2008/04/30 by T. Huberman, D. A. Tennant, D. M. Tennant +4
Physics and Astronomy · #Advanced Condensed Matter Physics #Magnetic properties of thin films #Physics of Superconductivity and Magnetism #cond-mat.stat-mech
paper · pdf · doi:10.1088/1742-5468/2008/05/p05017
published as J. Stat. Mech. (2008) P05017 · 28 pages 20 figures, Published in J. Stat. Mech. (2008) P05017 without changes
openalex publication_date 2008/05/30 · arxiv created 2008/06/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
We report comprehensive inelastic neutron scattering measurements of the magnetic excitations in the 2D spin-5/2 Heisenberg antiferromagnet Rb 2 MnF 4 as a function of temperature from deep in the Néel ordered phase up to paramagnetic, 0.13< k B T /4 JS <1.4. Well-defined spin waves are found for wavevectors larger than the inverse correlation length ξ −1 for temperatures up to near the Curie–Weiss temperature, Θ CW . For wavevectors smaller than ξ −1 , relaxational dynamics occurs. The observed renormalization of spin wave energies, and evolution of excitation lineshapes, with increasing temperature are quantitatively compared with finite-temperature spin wave theory and computer simulations for classical spins. Random phase approximation calculations provide a good description of the low temperature renormalization of spin waves. In contrast, lifetime broadening calculated using the first Born approximation shows, at best, modest agreement around the zone boundary at low temperatures. Classical dynamics simulations using an appropriate quantum classical correspondence were found to provide a good description of the intermediate and high temperature regimes over all wavevector and energy scales, and the crossover from quantum to classical dynamics observed around Θ CW / S , where the spin S = 5/2. A characterization of the data over the whole wavevector/energy/temperature parameter space is given. In this, T 2 behaviour is found to dominate the wavevector and temperature dependence of the linewidths over a large parameter range, and no evidence of hydrodynamic behaviour or dynamical scaling behaviour found within the accuracy of the datasets. An efficient and easily implemented classical dynamics methodology is presented that provides a practical method for modelling other semiclassical quantum magnets.