R. Gieniusz

Single antidot as a passive way to create caustic spin-wave beams in yttrium iron garnet films

Single antidot as a passive point excitation source has been implemented to create caustic spin-wave beams in yttrium iron garnet film. Diffraction of surface magnetostatic spin waves from such antidot is investigated experimentally and theoretically. Our experimental results from Brillouin light scattering spectroscopy indicate that the diffraction beams, which manifest as reflection, extinction, and semicaustic lines, are tunable by the frequency and direction of the incident wave. Numerical calculations are in good agreement with the experimental findings and explain the directions of caustic beams caused by the diffraction.

Resonant frequency multiplication in microscopic magnetic dots

We demonstrate the phenomenon of nonlinear frequency multiplication in sub-micrometer Permalloy dots. The efficiency of multiplication is strongly enhanced when the harmonic is resonant with the normal dynamical modes of the dot. We find that the characteristics of resonant enhancement are dependent on the spatial symmetry of the dynamical mode and are different for the double- and the triple-frequency harmonics. The resonant frequency tripling is particularly efficient, providing a practical route for the implementation of microscopic integrated microwave frequency multipliers.

The effect of magnetostatic coupling on spin configurations in ultrathin multilayers

(Co/Au)N ultrathin multilayers with perpendicular and in-plane magnetic anisotropy were studied experimentally using a combination of ferromagnetic resonance, magneto-optical magnetometry and microscopy (with both in-plane and out-of-plane magnetization-sensitive longitudinal and polar Kerr effects), and magnetic force microscopy (MFM). Three-dimensional magnetization distributions were reconstructed from micromagnetic simulations complemented by the measured magnetic parameters of the multilayers and observations by Kerr microscopy and MFM. It is shown that, in the reorientation phase transition (RPT) zone – the range of anisotropy characterized by 0 < Q < 1 (the ratio of the anisotropy energy to be gained by magnetization along the easy axis perpendicular to the sample surface, and the magnetostatic energy of a uniformly magnetized layer along the surface normal) – the three-dimensional magnetization distributions consist of alternating pairs of vortices and half-antivortices, both with in-plane magneti...

An antidot array as an edge for total non-reflection of spin waves in yttrium iron garnet films

An array of antidots has been used as an edge to create the phenomenon of total non-reflection of spin waves in yttrium iron garnet films. At the critical angle between the line of antidots and the magnetic field, we observe a high-intensity beam of spin waves moving along the line of antidots. The properties of these waves are investigated experimentally by Brillouin light scattering spectroscopy. The conditions required for the occurrence of this phenomenon based on an analysis of the properties of the isofrequency dependencies are presented. The numerical simulations are in good agreement with those of the experimental measurements.

Magnonic band gaps in YIG-based one-dimensional magnonic crystals: An array of grooves versus an array of metallic stripes

We present an experimental and theoretical study of magnonic band gaps in planar one-dimensional magnonic crystals of two types, with a periodic array of metallic stripes or a periodic array of grooves on an yttrium iron garnet film. Propagating magnetostatic surface spin waves are excited in the considered periodic magnetic structures and measured by microstripe transducers with a vector network analyzer and with a Brillouin light scattering spectroscopy. The properties of magnonic band gaps are explained and illustrated by finite element method calculations. We demonstrate a major influence of the nonreciprocal spin-wave dispersion properties induced by metallic stripes on the width of the magnonic band gap and its dependence on the external magnetic field. The indirect character of the band gap and the higher group velocity of spin waves in the metallic magnonic crystal are identified as the main causes of the wider band gap and steeper decrease in its width with increasing magnetic field in this structure as compared to the grooved magnonic crystal. Potential applications of both types of magnonic crystals and prospects for their miniaturization are discussed as well.

The switching of strong spin wave beams in patterned garnet films

The application of spin waves in communication with information encoded in amplitude and phase could replace or enhance existing microelectronic and microwave devices with significantly decreased energy consumption. Spin waves (SW) are usually transported in a magnetic material shaped to act as a waveguide. However, the implementation of SW transport and switching in plane homogeneous magnetic films and running as a narrow beam with a small divergence angle still present a challenge. We propose a realization of a strong SW switchers based on a patterned yttrium iron garnet (YIG) film that could serve as a magnonic fundamental building block. Our concept relies on the creation of a narrow beam of relatively short-wavelength SW by effect of a total non-reflection, found to be tied to refraction on the decreasing internal magnetic field, near a line of antidots at YIG. Nonreciprocal SW excitation by a microstrip antenna is used for controlling the direction of the signal flow. We demonstrate unique features of the propagation of microwave-excited SW beams, provide insight into their physics and discuss their potential applications in high-frequency devices.

Magnetization reversal mechanism in patterned (square to wave-like) Py antidot lattices

The effects of shape and geometry of antidot (square, bi-component, and wave-like) lattices (ADLs) on the magnetization reversal processes and magnetic anisotropy has been systematically investigated by magneto-optical Kerr effect based microscopy. Our experimental results were reproduced by micromagnetic simulations, which highlight the qualitative agreement with the experimental results. We have demonstrated that a small antidot in the center of a unit cell in the square ADL is sufficient to induce additional easy axes with large coercive fields. In wave-like patterns, narrow channels connecting smaller and larger antidots (bi-component ADL) further drastically change the anisotropy map, creating the high coercive fields along a wide angular range (90°) of directions parallel to the channels. In simulated results, we have observed formation of periodic domain structures in all ADLs, however, in the case of a wave-like pattern it is most regular and moreover two different periodic patterns are stabilized at different applied magnetic field values. The formation of 360° domain walls were also observed in wave-like ADL where these domains are formed along the lines connecting adjacent larger and smaller antidots, perpendicular to the channels. These findings point out the possibility of exploiting ADLs with complex unit cells in magnonic or spintronic applications.

Magnetization Reversal of Disorder-Induced Ferromagnetic Regions in Fe 60 Al 40 Thin Films

Magnetization processes were investigated by employing magnetometry and magnetic domain imaging using magnetooptical longitudinal and polar effects in Fe60Al40 films of 40 nm thickness. The films were initially chemically ordered and weakly ferromagnetic, and a large increase in the saturation magnetization was achieved through chemical disorder induced by Ne+-ion irradiation. Various sample geometries were investigated: 1) continuous film; 2) homogenously irradiated wire; and 3) magnetic stripe-patterned wire. Magnetization reversal and magnetic domains formed under the influence of the above sample geometries are reported.

Evolution of magnetic domain structure formed by ion-irradiation of B2-Fe 0.6 Al 0.4

Magnetic domains and magnetization reversal in 40 nm thick films of Fe0.6Al0.4, have been studied by longitudinal magneto-optical Kerr effect. By varying the Ne(+) ion-energy E between 2 and 30 keV (keeping a constant fluence), we varied the depth-penetration of the ions, and thereby influenced the homogeneity of the induced saturation magnetization M(s). The dependence of coercivity on ion energy shows maximum for 5 keV Ne(+). Considerable differences in the magnetic domain formation and magnetization reversal processes were observed: at low E (≤ 5keV), the reversal process is dominated by domain nucleation mechanism (high density of domain nucleation sites), consistent with the occurrence of an inhomogeneous M(s). Films irradiated with E > 5keV ions exhibit significantly low domain nucleation density, and the reversal is dominated by domain propagation mechanism, suggesting homogeneity in induced M(s). These results demonstrate the tunability of magnetization reversal behavior in materials possessing disorder induced magnetic phase transitions.

Magnetic properties, spin waves and interaction between spin excitations and 2D electrons in interface layer in Y3Fe5O12/AlO x /GaAs-heterostructures

We describe synthesis of submicron Y3Fe5O12 (YIG) films sputtered on GaAs-based substrates and present results of the investigation of ferromagnetic resonance (FMR), spin wave propagation and interaction between spin excitations and 2D electrons in interface layer in YIG / AlOx / GaAs-heterostructures. It is found that the contribution of the relaxation process to the FMR linewidth is about 2 % of the linewidth \Delta H. At the same time, for all samples FMR linewidths are high. Sputtered YIG films have magnetic inhomogeneity, which gives the main contribution to the FMR linewidth. Transistor structures with two-dimensional electron gas (2DEG) channels in AlOx / GaAs interface governed by YIG-film spin excitations are designed. An effective influence of spin excitations on the current flowing through the GaAs 2DEG channel is observed. Light illumination results in essential changes in the FMR spectrum. It is found that an increase of the 2DEG current leads to an inverse effect, which represents essential changes in the FMR spectrum.