Quantum Theory of Helimagnetic Thin Films

Abstract

We study properties of a helimagnetic thin film with quantum Heisenberg spin model by using the Green's function method. Surface spin configuration is calculated by minimizing the spin interaction energy. It is shown that the angles between spins near the surface are strongly modified with respect to the bulk configuration. Taking into account this surface spin reconstruction, we calculate self-consistently the spin-wave spectrum and the layer magnetizations as functions of temperature up to the disordered phase. The spin-wave spectrum shows the existence of a surface-localized branch which causes a low surface magnetization. We show that quantum fluctuations give rise to a crossover between the surface magnetization and interior-layer magnetizations at low temperatures. We calculate the transition temperature and show that it depends strongly on the helical angle. Results are in agreement with existing experimental observations on the stability of helical structure in thin films and on the insensitivity of the transition temperature with the film thickness. We also study effects of various parameters such as surface exchange and anisotropy interactions. Monte Carlo simulations for the classical spin model are also carried out for comparison with the quantum theoretical result.

References in corpus (7)

• Spin Transfer Torques in MnSi at Ultra-low Current Densities
• Cubic magnets with Dzyaloshinskii-Moriya interaction at low T
• Persistent Spin Currents in Helimagnets
• Effects of Frustrated Surface in Heisenberg Thin Films
• Spin-Transfer Torque in Helical Spin-Density Waves
• Frustration Effects in Antiferromagnetic FCC Heisenberg Films
• Surface spin dynamics of antiferromagnetically coupled frustrated triangular films

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• Phase transition in frustrated thin films -- physics at phase boundaries
• Magneto-Ferroelectric Interaction in Superlattices: Monte Carlo Study of Phase Transitions
• Effectof biquadratic exchange on the phase diagram of a spin-1 transverse XY modelwith single-ion anisotropy
• Phase transition for a contact process with random slowdowns
• Quantum Spin-Wave Theory for non-collinear Spin Structures, a Review
• Partial phase transition and quantum effects in helimagnetic films under an applied magnetic field
• Monte Carlo Simulations of ABC Stacked Kagome Lattice Thin Films
• Effects of Dzyaloshinskii-Moriya interactions and dipole-dipole interactions on spin waves in finite-length ferromagnetic chains
• Tricriticality of the Blume-Emery-Griffiths Model In Thin Films of Stacked Triangular Lattices