Tunable Magneto-Optical Kerr Effects of Nanoporous Thin Films

Abstract

Magnetoplasmonics, combining magnetic and plasmonic functions, has attracted increasing attention owing to its unique magnetic and optical properties in various nano-architectures. In this work, Ag, CoFeB and ITO layers are fabricated on anodic aluminum oxide (AAO) porous films to form hybrid multi-layered nanoporous thin films by magnetron sputtering deposition process. The designed nanostructure supports localized surface plasmon resonance (LSPR) and tunable magneto-optical (MO) activity, namely, the sign inversion, which can be controlled by AAO porous film geometry (pore diameter and inter-pore spacing) flexibly. The physical mechanism of this special MO phenomena is further analyzed and discussed by the correlation of Kerr rotation and electronic oscillations controlled by the surface plasmon resonance that is related to the nanoporous structure.

Figure 1

Top-viewed SEM images of multi-layered nanoporous arrayed films deposited on six AAO templates with different geometries (a) S = 110 nm, D = 40 nm, (b) S = 110 nm, D = 60 nm, (c) S = 110 nm, D = 100 nm, (d) S = 450 nm, D = 130 nm, (e) S = 450 nm, D = 160 nm and (f) S = 450 nm, D = 200 nm.

Figure 2

(a) Angle tilted magnified SEM images of Ag (5 nm)/ITO (10 nm)/CoFeB (10 nm)/ITO (10 nm)/Ag (5 nm) nanoporous films on S = 110 nm, D = 60 nm AAO template, (b) scheme of the cross-section of nanofunnel films and (c) EDS of one of multi-layered nanoporous films suggesting that these films have Ag, Co, Fe, Sn, In, Al and O elements.

Figure 3

(a) P-MOKE and (b) L-MOKE loops of hybrid multi-layered nanoporous arrayed films deposited on six AAO templates with different geometries. (I) S = 110 nm, D = 40 nm; (II) S = 110 nm, D = 60 nm; (III) S = 110 nm, D = 100 nm; (IV) S = 450 nm, D = 130 nm; (V) S = 450 nm, D = 160 nm and (VI) S = 450 nm, D = 200 nm.

Figure 4

Absorbance intensity of hybrid multi-layered nanoporous arrayed films deposited on six AAO templates with different geometries. (I) S = 110 nm, D = 40 nm; (II) S = 110 nm, D = 60 nm; (III) S = 110 nm, D = 100 nm; (IV) S = 450 nm, D = 130 nm; (V) S = 450 nm, D = 160 nm and (VI) S = 450 nm, D = 200 nm. (a) Full range spectra. (b) Magnified local spectra with the vertical black line marks excitation at 660 nm.

Figure 5

(a) P-MOKE and (b) L-MOKE measurement configurations.