Helimagnetic thin films: Surface reconstruction, surface spin-waves and magnetization

•Green's function method applied to non collinear helimagnetic films.•Ground-state spin configuration exactly determined.•Spin-wave spectrum and layer magnetizations calculated at finite temperatures.•Optical and acoustic surface-localized spin waves discovered.•Interesting quantum effects found for spin contractions and magnetization crossover.

Quantum properties of a helimagnetic thin film of simple cubic lattice with Heisenberg spin model are studied using Green's function method. We find that the spin configuration across the film is strongly non-uniform. Using the exactly determined spin configuration we calculate the spin-wave spectrum and the layer magnetizations as functions of temperature T. We show the existence of surface-localized modes which strongly affect the surface magnetization. We also show that quantum fluctuations cause interesting spin contractions at T=0 and give rise to a cross-over between layer magnetizations at low T.