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In this ‘focus on’ collection, a snapshot of the new, fast emerging field of magnetoplasmonics is presented. The research in the field deals with the combination of plasmonics and magnetism to elucidate the fundamentals of spin--plasmon interactions and reach new functionalities such as the enhancement of magneto-optical activity in various materials, active control of plasmons with weak magnetic fields, magnetoplasmonics-based bio- and chemical sensing, magnetophotonic and magnetoplasmonic crystals as modulators of light transmission and reflection, and many others.

The use of plasmonic and magnetoplasmonic interferometers as refractometric-based sensors is studied theoretically, and their performance compared to that of the most commonly used plasmonic sensing technique, the surface plasmon resonance (SPR) sensor. The analysis is based on the evolution with the refractive index of the physical parameters involved for each kind of sensor, as well as the behaviour of the actual measured quantity. Two kinds of sensing configurations, two-dimensional surface and three-dimensional bulk, are considered, and the spectral dependence of the three systems is also taken into account. We show that, although the plasmonic interferometer and the SPR system are based on the same physical parameter, namely the surface plasmon polariton (SPP) wavevector, the first offers better properties as its final sensitivity depends on the interferometer size and can thus be increased by its enlargement. For the magnetoplasmonic interferometer, on the other hand, a new physical parameter participates—the modulation of the SPP wavevector induced by an external applied magnetic field. This new parameter has a higher sensitivity to the refractive index than the SPP wavevector, so monitoring it can lead to sensors with increased properties.

The magnetic-field-induced wave-vector modulation of surface plasmon polaritons (SPPs) is analytically derived for dielectric/metal and dielectric/metal/dielectric systems when a very thin magneto-optical metallic film is placed at different positions in the metal. In the simplest case of a single dielectric/metal interface, the SPP wave-vector modulation is found to be proportional to the intensity of the electromagnetic field at the location of the magneto-optically active layer. For the more complex dielectric/metal/dielectric systems, the SPPs existing at each dielectric/metal interface interact to give rise to modes with a symmetric- and anti-symmetric-like character. We show that in this case the relationship between wave-vector modulation and field distribution is more complex and does not follow a proportionality law for coupled eigenmodes.