Generation of propagating spin waves from regions of increased dynamic demagnetising field near magnetic antidots

Journal article and accompanying data and mediaThe article appeared in Applied Physics Letters 107, 162401 (2015); doi: 10.1063/1.4933263 and may be found at http://dx.doi.org/10.1063/1.4933263We have used Brillouin Light Scattering and micromagnetic simulations to demonstrate a point-like source of spin waves created by the inherently nonuniform internal magnetic field in the vicinity of an isolated antidot formed in a continuous film of yttrium-iron-garnet. The field nonuniformity ensures that only well-defined regions near the antidot respond in resonance to a continuous excitation of the entire sample with a harmonic microwave field. The resonantly excited parts of the sample then served as reconfigurable sources of spin waves propagating (across the considered sample) in the form of caustic beams. Our findings are relevant to further development of magnonic circuits, in which point-like spin wave stimuli could be required, and as a building block for interpretation of spin wave behavior in magnonic crystals formed by antidot arrays.Engineering and Physical Sciences Research Council (EPSRC)Russian Foundation for Basic ResearchRussian Science FoundationScholarship of the President of Russian Federatio

Field-Controlled Phase-Rectified Magnonic Multiplexer

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this record.The article plus associated .mif files is in ORE: http://hdl.handle.net/10871/18265The mechanism used to alter the features of propagating spin waves is a key component underpinning the functionality of high-frequency magnonic devices. Here, using experiment and micromagnetic simulations, we demonstrate the feasibility of a magnonic multiplexer in which the spin-wave beam is toggled between device output branches by the polarity of a small global bias magnetic field. Due to the anisotropy inherent in the dispersion of magnetostatic spin waves, the phase fronts of the output spin waves are asymmetrically tilted relative to the direction of the beam propagation (group velocity). We show how the phase tilts could be (partly) rectified in the magnonic waveguides of variable widths.This work was supported in part by the U.K. Engineering and Physical Sciences Research Council under Project EP/L019876/1 and Project EP/P505526/1, in part by the Russian Science Foundation under Project 14–19-00760, in part by the Scholarship of the President of Russian Federation (SP-313.2015.5), and in part by the Russian Foundation under Projects 14-07-00273 and 15-37-51253

Magnonic beam splitter: The building block of parallel magnonic circuitry

We demonstrate a magnonic beam splitter that works by inter-converting magnetostatic surface and backward-volume spin waves propagating in orthogonal sections of a T-shaped yttrium iron garnet structure. The inter-conversion is enabled by the overlap of the surface and volume spin wave bands. This overlap results from the demagnetising field induced along the transversely magnetised section(-s) of the structure and the quantization of the transverse wave number of the propagating spin waves (which are therefore better described as waveguide modes). In agreement with numerical micromagnetic simulations, our Brillouin light scattering imaging experiments reveal that, depending on the frequency, the incident fundamental waveguide magnonic modes may also be converted into higher order waveguide modes. The magnonic beam splitter demonstrated here is an important step towards the development of parallel logic circuitry of magnonics.The research leading to these results has received funding from the Russian Foundation for Basic Research (Project No. 14-07-00273), the Grant from Russian Science Foundation (Project No. 14-19-00760), the Scholarship of the President of Russian Federation (SP-313.2015.5), and from the Engineering and Physical Sciences Research Council of the United Kingdom (Project Nos. EP/L019876/1 and EP/P505526/1)

Dynamic imaging of the delay- and tilt-free motion of Néel domain walls in perpendicularly magnetized superlattices

We report on the time-resolved investigation of current- and field-induced domain wall motion in the flow regime in perpendicularly magnetized microwires exhibiting anti-symmetric exchange interaction by means of scanning transmission x-ray microscopy using a time step of 200 ps. The sub-ns time step of the dynamical images allowed us to observe the absence of incubation times for the motion of the domain wall within an uncertainty of 200 ps, together with indications for a negligible inertia of the domain wall. Furthermore, we observed that, for short current and magnetic field pulses, the magnetic domain walls do not exhibit a tilting during its motion, providing a mechanism for the fast, tilt-free, current-induced motion of magnetic domain walls

Frequency-selective spin-wave propagation in magnonic waveguide with a local laser-heated region

This is the final version. Available from the American Physical Society via the DOI in this record. We report on the spin-wave propagation along a magnonic waveguide with a local area of decreased magnetization, which is induced by heating produced with a focused laser spot. A phase-sensitive Brillouin light scattering technique is used to image how the spin wave propagates along the waveguide with a local heat landscape. Frequency-selective signal propagation along the waveguide is demonstrated. Micromagnetic simulations reveal intermodal interference variation in the region after the heated area. The proposed way to reconfigure the magnetization landscape can be used in magnonic devices with frequency-selective spin-wave transport.Russian Science Foundatio

Erratum: Towards graded-index magnonics: Steering spin waves in magnonic networks [Phys. Rev. B 92, 020408(R) (2015)]

This is the final version of the article. Available from the American Physical Societ via the DOI in this record.This is the erratum to 'Towards graded-index magnonics: Steering spin waves in magnonic networks'. Physical Review B 92, 020408(R), 20 July 2015. DOI: https://doi.org/10.1103/PhysRevB.92.020408The article for which this is the erratum is in ORE: http://hdl.handle.net/10871/26167-The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 247556 (NoWaPhen), from the Engineering and Physical Sciences Research Council of the United Kingdom under Projects No. EP/L019876/1 and No. EP/L020696/1, from Russian Science Foundation (Project No. 14-19-00760), and the Scholarship of the President of Russian Federation (SP-313.2015.5)

Pinning and hysteresis in the field dependent diameter evolution of skyrmions in Pt/Co/Ir superlattice stacks

We have imaged N\'eel skyrmion bubbles in perpendicularly magnetised polycrystalline multilayers patterned into 1 \mu m diameter dots, using scanning transmission x-ray microscopy. The skyrmion bubbles can be nucleated by the application of an external magnetic field and are stable at zero field with a diameter of 260 nm. Applying an out of plane field that opposes the magnetisation of the skyrmion bubble core moment applies pressure to the bubble and gradually compresses it to a diameter of approximately 100 nm. On removing the field the skyrmion bubble returns to its original diameter via a hysteretic pathway where most of the expansion occurs in a single abrupt step. This contradicts analytical models of homogeneous materials in which the skyrmion compression and expansion are reversible. Micromagnetic simulations incorporating disorder can explain this behaviour using an effective thickness modulation between 10 nm grains

Spin wave propagation in a uniformly biased curved magnonic waveguide

This is the final version of the article. Available from American Physical Society via the DOI in this record.Using Brillouin light scattering microscopy and micromagnetic simulations, we study the propagation and transformation of magnetostatic spin waves across uniformly biased curved magnonic waveguides. Our results demonstrate that the spin wave transmission through the bend can be enhanced or weakened by modifying the distribution of the inhomogeneous internal magnetic field spanning the structure. Our results open up the possibility of optimally molding the flow of spin waves across networks of magnonic waveguides, thereby representing a step forward in the design and construction of the more complex magnonic circuitry.Structure fabrication and microwave measurements were supported by a grant from the Russian Science Foundation (Grant No. 16-19-10283). This work was also partially supported by the Russian Foundation for Basic Research (Grant No. 16-37-00217), the Scholarship and Grant of the President of RF (Grant No. SP-313.2015.5, MK-5837.2016.9), and the Engineering and Physical Sciences Research Council of the United Kingdom (Projects No. EP/L019876/1 and No. EP/P505526/1)

Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers

Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterised by an angle with respect to the applied force direction. This skyrmion Hall angle is predicted to be skyrmion diameter dependent. In contrast, our experimental study finds that the skyrmion Hall angle is diameter independent for skyrmions with diameters ranging from 35 to 825 nm. At an average velocity of 6 ± 1 ms−1, the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local magnetic configuration

Enhancement of perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction in thin ferromagnetic films by atomic-scale modulation of interfaces

To stabilize nontrivial spin textures, e.g., skyrmions or chiral domain walls in ultrathin magnetic films, an additional degree of freedom, such as the interfacial Dzyaloshinskii–Moriya interaction (IDMI), must be induced by the strong spin-orbit coupling (SOC) of a stacked heavy metal layer. However, advanced approaches to simultaneously control the IDMI and perpendicular magnetic anisotropy (PMA) are needed for future spin-orbitronic device implementations. Here, we show the effect of atomic-scale surface modulation on the magnetic properties and IDMI in ultrathin films composed of 5d heavy metal/ferromagnet/4d(5d) heavy metal or oxide interfaces, such as Pt/CoFeSiB/Ru, Pt/CoFeSiB/Ta, and Pt/CoFeSiB/MgO. The maximum IDMI value corresponds to the correlated roughness of the bottom and top interfaces of the ferromagnetic layer. The proposed approach for significant enhancement of PMA and the IDMI through interface roughness engineering at the atomic scale offers a powerful tool for the development of spin-orbitronic devices with precise and reliable controllability of their functionality