Comment on "Physical Origin and Generic Control of Magnonic Band Gaps of Dipole-Exchange Spin Waves in Width-Modulated Nanostrip Waveguides" [K.-S. Lee, D.-S. Han, and S.-K. Kim, PRL 102, 127202 (2009), arXiv:0811.0411]

TL;DR

This paper critiques a previous study on magnonic bandgaps in nanostrip waveguides, revealing that incomplete excitation symmetry led to misleading conclusions, and offers a comprehensive analysis with multiple methods and group theory interpretation.

Contribution

It provides a complete magnonic band structure analysis using three different approaches, correcting prior omissions and clarifying the physical origin of bandgaps.

Findings

Full band structure confirms previous predictions with additional symmetry considerations

Multiple theoretical methods yield consistent results

Group theory offers physical insight into bandgap formation

Abstract

In Ref. [PRL 102, 127202 (2009)] Lee et al. reported the existence of large magnonic bandgaps in one-dimensional width-modulated Permalloy nanostripe waveguides based on OOMMF simulations. However, as the symmetry of the magnetic field pulse they applied to excite the spin waves (SWs) was not general, the entire set of SW branches with A symmetry was omitted from the magnonic band structures (see below). This omission has unfortunately led to misleading conclusions of, for instance, the number, width and position of the bandgaps. We present here the full band structure based on three different theoretical approaches that gave consistent predictions, thus corroborating the methods employed, namely, a microscopic approach, OOMMF simulations, and a method based on the linearized Landau-Lifshitz equation. Further, we provide a physical interpretation using group theory.