An electric current controlled spin-wave logic gate based on a width-modulated dynamic magnonic crystal is realized. The device utilizes a spin-wave waveguide fabricated from a single-crystal Yttrium Iron Garnet film and two conducting wires attached
to the film surface. Application of electric currents to the wires provides a means for dynamic control of the effective geometry of the waveguide and results in a suppression of the magnonic band gap. The performance of the magnonic crystal as an AND logic gate is demonstrated.
Magnetism is a very fascinating and dynamic field. Especially in the last 30 years it has experienced many major advances in the full range from novel fundamental phenomena to new products. Applications such as hard disk drives and magnetic sensors a
re part of our daily life, and new applications, such as in non-volatile computer random access memory, are expected to surface shortly. Thus it is timely for describing the current status, and current and future challenges in the form of a Roadmap article. This 2014 Magnetism Roadmap provides a view on several selected, currently very active innovative developments. It consists of 12 sections, each written by an expert in the field and addressing a specific subject, with strong emphasize on future potential. This Roadmap cannot cover the entire field. We have selected several highly relevant areas without attempting to provide a full review - a future update will have room for more topics. The scope covers mostly nano-magnetic phenomena and applications, where surfaces and interfaces provide additional functionality. New developments in fundamental topics such as interacting nano-elements, novel magnon-based spintronics concepts, spin-orbit torques and spin-caloric phenomena are addressed. New materials, such as organic magnetic materials and permanent magnets are covered. New applications are presented such as nano-magnetic logic, non-local and domain-wall based devices, heat-assisted magnetic recording, magnetic random access memory, and applications in biotechnology. May the Roadmap serve as a guideline for future emerging research directions in modern magnetism.
Conversion of traveling magnons into an electron carried spin current is demonstrated in a time resolved experiment using a spatially separated inductive spin-wave source and an inverse spin Hall effect (ISHE) detector. A short spin-wave packet is ex
cited in a yttrium-iron garnet (YIG) waveguide by a microwave signal and is detected at a distance of 3 mm by an attached Pt layer as a delayed ISHE voltage pulse. The delay in the detection appears due to the finite spin-wave group velocity and proves the magnon spin transport. The experiment suggests utilization of spin waves for the information transfer over macroscopic distances in spintronic devices and circuits.
Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatiall
y-resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.
The operational characteristics of a magnonic crystal, which was fabricated as an array of shallow grooves etched on a surface of a magnetic film, were compared for magnetostatic surface spin waves and backward volume magnetostatic spin waves. In bot
h cases the formation of rejection frequency bands was studied as a function of the grooves depth. It has been found that the rejection of the volume wave is considerably larger than of the surface one. The influences of the nonreciprocity of the surface spin waves as well as of the scattering of the lowest volume spin-wave mode into higher thickness volume modes on the rejection efficiency are discussed.
One-dimensional magnonic crystals have been implemented as gratings of shallow grooves chemically etched into the surface of yttrium-iron garnet films. Scattering of backward volume magnetostatic spin waves from such structures is investigated experi
mentally and theoretically. Well-defined rejection frequency bands are observed in transmission characteristics of the magnonic crystals. The loss inserted by the gratings and the rejections bands bandwidths are studied as a function of the film thickness, the groove depth, the number of grooves, and the groove width. The experimental data are well described by a theoretical model based on the analogy of a spin-wave film-waveguide with a microwave transmission line. Our study shows that magnonic crystals with required operational characteristics can be engineered by adjusting these geometrical parameters.
Bose-Einstein condensation in a gas of magnons pumped by an incoherent pumping source is experimentally studied at room temperature. We demonstrate that the condensation can be achieved in a gas of bosons under conditions of incoherent pumping. Moreo
ver, we show the critical transition point is almost independent of the frequency spectrum of the pumping source and is solely determined by the density of magnons. The electromagnetic power radiated by the magnon condensate was found to scale quadratically with the pumping power, which is in accordance with the theory of Bose-Einstein condensation in magnon gases.
