Introduction

The concept of spin waves was introduced by Bloch, who theoretically considered quantum states of exchanged-coupled spins slightly deviating from their equilibrium orientations. He found that these disturbances were dynamic: they propagate as waves through the medium. This chapter presents the basic classification of magnonic effects and emphasizes the propagating nature of spin wave excitations. In fact, due to the inevitably non-uniform magnetization and an internal magnetic field in confined magnetic systems, propagation of spin waves takes place in a non-uniform environment, which can be characterized by a graded index of refraction. The chapter addresses spin wave-/magnonic-coupled waveguides as the most promising candidates for effective channeling of spin waves between the functional units of magnonic networks. It investigates the spin wave dynamics in reconfigurable two-dimensional magnonic crystals. The chapter devotes to excitation and amplification of propagating spin waves by spin current microscopic waveguides by using the spintransfer torque effect.