Plasmon-enhanced magneto-optical activity in ferromagnetic membranes

Abstract

Experimental and theoretical evidence of plasmon-enhanced Kerr rotation in purely ferromagnetic membranes with sufficiently small dimensions to be out of extraordinary optical transmission conditions ͑45 nm pore diameter, 90nm lattice constant͒, is reported in this work. It is shown that the spectral location of the enhanced Kerr rotation region varies as the refractive index of the material inside the pore is modified. A similar behavior is obtained if the pore radius changes while keeping the pore concentration unchanged. Those are clear signatures indicating that localized surface plasmon resonances propagating along the pores govern the magneto-optical response of the membrane. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3167297͔ Nanoholed ferromagnetic membranes are attracting a great deal of interest over the last years due to their unique magnetic behavior. [1][2][3][4][5][6] Their magnetic properties are strongly influenced by the precise geometry of the nanostructure, namely the pore diameter and the interpore distance since these parameters control the nucleation and movement of domain walls as well as induce locally distributed magnetic anisotropies absent in unpatterned films. 7,8 From an applied viewpoint, ferromagnetic membranes can be used for developing data storage media based on domain wall structures as well as advanced sensing devices. 1,2,9On a different context, membranes made of noble metals have been deeply studied since they exhibit anomalous optical responses resulting from the excitation of plasmons in the nanostructures, such as the extraordinary optical transmission ͑EOT͒ bands observed in metallic patterned thin films with arrays of subwavelength holes. 10 There have been attempts to control this EOT using liquid crystals 11 or exploiting the intrinsic magneto-optical ͑MO͒ activity present in every metal, 12,13 although this would require huge magnetic fields for the nonferromagnetic membranes. Belotelov et al. 14 have used these extraordinary effects to modify the response of nonstructured MO materials, e.g., using Au film with subwavelength holes array deposited on top of a Bismuth substituted Yttrium Iron garnet ͑BiYIG͒ film. In the spectral region where the EOT takes place, the MO response ͑Kerr signal͒ shows an increase with respect to that of an unpatterned film, which is attributed to the purely optical effect of strong decrease of the reflectance.Ferromagnetic nanostructures have shown interesting optical and MO properties related to the excitation of surface plasmons as shown in ordered arrays of Ni nanowires embedded in an alumina matrix. 15,16 In these nanostructures, the plasmons, propagating along the wires, were responsible of the observed MO response enhancement that has not merely optical origin. Diwekar et al. 17 observed the existence of EOT bands in Co films with subwavelength hole arrays ͑150 nm diameter, 300 nm periodicity͒, which was explained as due to light coupling to surface plasmons on the two film interfaces. Quite recently, Ctistis et al. 18 ha...

Magnetoplasmonics: Combining Magnetic and Plasmonic Functionalities

“…Figure 12 (a) shows a sketch and SEM image of such membrane, with indication of the membrane lattice parameters. [ 154 ] . Figure 12 (c) presents the effect on the TMOKE signal.…”

Magnetic properties engineering of nanopatterned cobalt antidot arrays

“…Magnetic antidot arrays are groups of ordered holes created on a continuous magnetic film. They are being intensively investigated as candidates for high-density storage media [1,2], magnonic crystals with potential application in microwave devices [3,4], magnetically-active plasmonics [5], and lately for magnetic biosensing applications [6].…”

Nonreciprocal hybrid magnetoplasmonics

“…In contrast to continuous films, periodically corrugated systems allow the excitation of SPP resonances and enhanced MO response without a prism coupler [171][172][173][174][175][176][177]. This aspect makes such systems much more suitable for the integration in an ultra-compact environment.…”