Partial phase transition and quantum effects in helimagnetic films under an applied magnetic field

TL;DR

This paper investigates phase transitions and quantum effects in helimagnetic films under an external magnetic field, revealing layer-specific behaviors and the influence of quantum fluctuations through Monte Carlo and Green's function methods.

Contribution

It introduces a detailed analysis of partial phase transitions in helimagnetic films under magnetic fields, combining Monte Carlo simulations and Green's function techniques to explore classical and quantum effects.

Findings

Partial phase transition involving specific layers.

Layer-dependent spin configurations under magnetic field.

Quantum fluctuations cause non-uniform zero-point spin contractions.

Abstract

We study the phase transition in a helimagnetic film with Heisenberg spins under an applied magnetic field in the c direction perpendicular to the film. The helical structure is due to the an-tiferromagnetic interaction between next-nearest neighbors in the c direction. Helimagnetic films in zero field are known to have a strong modification of the in-plane helical angle near the film surfaces. We show that spins react to a moderate applied magnetic field by creating a particular spin configuration along the c axis. With increasing temperature (T), using Monte Carlo simulations we show that the system undergoes a phase transition triggered by the destruction of the ordering of a number of layers. This partial phase transition is shown to be intimately related to the ground-state spin structure. We show why some layers undergo a phase transition while others do not. The Green's function method for non collinear magnets is also carried out to investigate effects of quantum fluctuations. Non-uniform zero-point spin contractions and a crossover of layer magnetizations at low T are shown and discussed.