Yttrium Iron Garnet Films Research Articles

Static and Dynamic Magnetic Properties of Single‐Crystalline Yttrium Iron Garnet Films Epitaxially Grown on Three Garnet Substrates

AbstractSingle‐crystalline yttrium iron garnet (YIG) films are grown on gadolinium gallium garnet (GGG), rare‐earth‐substituted GGG, and neodymium gallium garnet (NGG) substrates, and their crystalline structures, surface morphologies, magnetic and magneto‐optical properties, spin wave (SW) spectra of the forward volume (FV) mode, and damping parameters are characterized. YIG grown on NGG shows the smallest out‐of‐plane effective anisotropy field of 1080 Oe among the three samples because of its larger magnetoelastic anisotropy contribution, and its damping parameter is 1.1 × 10−3. The FV SW dispersion curve is calculated from the magnetic anisotropy and it shows good agreement with experimental data.

Tens of micron-thick, crack-free yttrium iron garnet films on a Gd3Ga5O12 substrate based on the layer by layer growth method

In this paper, the maximum thickness of crack-free yttrium-iron-garnet ferrite film was increased from 7 to 13 µm by layer by layer growth method. Also, the effect of a layer by layer growth method on films morphology, crystal structure and magnetic properties were investigated. X-ray diffraction θ–2θ revealed the orientation of crystal structure could be increased by the layer-by-layer growth method. Scanning electron microscopy and stylus profiler measurement showed the roughness and morphology of film surface were improved efficiently after using the layer-by-layer growth method. Magnetic hysteresis loops and FMR spectrum representing this layer-by-layer growth method could efficiently increase film magnetism and decrease FMR linewidth. Consequently, this innovative method of layer-by-layer growth efficiently provides a pathway to prepare excellent properties, tens of micron-thick, crack-free yttrium iron garnet films and creates unique significance in the electronics industry.

Measurement of Birefringence Using the Magneto-Optical Modulator in the Magnetomechanical Resonance Mode

In order to detect magnetic linear birefringence of new materials, we have developed an installation using the magneto-optical modulator in the mode of magnetomechanical resonance. We have theoretically substantiated and experimentally applied radiation with phase-frequency dependencies of the Stokes vector on magnetomechanical resonance frequency for measuring magnetic linear birefringence. Our results demonstrate that the radiation in which the variable components of the Stokes vector have different initial phases after passing through the sample with linear birefringence leads to additional phase delays of the signal at the output of the photopolarimeter. As an example, the results of measurements of the magnetic linear birefringence in the film of yttrium iron garnet have been introduced. The minimum value of the linear birefringence which was measured in this experiment 0.018 deg. The advantage of the installation is the independence of the measurements results from the changes of the intensity in the optical system.

Electric field tuning of magnetism in heterostructure of yttrium iron garnet film/lead magnesium niobate-lead zirconate titanate ceramic

In this paper, the converse magnetoelectric (CME) effect by electric field tuning of magnetization in an original heterostructure composed of a polycrystalline yttrium iron garnet (YIG) film and a lead magnesium niobate-lead zirconate titanate (PMN-PZT) ceramic is presented. The magnetic performances of the YIG films with different thicknesses under a DC electric field applied to the PMN-PZT ceramics and a bias magnetic field are investigated. All the magnetization-electric field curves are found to be in good agreement with the butterfly like strain curve of the PMN-PZT ceramic. Both the sharp deformation of about 2.5‰ of PMN-PZT and the easy magnetization switching of YIG are proposed to be the reasons for the strongest CME interaction in the composite at the small electric coercive field of PMN-PZT (4.1 kV/cm) and the small magnetic coercive field of YIG (20 Oe) where the magnetic susceptibility reaches its maximum value. A remarkable CME coefficient of 3.1 × 10−7 s/m is obtained in the system with a 600 nm-thick YIG film. This heterostructure combining multiferroics and partially magnetized ferrite concepts is able to operate under a small or even in the absence of an external bias magnetic field and is more compact and power efficient than the traditional magnetoelectric devices.

Exchange-torque-induced excitation of perpendicular standing spin waves in nanometer-thick YIG films

Spin waves in ferrimagnetic yttrium iron garnet (YIG) films with ultralow magnetic damping are relevant for magnon-based spintronics and low-power wave-like computing. The excitation frequency of spin waves in YIG is rather low in weak external magnetic fields because of its small saturation magnetization, which limits the potential of YIG films for high-frequency applications. Here, we demonstrate how exchange-coupling to a CoFeB film enables efficient excitation of high-frequency perpendicular standing spin waves (PSSWs) in nanometer-thick (80 nm and 295 nm) YIG films using uniform microwave magnetic fields. In the 295-nm-thick YIG film, we measure intense PSSW modes up to 10th order. Strong hybridization between the PSSW modes and the ferromagnetic resonance mode of CoFeB leads to characteristic anti-crossing behavior in broadband spin-wave spectra. We explain the excitation of PSSWs by exchange coupling between forced magnetization precessions in the YIG and CoFeB layers. If the amplitudes of these precessions are different, a dynamic exchange torque is generated, causing the emission of spin waves from the interface. PSSWs form when the wave vector of the spin waves matches a perpendicular confinement condition. PSSWs are not excited if exchange coupling between YIG and CoFeB is eliminated by a 10 nm Ta spacer layer. Micromagnetic simulations confirm the exchange-torque-driven mechanism.

Detecting the phonon spin in magnon–phonon conversion experiments

Recent advances in the emerging field of magnon spintronics have stimulated renewed interest in phenomena involving the interaction between spin waves, the collective excitations of spins in magnetic materials that quantize as magnons, and the elastic waves that arise from excitations in the crystal lattice, which quantize as phonons. In magnetic insulators, owing to the magnetostrictive properties of materials, spin waves can become strongly coupled to elastic waves, forming magnetoelastic waves—a hybridized magnon–phonon excitation. While several aspects of this interaction have been subject to recent scrutiny, it remains unclear whether or not phonons can carry spin. Here we report experiments on a film of the ferrimagnetic insulator yttrium iron garnet under a non-uniform magnetic field demonstrating the conversion of coherent magnons generated by a microwave field into phonons that have spin. While it is well established that photons in circularly polarized light carry a spin, the spin of phonons has had little attention in the literature. By means of wavevector-resolved Brillouin light-scattering measurements, we show that the magnon–phonon conversion occurs with constant energy and varying linear momentum, and that the light scattered by the phonons is circularly polarized, thus demonstrating that the phonons have spin. Experiments on a magnetostrictive material reveal the conversion between coherent magnons and phonons that have spin.

Measurements of long-wavelength spin waves for the magnetic field in the Damon-Eshbach, backward-volume and forward-volume geometries of an yttrium iron garnet film

We report systematic measurements of the dispersion of long wavelength spin waves for a wide range of wave vectors for the magnetic field along the three principal directions defining the forward volume, backward volume and Damon-Eshbach modes of a 9.72 μm thick film of an yttrium iron garnet obtained using lithographically patterned, multi-element, spatially resonant, antennas. Overall good agreement is found between the experimental data for the backward volume and Damon-Eshbach modes and the magnetostatic theory of Damon and Eshbach. Also, good agreement is found between the experimental data for the forward volume mode and the theory of Damon and van de Vaart.

Observation of spin superfluidity: YIG magnetic films and beyond

From topology of the order parameter of the magnon condensate observed in yttrium-iron-garnet (YIG) magnetic films one must not expect energetic barriers making spin supercurrents metastable. But we show that some barriers of dynamical origin are possible nevertheless until the gradient of the phase (angle of spin precession) does not exceed the critical value (analog of the Landau critical velocity in superfluids). On the other hand, recently published claims of experimental detection of spin superfluidity in YIG films and antiferromagnets are not justified, and spin superfluidity in magnetically ordered solids has not yet been experimentally confirmed.

Nonlinear spin conductance of yttrium iron garnet thin films driven by large spin-orbit torque

We report a study on spin conductance in ultra-thin films of Yttrium Iron Garnet (YIG), where spin transport is provided by propagating spin waves, that are generated and detected by direct and inverse spin Hall effects in two Pt wires deposited on top. While at low current the spin conductance is dominated by transport of thermal magnons, at high current, the spin conductance is dominated by low-damping non-equilibrium magnons thermalized near the spectral bottom by magnon-magnon interaction, with consequent a sensitivity to the applied magnetic field and a longer decay length. This picture is supported by microfocus Brillouin Light Scattering spectroscopy.

Electrical properties of epitaxial yttrium iron garnet ultrathin films at high temperatures

We report a study on the electrical properties of 19-nm-thick yttrium iron garnet (YIG) films grown by liquid phase epitaxy on gadolinium gallium garnet single crystal. The electrical conductivity and Hall coefficient are measured in the high-temperature range [300,400] K using a Van der Pauw four-point probe technique. We find that the electrical resistivity decreases exponentially with increasing temperature following an activated behavior corresponding to a band gap of ${E}_{g}\ensuremath{\approx}2$ eV. It drops to values about $5\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{4pt}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\text{cm}$ at $T=400$ K, thus indicating that epitaxial YIG ultrathin films behave as large gap semiconductors. We also infer the Hall mobility, which is found to be positive ($p$ type) at 5 ${\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{sec}}^{\ensuremath{-}1}$ and almost independent of temperature. We discuss the consequence for nonlocal spin transport experiments performed on YIG at room temperature and demonstrate the existence of electrical offset voltages to be disentangled from pure spin effects.

Propagation of magnetostatic spin waves in an yttrium iron garnet film for out-of-plane magnetic fields

We have observed the propagation of spin waves across a thin yttrium iron garnet film on (1 1 1) gadolinium gallium garnet for magnetic fields inclined with respect to the film plane. Two principle planes were studied: that for H in the plane defined by the wave vector k and the plane normal, n, with limiting forms corresponding to the Backward Volume and Forward Volume modes, and that for H in the plane perpendicular to k, with limiting forms corresponding to the Damon-Eshbach and Forward Volume modes. By exciting the wave at one edge of the film and observing the field dependence of the phase of the received signal at the opposing edge we determined the frequency vs. wavevector relation, ω = ω (k), of various propagating modes in the film. Avoided crossings are observed in the Damon-Eshbach and Forward Volume regimes when the propagating mode intersects the higher, exchange split, volume modes, leading to an extinction of the propagating mode; analysis of the resulting behavior allows a determination of the exchange parameter. The experimental results are compared with theoretical simulations.

Combining the sol gel method and spin coating to obtain YIG films with low FMR linewidth on silicon (100) substrate

Combining the sol gel method and spin coating technique, yttrium iron garnet (YIG) films were obtained on silicon (Si) substrate. Four YIG films with different thicknesses were fabricated to achieve low FMR linewidth. The x-ray diffraction has shown a single phase, belonging to the cubic structure of the YIG, while the morphology of the films has presented small pores and some grains on the surface. The FMR linewidth of the YIG films decreased 110 Oe, 108 Oe, 93 Oe and 71 Oe as the film thickness increased 134 nm, 246 nm, 376 nm and 489 nm, respectively. This result indicates that high-quality YIG films can be achieved on Si substrates, controlling the thickness. The sol gel method is shown as a very economical and easy alternative to obtain YIG films with low FMR linewidth, which may be important for making microwave integrated devices.

Evidence for the role of the magnon energy relaxation length in the spin Seebeck effect

Temperature-dependent spin Seebeck effect data on Pt|yttrium iron garnet (YIG) (${\mathrm{Y}}_{3}\mathrm{F}{\mathrm{e}}_{5}{\mathrm{O}}_{12}$)|gallium gadolinium garnet ($\mathrm{G}{\mathrm{d}}_{3}\mathrm{G}{\mathrm{a}}_{5}{\mathrm{O}}_{12}$) are reported for YIG films of various thicknesses. The effect is reported as a spin Seebeck resistivity (SSR), the inverse spin-Hall field divided by the heat flux, to circumvent uncertainties about temperature gradients inside the films. The SSR is a nonmonotonic function of YIG thickness. A diffusive model for magnon transport demonstrates how these data give evidence for the existence of two distinct length scales in thermal spin transport, a spin-diffusion length, and a magnon energy relaxation length.

Strong excitation of surface and bulk spin waves in yttrium iron garnet placed in a split ring resonator

This paper presents an experimental study of the inverse spin Hall effect (ISHE) in a bilayer consisting of a yttrium iron garnet (YIG) and platinum (Pt) loaded on a metamaterial split ring resonator (SRR). The system is excited by a microstrip feed line which generates both surface and bulk spin waves in the YIG. The spin waves subsequently undergo spin pumping from the YIG film to an adjacent Pt layer, and is converted into a charge current via the ISHE. It is found that the presence of the SRR causes a significant enhancement of the mangetic field near the resonance frequency of the SRR, resulting in a significant increase in the ISHE signal. Furthermore, the type of spin wave generated in the system can be controlled by changing the external applied magnetic field angle (). When the external applied magnetic field is near parallel to the microstrip line (), magnetostatic surface spin waves are predominantly excited. On the other hand, when the external applied magnetic field is perpendicular to the microstrip line (), backward volume magnetostatic spin waves are predominantly excited. Hence, it can be seen that the SRR structure is a promising method of achieving spin-charge conversion, which has many advantages over a coaxial probe.

Thermal dependence of the lateral shift of a light beam reflected from a liquid crystal cell deposited on a magnetic film

We study the influence of the thermo-optic effect and of thermal expansion on the lateral shift experienced by a Gaussian near-infrared beam upon reflection from a voltage-controlled nematic liquid crystal cell deposited on a magnetic yttrium-iron garnet film. Variations of temperature are considered in the range between room temperature and the nematic-isotropic phase transition temperature of the liquid crystal and induce changes in both the layer thicknesses and the permittivity tensor components of the constituents. We show that for all polarization configurations of the incoming and reflected beams, these changes modify the amplitude of the extrema of the lateral beam shift and their position with respect to the incidence angle of the beam and, except in the s–s polarization configuration, to the voltage applied to the liquid crystal cell. In the p–p and p–s polarization configurations, this drift can thus be controlled at some incidence angles by tuning the applied voltage. Moreover, in the p–s configuration, the lateral shift can be also controlled by a magnetization reversal in the magnetic layer. Finally, we discuss the possibility of temperature monitoring using the temperature dependence of the lateral shift in this system.

Effects of an adjacent metal surface on spin wave propagation

We experimentally investigate and model the effects of a copper surface adjacent to a surface on which spin waves propagate in a thin film of yttrium iron garnet (YIG). Investigation was performed using a phase detection method, which can map out the spin wave velocity as a function wavevector for small wavevector with high resolution. This velocity is in good agreement with a simple model and allows for extraction of the separation between the YIG film and the copper.

Temperature Dependence of Magnetic Properties of a Ultrathin Yttrium-Iron Garnet Film Grown by Liquid Phase Epitaxy: Effect of a Pt Overlayer

Liquid phase epitaxy of an 18 nm thick yttrium-iron garnet (YIG) film is achieved. Its magnetic properties are investigated in the 100–400 K temperature range, as well as the influence of a 3 nm thick Pt overlayer on them. The saturation magnetization and the magnetocrystalline cubic anisotropy of the bare YIG film behave similarly to bulk YIG. A damping parameter of only a few $10^{-4}$ is measured, together with a low inhomogeneous contribution to the ferromagnetic resonance linewidth. The magnetic relaxation increases upon decreasing temperature, which can be partly ascribed to impurity relaxation mechanisms. While it does not change its cubic anisotropy, the Pt capping strongly affects the uniaxial perpendicular anisotropy of the YIG film, in particular at low temperatures. The interfacial coupling in the YIG/Pt heterostructure is also revealed by an increase of the linewidth, which substantially grows by lowering the temperature.

Автогенерация хаотического СВЧ-сигнала в спин-волновом оптоэлектронном генераторе

Abstract —The self-generation of a chaotic microwave signal in a spin-wave optoelectronic generator has been experimentally investigated for the first time. The generator was a ring circuit, in the microwave path of which there was a spin-wave delay line on the film of an yttrium iron garnet (YIG) and a microwave amplifier. The optical path contained a fiber optic delay line. The nonlinear element of the generator was a film of YIG, which worked under the conditions of four-wave parametric interaction of spin waves. It has been shown that it is possible to generate monochromatic, periodic, quasi-periodic, and chaotic microwave signals by controlling the gain coefficient of the ring. The parameters characterizing the chaotic signal that are generated by the ring have been determined.

Фильтрация поверхностных магнитостатических волн в пленках железо-иттриевого граната переменной ширины при возбуждении фокусирующими преобразователями

AbstractWe have studied the filtration of surface spin waves in yttrium iron garnet (YIG) films of variable width excited by focusing transducers integrated with the film.

Effect of lattice mismatch stress on magnetic domain of epitaxial single crystal (BiTm)3(GaFe)5O12 film

Yttrium iron garnet (YIG) film is a kind of magnetic film and has been investigated extensively because of its excellent magnetic properties and various applications in different fields. Generally, the easy-axis of the film is in-plane and can be changed from in-plane to out-of-plane by introducing some Bi3+ ions into the dodecahedral sites as it has big uniaxial anisotropy, which will be very important in magnetic bubble memories, magneto-optical devices and the new development of spin-wave logic devices. In comparison with many other preparation techniques, the liquid phase epitaxy (LPE) has been consider as a potential method of realizing perpendicular magnetization film due to its big growth-induced anisotropy. However, the LPE technique has more stringent requirements for lattice match between garnet film and gadolinium gallium garnet (GGG) substrate, especially in the growth of thick film. The lattice match is the key factor in LPE growth if the aim of experiment is to achieve a perfect quality and thick film. In most of experiments, there always exists the lattice mismatch between the film and substrate. Owing to the film and substrate have different chemical compositions, their lattice mismatch stress is unavoidable. The purpose of this paper is to investigate the effect of the stress on the anisotropy and then the magnetic domain of (BiTm)3(GaFe)5O12 single crystal film. In our experiment, the monocrystalline (BiTm)3(GaFe)5O12 films are prepared on (111)-oriented GGG substrates by LPE technique and the effect of lattice mismatch stress on the uniaxial anisotropy and magnetic domain are investigated. It is found that the lattice constant of the film is mainly determined by the content of Bi3+ in the film composition. and the increase of Bi3+ content leads to the increase of the film lattice constant, which affects the lattice mismatch stress between film and substrate. The lattice mismatch stress can adjust the perpendicular anisotropy of film which is the main reason for the domain changes. As the mismatch stress changes from tensile stress to compressive stress gradually, the magnetic bubble domain is transformed first into maze domain, and then into the partially striped domain, finally into the completely striped domain. The mismatch tensile stress is an effective method to enhance perpendicular anisotropy, when the growth-induced perpendicular anisotropy is not large enough. The bubble domain can only appear on the film with large tensile stress. The domain size is closely related to the stress. The domain width becomes wider as the mismatch stress becomes larger and it has the smallest domain size as the stress is minimum. These experimental results are very useful in controlling the uniaxial anisotropy and magnetic domain based on the change of the lattice mismatch stress in the growth process.