Eur. Phys. J. B (2014) 87: 293
https://doi.org/10.1140/epjb/e2014-50504-7

Regular Article

Dynamic effects on the spin-wave spectrum of the bcc thin film

Faculty of Physics, Adam Mickiewicz University in Poznań, ul. Umultowska 85, 61-614 Poznań, Poland

^a e-mail: mamica@amu.edu.pl

Received: 25 July 2014
Received in final form: 27 October 2014
Published online: 8 December 2014

Abstract

In the present paper we consider a ferromagnetic thin film with exchange interaction between nearest and next-nearest neighbours. Using a microscopic model based on the Heisenberg Hamiltonian we investigate how the propagation parallel to the surface of the film affects the spin-wave spectrum. Due to its wave-vector dependence the effective coupling between lattice planes parallel to the surface can be of ferromagnetic or antiferromagnetic character, or it can vanish completely, depending on the propagation of spin waves. When the effective coupling vanishes, the film separates into subsystems in which spin waves propagate independently. Antiferromagnetic effective coupling for certain wave vectors implies reversed mode order in the spectrum (with the optical mode at the bottom and the acoustic one at the top). Interestingly, this effect occurs also when all the exchange interactions in the considered system are ferromagnetic.