MAINZ Visiting Professorship Lectures Series: "Combined molecular dynamics-spin dynamics simulations of bcc iron"

A Mini-Course on Computer Simulation Methods in Condensed Matter Physics

Date: September 9th, 2015
Time: 9:15am (1h)
Location: Seminar room MAINZ, Staudinger Weg 9, third floor, room 03-122

Lecture by Prof. Dr. David P. Landau
Center for Simulational Physics, The University of Georgia, USA

Using a classical model that treats atomic and spin degrees of freedom on an equal footing, we study phonon-magnon interactions in BCC iron with combined molecular and spin Dynamics methods. The atomic interactions are modeled via a many-body potential while spin dependent interactions are established through a Hamiltonian of the Heisenberg form, with a distance dependent magnetic exchange interaction. The temporal evolution of atomic and spin degrees of freedom was determined by numerically solving the coupled equations of motion, using an algorithm based on second- order Suzuki-Trotter decomposition of exponential operators. By calculating Fourier transforms of space- and time-displaced correlation functions, we demonstrate that noticeable softening and damping of magnon modes occur due to the presence of lattice vibrations. As a result of the phonon-magnon coupling, we also observe an additional, narrow longitudinal spin wave excitation, with the same frequency as the longitudinal phonon mode for the corresponding wave vector. This predicted new mode poses a challenge for experimental study.