Enhanced Magneto-Optical Edge Excitation in Nanoscale Magnetic Disks.

We report unexpected enhancements of the magneto-optical effect in ferromagnetic Permalloy disks of diameter D<400 nm. The effect becomes increasingly pronounced for smaller D, reaching more than a 100% enhancement for D=100 nm samples. By means of experiments and simulations, the origin of this effect is identified as a nanoscale ring-shaped region at the disk edges, in which the magneto-optically induced electric polarization is enhanced. This leads to a modification of the electromagnetic near fields and causes the enhanced magneto-optical excitation, independent from any optical resonance.

Crystallography-driven positive exchange bias in Co/CoO bilayers.

We have studied the temperature dependence of the exchange bias effect in epitaxial Co/CoO bilayer structures with in-plane uniaxial magnetocrystalline anisotropy. We have measured the anisotropic positive exchange bias, which is independent from the initial cooling field value. Synchronous with the occurrence of positive exchange bias, distinct changes in the magnetization reversal process indicate a temperature-dependent rotation of the effective anisotropy and exchange bias axis. Model calculations based upon the electron microscopy-determined epitaxial Co/CoO-interface structure corroborate this interpretation.