Interaction effects on the magneto-optical response of magnetoplasmonic dimers

N. de Sousa, L. S. Froufe-Pérez, G. Armelles, A. Cebollada, M. U. González, F. García, D. Meneses-Rodríguez, and A. García-Martín

Phys. Rev. B 89, 205419 – Published 19 May 2014

Abstract

The effect that dipole-dipole interactions have on the magneto-optical (MO) properties of magnetoplasmonic dimers is theoretically studied. The specific plasmonic versus magnetoplasmonic nature of the dimer's metallic components and their specific location within the dimer play a crucial role in the determination of these properties. We find that it is possible to generate an induced MO activity in a purely plasmonic component, even larger than that of the MO one, therefore dominating the overall MO spectral dependence of the system. Adequate stacking of these components may allow one to obtain, for specific spectral regions, larger MO activities in systems with a reduced amount of MO metal and therefore with lower optical losses. Theoretical results are contrasted and confirmed with experiments for selected structures.

Received 19 December 2013
Revised 25 April 2014

DOI:https://doi.org/10.1103/PhysRevB.89.205419

Authors & Affiliations

N. de Sousa

Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, E-28049 Madrid, Spain

L. S. Froufe-Pérez

Instituto de Estructura de la Materia, CSIC, Serrano 121, E-28006 Madrid, Spain

G. Armelles, A. Cebollada, M. U. González, F. García, D. Meneses-Rodríguez, and A. García-Martín^*

IMM-Instituto de Microelectrónica de Madrid (CNM-CSIC), Issac Newton 8, PTM, E-28760 Tres Cantos, Madrid, Spain

^*a.garcia.martin@csic.es

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Vol. 89, Iss. 20 — 15 May 2014

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Images

Figure 1
Schematic representation of the studied configurations. (a) The lower dipole is MP, whereas the upper one is P. (b) The lower dipole is P, whereas the upper disk is MP. (c) Both disks are MP.
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Figure 2
Dipole contributions, and MOA for 0.1% Co concentration. (a)–(c) $x$ component of the scaled dipole (left axis) and the cosine of the relative phase between them (right axis). (d)–(f) $y$ component of the scaled dipole (left axis) and their relative phase (right axis). (g)–(i) Magneto-optical activity. The upper panels represent the situation where the MP dipole is at the bottom, the medium panels show when the MP dipole is at the top, and the lower panels show when both are MP. Triangle up for the top dipole, and triangle down for the bottom dipole.
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Figure 3
Dipole contributions, and MOA for 25% Co concentration. (a)–(c) $x$ component of the scaled dipole (left axis) and the cosine of the relative phase between them (right axis). (d)–(f) $y$ component of the scaled dipole (left axis) and their relative phase (right axis). (g)–(i) Magneto-optical activity. The upper panels represent the situation where the MP dipole is at the bottom, the middle panels show when the MP dipole is at the top, and the lower panels show when both are MP. Triangle up for the top dipole, and triangle down for the bottom dipole
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Figure 4
(a) Experimental results and (b) numerical simulations of the MO activity when the MP disk is at the bottom. (c),(d) are the same, but when the MP disk is at the top, and (e),(f) show when both are MP. In the rightmost panel, we show atomic force microscopy (AFM) images of the three experimental samples where the density of disks (about 15% coverage) and homogeneity can be seen. The images show that the disk diameter ranges from 130 to 150 nm. Also represented is a scheme of the structures. We depict the Ti adhesive layer (green), the Co layers (blue), the SiO $_{2}$ (gray), and the gold layers (yellow). The three different systems are constituted by two metallic disks separated by 20 nm of SiO $_{2}$ . For the configuration with the MP disk at the bottom (upper panel), the MP disk is composed of a 2 nm Ti layer followed by a 4 nm Au layer and three sequential combinations of 2 nm Co/4 nm Au layers. The disk at the top is composed of 16 nm Au. For the configuration with the MP disk at the top (middle panel), the MP disk is composed of an initial 1 nm layer of Ti, then 4 nm Au layer and two sequences of 2 nm Co/4 nm Au layers. The disk at the bottom is composed of 22 nm of gold. When both disks are MP (lower panel), they consist of those Au/Co sequences employed in the other two situations.
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