Functional Magnetic Waveguides For Magnonics

Magnonics, or spin wave based spintronics, is an emerging technology where magnons-quanta for spin waves-process the information analogous to electronic charges in electronics. We introduce the fundamental components of a magnonic device and briefly discuss their electrical control. The magnetic waveguide-an integral part of a magnonic circuit-guides the spin wave signal (magnon current) of desired frequency, wave vector, phase, and amplitude, which are the key ingredients for wave based computing. Typically, a bias magnetic field aligns magnetization to satisfy anisotropic magnon dispersions for low-energy and long-wavelength magnons, and thus it hinders on-chip device integration capability. We discuss strategies to eliminate the requirements of such a bias field by utilizing self-biased waveguides, which are based on either exchange coupled magnetic multi-layer based magnetic micro-wire or dipolar coupled but physically separated chain of rhomboid nanomagnets. We emphasize that the self-biased waveguides offer additional functionalities as compared to conventional waveguides. In this regard, manipulation of spin waves or the gating operation is presented by utilizing reconfigurable remanent magnetic states of the waveguide externally controlled by field or microwave current. We discuss the prospects of these bias-free waveguide strategies in the rapidly developing field of nano-magnonics and their potential for practical realizations of a magnonic-electronic hybrid technology.