Green's function calculations. A transverse field is introduced in order to study the reorientation effect, in which the magnetization changes from out-of-plane to in-plane. Since the approximate theoretical approaches above differ significantly from each other, and the Monte Carlo method is free of systematic errors, the calculation provides an unbiased check of the approximate treatments. By studying quantum spin models with local anisotropies, varying spin size, and a transverse field, we also demonstrate the general applicability of the recent cluster-loop formulation of the stochastic series expansion quantum Monte Carlo method.Comment: 9 pages, 12 figure

Directed loop updates for quantum lattice models

“…One can then terminate the path if there was only one link-discontinuity present before this step. This can be achieved by requiring no linkdiscontinuity at the initial entrance leg [9]. This starting condition is not possible when there is a conservation law as no new configuration would result, but in the absence of a conservation law, state changes on the exit leg can occur even if there is no state changes on the entrance leg.…”

Anisotropic susceptibilities of thin ferromagnetic films within many-body Green function theory: single-ion anisotropy versus exchange anisotropy

“…[3] and [5] and we do in the present paper, an approximate decoupling on the level of the lowest-order Green's functions proposed by Anderson and Callen [6], which however is only a good approximation for small anisotropies, as we showed in Ref. [7] by comparing with 'exact' Quantum Monte Carlo calculations. In keeping with Refs.…”

Hybrid quantum-classical Monte Carlo study of a molecule-based magnet

“…Quantum MC methods have been previously applied to high-spin models and here we follow the method described in Ref. [13]. As explained below, that method has been modified to treat the Ising-like orbital angular momentum.…”