Magnonic Crystals (MCs) represent a new class of metamaterials with periodically modulated magnetic properties where spin waves are used to carry and manipulate information, similarly to light in photonic crystals. These systems, indeed, can support propagation of collective spin excitations , whose dispersion is characterised by the presence of allowed magnonic states and ranges of forbidden frequencies (band gaps), related to the appearance of Brillouin Zones, induced by the artificial periodicity of the pattern geometry. Knowledge of the magnonic band structure of a specific MC is preliminary to any desired application. In this work, Brillouin Light Scattering (BLS) has been used to study the spin-wave band structure of a square array of cylindrical dots, 50 nm thick, having a diameter of 600 nm and interdot separation of 55 nm. BLS measurements were carried out applying the magnetic field H=1.0 kOe in the sample plane along the side of the square matrix and varying both the magnitude and in-plane direction of the transferred wave vector k. This allowed us to map the major symmetry directions of the first BZ: the Y (along which, k is perpendicular to H ), the X (along which, k is parallel to H ), the YM and the XM directions (along which, k has both a component parallel and perpendicular to H). We found that the fundamental mode (characterized by an almost uniform distribution of the dynamic magnetization) exhibits an oscillating behaviour. This indicates that, due to the dynamical dipolar interdot coupling, this mode propagates through the array as Bloch wave, characterized by a periodicity induced by the pattern symmetry. Experimental results have been satisfactorily reproduced by using the dynamical matrix method, which was extended to include the dipolar interaction in a 2-D array of dots. The dispersion relations are explained through the introduction of an effective wavevector that characterizes each mode in this metamaterial. This work was supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement n°228673 (MAGNONICS) and n°233552 (DYNAMAG).
Complete k-space mapping of collective modes in a 2-D metamaterial consisting of interacting NiFe nanodisks
MONTONCELLO, Federico;GIOVANNINI, Loris;ZIVIERI, Roberto;NIZZOLI, Fabrizio;
2011
Abstract
Magnonic Crystals (MCs) represent a new class of metamaterials with periodically modulated magnetic properties where spin waves are used to carry and manipulate information, similarly to light in photonic crystals. These systems, indeed, can support propagation of collective spin excitations , whose dispersion is characterised by the presence of allowed magnonic states and ranges of forbidden frequencies (band gaps), related to the appearance of Brillouin Zones, induced by the artificial periodicity of the pattern geometry. Knowledge of the magnonic band structure of a specific MC is preliminary to any desired application. In this work, Brillouin Light Scattering (BLS) has been used to study the spin-wave band structure of a square array of cylindrical dots, 50 nm thick, having a diameter of 600 nm and interdot separation of 55 nm. BLS measurements were carried out applying the magnetic field H=1.0 kOe in the sample plane along the side of the square matrix and varying both the magnitude and in-plane direction of the transferred wave vector k. This allowed us to map the major symmetry directions of the first BZ: the Y (along which, k is perpendicular to H ), the X (along which, k is parallel to H ), the YM and the XM directions (along which, k has both a component parallel and perpendicular to H). We found that the fundamental mode (characterized by an almost uniform distribution of the dynamic magnetization) exhibits an oscillating behaviour. This indicates that, due to the dynamical dipolar interdot coupling, this mode propagates through the array as Bloch wave, characterized by a periodicity induced by the pattern symmetry. Experimental results have been satisfactorily reproduced by using the dynamical matrix method, which was extended to include the dipolar interaction in a 2-D array of dots. The dispersion relations are explained through the introduction of an effective wavevector that characterizes each mode in this metamaterial. This work was supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement n°228673 (MAGNONICS) and n°233552 (DYNAMAG).I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
