On magnon energy branches of multilayer ferrimagnetic superlattices [Reply to the comment “Boson Green's functions treatment of three‐layer ferrimagnetic superlattice”, phys. stat. sol. (b) 244, No. 10, 3750–3753 (2007)

Abstract

AbstractThe magnon energy branches of multilayer ferrimagnetic superlattices are discussed, as regards the linear spin‐wave approach and Green's function technique. It is argued that negative energy branches in the spin‐wave spectra of the ferrimagnetic systems have physical significance, which is responsible for the zero‐point motion (i.e. the quantum fluctuations) in the ground state, since the sign of ωl(k) indicates the direction in which the spin‐wave mode propagates. On boson Green's function treatment, the results calculated for physical properties with consideration of negative energy spectra are correct and the consequent conclusions do not need to be re‐examined. Even for the definition of energy gaps, nothing is wrong from the theoretical point of view if one considers both negative and positive energy spectra, but one may need to consider two different definitions (one considers the negative/positive energy spectra; the other only the positive ones), from the experimental point of view, to compare both of them with experimental data, in an attempt to detect whether the negative energy branch does excite or not. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)