The effects of the ground-state magnetization on the dynamical properties of a two dimensional (2D) magnonic crystals represented by an array of antidot lattices (ADLs) are theoretically studied. ADLs are composed of circular nanoholes of diameter d = 200 nm, periodicity a = 610 nm embedded into a CoFeB film having thickness of 41 nm [1]. The analysis of collective modes has been carried out by means of a micromagnetic method, named Dynamical Matrix Method (DMM). The mode propagation is studied starting from two different ground state magnetization: a) applying an external magnetic field H along the z-axis and the Bloch wave vector K parallel to the x-axis, b) placing H along the y-axis and K parallel to the x-axis. The aim of this study is to describe the dynamic properties in terms of effective quantities and to investigate the influence of the two different ground state magnetizations on the dispersion relations. From the inspection of spatial profiles of collective modes it is identified, for both the static magnetization configurations, an effective wavelength commensurable with the periodicity a of the system which is related to the Bloch wavelength. Correspondingly, it is defined an effective wave vector k linked to the Bloch wave vector. It is found that, independently of the magnetization ground-state studied, a simple relation between the effective quantities and the Bloch quantities holds. It is demonstrated that the Bloch rule depending on the Bloch wave vector can be derived from the effective rule involving the effective wave vector independently of the ground-state magnetization [2,3]. On the other hand, other two characteristic physical quantities typical of collective modes like the group velocity and the band width strictly depend on the ground-state magnetization. In particular, the group velocity is higher for in-plane magnetization than for out-plane magnetization, while the band width behavior is reversed. A discussion of the possible reasons at the basis of the different trend of these physical quantities is also carried on. This work was partially supported by MIUR-PRIN 2010-11 Project2010ECA8P3 "DyNanoMag". [1] P. Malagò, L. Giovannini, and R. Zivieri, “Effective properties of perpendicularly magnetized 2D antidot lattices”, in press. [2] R. Zivieri and L. Giovannini, Metamaterials 6 (2012) e127. [3] R. Zivieri and L. Giovannini, Photon. Nanostruct: Fundam. Appl. 11 (2013) 191.
Dynamical properties of 2D ferromagnetic antidot lattices - Presentazione orale
MALAGO', Perla;GIOVANNINI, Loris;ZIVIERI, Roberto
2015
Abstract
The effects of the ground-state magnetization on the dynamical properties of a two dimensional (2D) magnonic crystals represented by an array of antidot lattices (ADLs) are theoretically studied. ADLs are composed of circular nanoholes of diameter d = 200 nm, periodicity a = 610 nm embedded into a CoFeB film having thickness of 41 nm [1]. The analysis of collective modes has been carried out by means of a micromagnetic method, named Dynamical Matrix Method (DMM). The mode propagation is studied starting from two different ground state magnetization: a) applying an external magnetic field H along the z-axis and the Bloch wave vector K parallel to the x-axis, b) placing H along the y-axis and K parallel to the x-axis. The aim of this study is to describe the dynamic properties in terms of effective quantities and to investigate the influence of the two different ground state magnetizations on the dispersion relations. From the inspection of spatial profiles of collective modes it is identified, for both the static magnetization configurations, an effective wavelength commensurable with the periodicity a of the system which is related to the Bloch wavelength. Correspondingly, it is defined an effective wave vector k linked to the Bloch wave vector. It is found that, independently of the magnetization ground-state studied, a simple relation between the effective quantities and the Bloch quantities holds. It is demonstrated that the Bloch rule depending on the Bloch wave vector can be derived from the effective rule involving the effective wave vector independently of the ground-state magnetization [2,3]. On the other hand, other two characteristic physical quantities typical of collective modes like the group velocity and the band width strictly depend on the ground-state magnetization. In particular, the group velocity is higher for in-plane magnetization than for out-plane magnetization, while the band width behavior is reversed. A discussion of the possible reasons at the basis of the different trend of these physical quantities is also carried on. This work was partially supported by MIUR-PRIN 2010-11 Project2010ECA8P3 "DyNanoMag". [1] P. Malagò, L. Giovannini, and R. Zivieri, “Effective properties of perpendicularly magnetized 2D antidot lattices”, in press. [2] R. Zivieri and L. Giovannini, Metamaterials 6 (2012) e127. [3] R. Zivieri and L. Giovannini, Photon. Nanostruct: Fundam. Appl. 11 (2013) 191.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
