| This work investigates the dynamic response of nanospheres. We explore two seemingly different, but nonetheless conceptually related areas. Our first studies were directed toward the microwave response of nanoscale ferromagnetic spheres and arrays of such spheres, where spin excitations are of interest. Then we turn our attention to the collective plasmons of nanoscale metallic structures, and their influence on important aspects of the response of such systems. More specifically, we develop a theory to study dipole-exchange spin waves of ferromagnetic nanospheres. We show the influence of the dipole-dipole interaction and exchange interaction on the spin-wave resonance. Within this framework we also present a method to describe the collective spin-wave modes of arrays of ferromagnetic nanospheres. We explore the nature of the collective spin-wave spectrum of two dimensional arrays magnetized perpendicular to the plane, and also parallel to the plane. Issues examined are the dependence of collective spin-wave mode bandwidths on the lattice constant of the array, orientation of the magnetization, propagation direction of spin waves, and the size of the spheres. The last mentioned property controls the mode spectrum of the individual spheres through the influence of exchange. By knowing the normalized spin-wave eigenvectors from the theory we present, we then calculate the cross section of Brillouin light scattering from the dipole-exchange spin-waves modes of ferromagnetic nanospheres.; We also describe a method to analyze collective plasmon excitations associated with two nearby metallic nanospheres. Their spectrum depends oil the geometry and size of the system, the complex dielectric constant of the metals from which the spheres are fabricated. We explore the resonant electric fields between two objects enhanced by differently-polarized laser fields. We also present studies of the laser induced force between them, which we demonstrate can exceed the attractive van der Waal's force at resonance. This provides one to probe experimentally the collective plasmons between two metallic entities. |
