Magneto-optical manipulation of surface plasmons in
gold/ferromagnetic/gold multilayer films
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Citation
Temnov, V.V., et al. “Magneto-optical Manipulation of Surface
Plasmons in Gold/ferromagnetic/gold Multilayer Films.” Lasers
and Electro-Optics, 2009 and 2009 Conference on Quantum
Electronics and Laser Science Conference. CLEO/QELS 2009.
Conference On. 2009. 1-2.© 2009 IEEE.
As Published
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=52257
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Institute of Electrical and Electronics Engineers
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Accessed
Fri May 27 00:13:35 EDT 2016
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http://hdl.handle.net/1721.1/62553
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a2234_1.pdf
CMJJ2.pdf
CMJJ2.pdf
IMK2.pdf
© 2009 OSA/CLEO/IQEC 2009
Magneto-optical manipulation of surface plasmons
in gold/ferromagnetic/gold multilayer films
V.V. Temnov
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
Phone: (617) 452-2594, Fax: (617) 253-6295, e-mail: temnov@mit.edu
U. Woggon
Institut für Optik und Atomare Physik, TU Berlin, Strasse des 17. Juni 135, 10632 Berlin, Germany
D. Guzatov
Research Center of the Resource Saving Problems, NAS Belarus, Tyzenhauz sq. 7, Grodno 230023
Belorussia
G. Armelles, A. Cebollada, A. Garcia-Matrin, and J.M. Garcia-Martin
Instituto de Microelectrónica de Madrid (CSIC), 28760-Tres Cantos, Madrid, Spain
T. Thomay, A. Leitenstorfer, and R. Bratschitsch
Department of Physics and Center for Applied Photonics, University of Konstanz,
D-78457 Konstanz, Germany
Abstract: Modulation of the surface plasmon wave vector in composite
Gold/Cobalt/Gold multilayer films due to periodic magnetization switching in Cobalt is
observed with a tilted slit-groove microinterferometer.
©2008 Optical Society of America
OCIS Codes: 240.6680, 260.3910
Magneto-optical effects are extensively used in nano-plasmonics both for the investigation of magnetooptical activity in composite nanostructures and sensing applications. The most widespread experimental
geometry exploits phase-matched surface plasmon excitation in Kretschmann geometry for a thin metallic
(or metallic composite) film on a dielectric prism. Due to phase-matched surface plasmon excitation very
large field enhancements can be achieved which drastically enhance the measurement sensitivity, giving
access to weak magneto-optical effects. However, in Kretchmann geometry it is difficult to determine
whether the change of the magneto-optical signal is caused by modification of the surface plasmon wave
vector or by absorption.
Here, we investigate the magneto-optical response in composite Gold/Cobalt/Gold multilayer films by
means of surface plasmon interferometry. Our novel design of a plasmonic microinterferometer consists of
a tilted slit-groove pair patterned by focused ion beam milling in a 200 nm thin multilayer metal film (Fig.
1). The length of both slits and grooves is 50 µm. The slit has a width of 100 nm. Grooves are 100 nm deep
and 200 nm wide. The slit-groove tilt angle was varied between 3 and 10 degrees, and the slit-groove
distance varies between 0 to 50 microns. In contrast to parallel slit-groove arrangements, a small tilt angle
between the slit and the groove favors interferometric measurements at a single wavelength. Illumination of
the plasmon interferometer with a collimated p-polarized continuous-wave beam of a laser diode at normal
incidence (100 mW @ 808 nm, beam diameter ~30 µm FWHM) results in the excitation of surface
plasmons launched by the groove. The plasmons propagate towards the slit where they are reconverted into
free-space radiation and interfere with light directly transmitted through the slit (Fig. 1(b)). The resulting
plasmonic interference pattern along the slit is shown in the upper panel of Fig. 1(c). The spatial period of
the intensity modulation is proportional to the slit-groove tilt angle. The key idea behind surface plasmon
interferometry is to modify the optical properties of the medium between the slit and the groove. As a
consequence, the contrast and phase shift of the plasmonic interference pattern observed at the slit position
are modified. To do this, we apply a periodic external magnetic field with a few tens of mT and direction
parallel to the slit axis to switch the magnetization in the Cobalt layer. We record the magneto-optical
(MO) signal with a lock-in amplifier at every position along the slit (Fig. 1c).
978-1-55752-869-8/09/$25.00 ©2009 IEEE
a2234_1.pdf
CMJJ2.pdf
CMJJ2.pdf
IMK2.pdf
© 2009 OSA/CLEO/IQEC 2009
Fig. 1: Schematic drawing of the plasmonic microinterferometer consiting of a tilted slit-groove pair patterned by a
focused ion beam in a composite magneto-optically active Au/Co/Au multilayer film (a, b) and results of
magnetoplasmonic interferometry (c) demonstrating the effect of magnetization switching in the Cobalt layer on the
optical properties of surface plasmons (see text for details).
The recorded MO signal has the same spatial period as the plasmonic interferogram itself. The pronounced
phase shift φ (0<φ<π/2) between the intensity and MO-signal indicates that both surface plasmon wave
vector and absorption change upon magnetization switching. Whereas a change in absorption would
primarily modify the contrast of the plasmonic interference pattern (φ=0), the change of surface plasmon
wave vector would shift the interference fringes (φ=π/2). Obviously, our technique can easily distinguish
between these two contributions which are usually hidden in Kretchmann geometry. The lowest panel in
Fig. 1(c) shows the MO-signal normalized to the contrast of the plasmonic interference pattern. As
expected, the MO-signal is proportional to the slit-groove spacing which linearly increases along the slit
due to the slit-groove tilt angle (dashed lines in Fig. 1(c)). The above conclusions are supported by
interferometric measurements in plasmonic microinterferometers with different slit-groove spacings and tilt
angles.
In conculusion, we have demonstrated a new tool to analyze the influences of ferromagnetic switching in a
metallic multilayer structure on the transport properties of surface plasmons. Changes in the dispersive and
absorptive parts of the propagation constant are clearly distinguished. The analysis of our experimental data
obtained for samples with different geometries reveal the dependence of the MO-signal depth of the Cobalt
layer below a gold-air interface. This effect is compared with the results of theoretical calculations and
physical implications for magneto-optics in composite multilayer films will be discussed.