Effects of Frustrated Surface in Heisenberg Thin Films

TL;DR

This study investigates how frustrated surfaces affect the magnetic properties of Heisenberg thin films with triangular layers, revealing complex phase transitions and deviations from standard universality classes through Monte Carlo simulations and Green function analysis.

Contribution

It introduces a combined Monte Carlo and Green function approach to analyze frustrated surface effects in Heisenberg thin films, highlighting non-linear ground states and unique critical behavior.

Findings

Two phase transitions related to surface and interior layer disordering.

Good agreement between Monte Carlo and Green function results.

Deviation of critical exponent ratios from standard Ising universality classes.

Abstract

We study by extensive Monte Carlo (MC) simulations and analytical Green function (GF) method effects of frustrated surfaces on the properties of thin films made of stacked triangular layers of atoms bearing Heisenberg spins with an Ising-like interaction anisotropy. We suppose that the in-plane surface interaction $J_s$ can be antiferromagnetic or ferromagnetic while all other interactions are ferromagnetic. We show that the ground-state spin configuration is non linear when $J_s$ is lower than a critical value $J_s^c$. The film surfaces are then frustrated. In the frustrated case, there are two phase transitions related to disorderings of surface and interior layers. There is a good agreement between MC and GF results. In addition, we show from MC histogram calculation that the value of the ratio of critical exponents $\gamma/\nu$ of the observed transitions is deviated from the values of two and three Ising universality classes. The origin of this deviation is discussed with general physical arguments.