Plasmon emission studies on nano-scale particulate recording materials

Abstract

The optical field emitted by radiatively decaying plasmons is studied for the case when the surface supporting the plasma excitations is that of a ferromagnetic metal rather than that of one of the commonly studied noble metals. Comparison is made between the phenomenon observed for plasmons travelling freely on a continuous conducting surface and those localized around nano-scale particles on an insulating substrate or embedded in a dielectric host. In the first case, structure mediated optical excitation on a nickel grating produces plasmons that travel away from their source becoming subject to a variety of decay mechanisms including radiative emission. Similarly, localized plasmons created in a cobalt longitudinal recording medium composed of particles having near mono-disperse magnetic volumes ≈7 × 10−25 m3 are likewise observed to re-emit optical radiation in a narrow beam at high non-specular angles consistent with radiative plasmon decay. Moreover, the plasmon mode structure supported by the particles, and which is reflected in the angular structure of the emitted radiation, appears indicative of the physical shape of the particles. The possible significance of plasmon behaviour in the development of ultra-high density recording media is highlighted.