Surface plasma resonance (SPR) excitation in a Co-based two-dimensional magnetoplasmonic crystal was found to strongly enhance the second-harmonic generation (SHG) efficiency. Large changes in the phase shift between magnetic and nonmagnetic SHG contributions were observed in the transversal Kerr effect as a function of the incidence angle. The activation of a nonlocal quadrupole mechanism of the magnetic SHG due to the SPR excitation was found to lead to an unusual phase behavior in the vicinity of the resonance.
We combine transport measurements and magneto-optical imaging in order to study vortex motion in Pb samples with a square lattice of asymmetric pinning potentials formed by two antidots of different sizes. Near the boundary with the normal phase, a vortex ratchet effect is detected when an ac-current is applied. As previously observed in similar systems, inversion of vortex rectification direction occurs as the magnetic field is changed. Further inside the superconducting phase, anisotropic flux penetration patterns are formed. An inversion of anisotropy is observed as the temperature is lowered. This effect can be understood in terms of a thermomagnetic avalanche model.
We investigate the flux penetration in Pb films, of different shapes, deposited on top of a periodic array of Co/ Pt dots with perpendicular anisotropy by means of magnetization and magneto-optical measurements. A clear dependence of the critical current density on the magnetic state of the dots and their polarity with respect to the direction of the applied magnetic field is observed by both techniques. The magnetic state of the dots changes the flux penetration from smooth to channelling. Additionally, in the fully magnetized state, an anisotropic current distribution is observed in circular-shaped samples. The flux penetration is dominated by avalanches only for configurations which correspond to a high critical current, irrespective of its origin, be it low temperature, magnetization state of the dots, or angle between the lattice of dots and the edge of the sample.
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