Spin dynamics simulations for a nanoscale Heisenberg antiferromagnetic film

Thermoinduced magnetization(TiM) is a novel response predicted to occur in nanoscale antiferromagnetic (AF) materials. Extensive Monte Carlo simulations\footnote{G. Brown, A. Janotti, M. Eisenbach, and G. M. Stocks, Phys.Rev.B {\bf 72}, 140405(2005)} have shown that TiM is an intrinsic property of the AF classical Heisenberg model. To obtain a fundamental understanding of TiM, spin dynamics (SD) simulations are performed to study the spin wave behavior, which seems to be the cause of TiM. A classical Heisenberg model with an AF nearest-neighbor exchange interaction and uniaxial single-site anisotropy is studied. Simple-cubic lattices with two free-surfaces and periodic boundaries parallel to the surfaces are used. We applied fast SD algorithms with 4th-order Suzuki-Trotter decompositions of the exponential operator. Discrete spin wave modes due to spin wave confinement\footnote{{\em Spin Wave Confinement}, edited by S. O Demokritov (Pan Stanford Publishing, Singapore, 2008)} are found in transverse S(q,\,$\omega$) in the perpendicular direction to free surfaces.