Andrii V. Chumak

Magnon transistor for all-magnon data processing

An attractive direction in next-generation information processing is the development of systems employing particles or quasiparticles other than electrons—ideally with low dissipation—as information carriers. One such candidate is the magnon: the quasiparticle associated with the eigen-excitations of magnetic materials known as spin waves. The realization of single-chip all-magnon information systems demands the development of circuits in which magnon currents can be manipulated by magnons themselves. Using a magnonic crystal—an artificial magnetic material—to enhance nonlinear magnon–magnon interactions, we have succeeded in the realization of magnon-by-magnon control, and the development of a magnon transistor. We present a proof of concept three-terminal device fabricated from an electrically insulating magnetic material. We demonstrate that the density of magnons flowing from the transistor’s source to its drain can be decreased three orders of magnitude by the injection of magnons into the transistor’s gate.

The 2014 Magnetism Roadmap

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 are 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.

A current-controlled, dynamic magnonic crystal

We present a current-controlled magnonic crystal consisting of a ferrite film in which spin waves propagate and a set of parallel, periodically spaced, current conducting stripes placed close to the film surface. The current flow causes a sine-like variation of the films internal magnetic field, which can be modulated by changing the amount of current. Transmission measurements reveal a single, pronounced rejection band. With increasing current strength the rejection band depth and its width increase strongly. Moreover, it is possible to switch the artificial, periodic structure on and off, so that the waveguide makes a transition from full rejection to full transmission within less than 50 ns. Numerical simulations confirm the experimental results and show that the spin-wave propagation in the crystal can be effectively described as a scattering process in the first Born approximation. Three ways to increase the reflection efficiency of the magnonic crystal are identified: an increased number of periods, an increased lattice constant and a decreased spacing between the current carrying structure and the waveguide.

Design of a spin-wave majority gate employing mode selection

The design of a microstructured, fully functional spin-wave majority gate is presented and studied using micromagnetic simulations. This all-magnon logic gate consists of three-input waveguides, a spin-wave combiner and an output waveguide. In order to ensure the functionality of the device, the output waveguide is designed to perform spin-wave mode selection. We demonstrate that the gate evaluates the majority of the input signals coded into the spin-wave phase. Moreover, the all-magnon data processing device is used to perform logic AND-, OR-, NAND- and NOR- operations.

Unidirectional spin-wave heat conveyer.

When energy is introduced into a region of matter, it heats up and the local temperature increases. This energy spontaneously diffuses away from the heated region. In general, heat should flow from warmer to cooler regions and it is not possible to externally change the direction of heat conduction. Here we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic Y3Fe5O12, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes without time-reversal symmetry and to the conversion of spin waves into heat. When a Y3Fe5O12 film with low damping coefficients is used, spin waves are observed to emit heat at the sample end up to 10 mm away from the excitation source. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller.

Thickness and power dependence of the spin-pumping effect in Y3Fe5O12 /Pt heterostructures measured by the inverse spin Hall effect

The dependence of the spin-pumping effect on the yttrium iron garnet

Spin-wave logic devices based on isotropic forward volume magnetostatic waves

({\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}

A micro-structured ion-implanted magnonic crystal

, YIG) thickness detected by the inverse spin Hall effect (ISHE) has been investigated quantitatively. Due to the spin-pumping effect driven by the magnetization precession in the ferrimagnetic insulator

Sign of inverse spin Hall voltages generated by ferromagnetic resonance and temperature gradients in yttrium iron garnet platinum bilayers

{\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}

A spin-wave logic gate based on a width-modulated dynamic magnonic crystal

film a spin-polarized electron current is injected into the Pt layer. This spin current is transformed into electrical charge current by means of the ISHE. An increase of the ISHE voltage with increasing film thickness is observed and compared to the theoretically expected behavior. The effective damping parameter of the YIG/Pt samples is found to be enhanced with decreasing