We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.

Abstract:We introduce a novel magnetoplasmonic sensor concept for sensitive detection of refractive index changes. The sensor consists of a periodic array of Ni/ SiO 2 /Au dimer nanodisks. Combined effects of near-field interactions between the Ni and Au disks within the individual dimers and far-field diffractive coupling between the dimers of the array produce narrow linewidth features in the magneto-optical Faraday spectrum. We associate these features with the excitation of surface lattice resonances and show that they exhibit a spectral shift when the refractive index of the surrounding environment is varied. Because the resonances are sharp, refractive index changes are accurately detected by tracking the wavelength where the Faraday signal crosses 0. Compared to random distributions of pure Ni nanodisks or Ni/SiO 2 /Au dimers or periodic arrays of Ni nanodisks, the sensing figure of merit of the hybrid magnetoplasmonic array is more than one order of magnitude larger.

SrRuO 3 films have been grown in the tetragonal, structurally single-domain state under 1% of biaxial tensile strain. The angular dependencies of the magnetization and the magnetoresistance reveal an upright orientation of the tetragonal unit cell and biaxial magnetic in-plane anisotropy with 110 t easy axes. Reversible biaxial strain from piezoelectric Pb(Mg 1/3 Nb 2/3 ) 0.72 Ti 0.28 O 3 (PMN-PT) substrates has been applied to probe the direct strain response of the magnetization and the electrical resistance. At 1% tensile strain, the Curie temperature (T C ) and the ordered magnetic moment (m S ) at low temperatures are found to substantially decrease with further growing tensile strain. This suggests a suppression of m S resulting from distortions of the RuO 6 octahedra, in line with reported density-functional calculations. Reversible strain has also been applied to a film under weak tensile strain revealing the opposite response, i.e., an enhancement of T C and m S with tensile strain. Structural and magnetic properties of SrRuO 3 films in several static strain states (compressive, weak and strong tensile strain) are compared.

Transparent and metallic oxides based on 3d and 4d metals are promising materials for plasmonics. Here, the growth window to obtain epitaxial SrNbO3 (4d1) thin films is determined and the role of substrates to achieve optimal electrical conductivity and the largest residual resistivity ratio is disclosed. Optical measurements on optimized films indicate a large transparency at the visible with a sharp edge at about 1.9 eV, which coincides with the zero‐crossing of the permittivity, allowing to identify the plasma frequency ωp. Similar features are observed in SrVO3 (3d1) films. Optical losses display well pronounced maxima at the corresponding ωp. Polarization‐dependent optical transmittance measurements and ellipsometric data show a dip at ωp, occurring for p‐ but not s‐polarized light, which is a fingerprint of optical bulk plasmon excitation. Remarkably, plasmon resonance is achieved here by using oblique incidence of light rather than phase‐matching arrangements, and by exploiting charge density gradients at the film surface. This observation points to new opportunities for engineering plasmons in heterostructures.