Epitaxial Yttrium Iron Garnet Films Research Articles

Patterning Magnonic Structures via Laser Induced Crystallization of Yittrium Iron Garnet

AbstractThe fabrication and integration of high‐quality structures of Yttrium Iron Garnet (YIG) is critical for magnonics. Films with excellent properties are obtained only on single crystal Gadolinium Gallium Garnet (GGG) substrates using high‐temperature processes. The subsequent realization of magnonic structures via lithography and etching is not straightforward as it requires a tight control of the edge roughness, to avoid magnon scattering, and planarization in case of multilayer devices. In this work a different approach is described based on local laser annealing of amorphous YIG films, avoiding the need for subjecting the entire sample to high thermal budgets and for physical etching. Starting from amorphous and paramagnetic YIG films grown by pulsed laser deposition at room temperature on GGG, a 405 nm laser is used for patterning arbitrary shaped ferrimagnetic structures by local crystallization. In thick films (160 nm) the laser induced surface corrugation prevents the propagation of spin‐wave modes in patterned conduits. For thinner films (80 nm) coherent propagation is observed in 1.2 µm wide conduits displaying an attenuation length of 5 µm that is compatible with a damping coefficient of ≈5 × 10−3. Possible routes to achieve damping coefficients compatible with state‐of‐the art epitaxial YIG films are discussed.

Propagating spin-wave spectroscopy in a liquid-phase epitaxial nanometer-thick YIG film at millikelvin temperatures

Performing propagating spin-wave spectroscopy of thin films at millikelvin temperatures is the next step toward the realization of large-scale integrated magnonic circuits for quantum applications. Here, we demonstrate spin-wave propagation in a 100 nm-thick yttrium-iron-garnet (YIG) film at temperatures down to 45 mK, using stripline nanoantennas deposited on YIG surface for electrical excitation and detection. The clear transmission characteristics over the distance of 10 μ m are measured and the extracted spin-wave group velocity and the YIG saturation magnetization agree well with the theoretical values. We show that the gadolinium-gallium-garnet (GGG) substrate influences the spin-wave propagation characteristics only for the applied magnetic fields beyond 75 mT, originating from a GGG magnetization up to 62 kA / m at 45 mK. Our results show that the developed fabrication and measurement methodologies enable the realization of integrated magnonic quantum nanotechnologies at millikelvin temperatures.

Spin-wave diagnostics of epitaxial ferrite-dielectric structures

Purpose of this study is to elucidate the mechanism of transformation of electromagnetic and exchange spin waves (ESW) in a thin transition layer of epitaxial ferrite–dielectric structures, as well as to investigate the possibilities of using short-wave ESW to diagnose magnetic inhomogeneities of epitaxial yttrium-iron garnet (YIG) films. Methods. In this paper, we study the hybridization processes of electromagnetic and exchange spin waves that occur in the transition layer of the YIG film. The features of the dispersion of coupled waves in the vicinity of phase synchronism frequencies under normal and tangential magnetization of the YIG film are investigated. Results. It is shown that within of the thickness transition layer, the dispersion of the excited ESW experiences significant distortions, which manifests itself in frequency shifts of the spin-wave resonance. Based on this, a method for calculating the distribution of spontaneous magnetization over the thickness of the YIG film was proposed, which was used to simulate the processes of excitation of spin-wave resonances. Conclusion. The proposed technique of spin-wave diagnostics of YIG films can be effectively used for non-destructive testing of all types of epitaxial ferrite-dielectric structures, which may be in demand in the field of production and in the field of their practical application.

Spin-wave resonances in a diffusion-sensitive epitaxial film YIG

It is shown that in a tangentially magnetized film of iron yttrium garnet exist two types of resonances --- a homogeneous ferrimagnetic resonance in the region of the film's homogeneous magnetization (outside the diffusion layer), and inhomogeneous spin-wave resonance within the thickness of the diffusion layer. A method of calculating the magnetization distribution over the film thickness using measured frequencies of the spin-wave and ferrimagnetic resonances. The method of mathematical modeling has established that the magnetic inhomogeneity of the transition layer layer introduces significant distortions of the oscillation epure at the frequency of the spin-wave resonance, and the nature of the distortions significantly depends on the magnitude of the magnetizing field. The results of the conducted can be useful for nondestructive control of the layered structure of YIG epitaxial films. Keywords: yttrium iron garnet epitaxial films, exchange spin waves, spinwave electronics, magnonics.

Thickness dependences of the dynamic magnetic properties of epitaxial YIG films prepared by a metal–organic decomposition method

Epitaxial yttrium-iron garnet (YIG) films with various thicknesses were fabricated on gadolinium-gallium garnet substrates by a metal–organic decomposition (MOD) method, and their dynamic and static magnetic properties were investigated. We varied the thickness of the YIG films by repeating spin-coating of the MOD solution and pre-annealing. The lattice constant and the crystal size of the YIG films were almost independent of the thickness (the coating count N). The damping factor and coercive field increased with N. Moreover, the saturation magnetization MS measured using a vibrating sample magnetometer increased with N, although that measured by ferromagnetic resonance was almost independent of N. Thus, both dynamic and static magnetic properties for the YIG films obviously degraded with increasing N. Judging from these results, the repetition of the coating process generates other ferromagnetic micro-crystalline phases at grain boundaries, for instance, γ-Fe2O3 and Fe3O4, which could cause degradation of the magnetic properties of the YIG films prepared by the MOD method.

Magnetism and site occupancy in epitaxial Y-rich yttrium iron garnet films

Y-rich yttrium iron garnet (Y-YIG) thin films were grown on gadolinium gallium garnet substrates using pulsed laser deposition from a ${\mathrm{YFeO}}_{3}$ target. The films are epitaxial on the substrate, and the unit cell of (001)- and (111)-oriented Y-YIG undergoes a tetragonal or rhombohedral distortion, respectively. The Y-YIG has lower room temperature magnetization but higher low-temperature magnetization than bulk YIG, and its Curie temperature was in the range of 330--400 K, depending on the growth conditions. First-principles calculations predict that ${\mathrm{Y}}_{\mathrm{Fe}}$ antisite defects are more stable in octahedral than tetrahedral Fe sites. Temperature-dependent magnetization measurements together with a superexchange dilution model and composition determined from x-ray photoelectron spectroscopy indicate that nonmagnetic species (${\mathrm{Y}}^{3+}$ and vacancies) are predominantly accommodated in the octahedral sites, but there is a significant occupancy of tetrahedral sites.

Ferromagnetic Resonance and Elastic Vibrations in Epitaxial Yttrium Iron Garnet Films

The ferromagnetic resonance (FMR) spectra of epitaxial yttrium iron garnet films are experimentally studied. The field dependences of the FR frequency are used to determine the effective fields induced by the first and second anisotropy constants and the effective uniaxial anisotropy field. The FMR frequency and linewidth are found to increase in the fields lower than 8 Oe applied in the bismuth-containing film plane. This increase is related to the formation of a nonuniform magnetization distribution, which is supported by a direct magnetooptical observation. The FMR spectra are found to be modulated by a set of narrow lines, the amplitude of which is proportional to the FMR signal intensity. The frequency position of the lines is independent of the magnitude and direction of a dc magnetic field. This modulation is shown to be associated with the resonance excitation of transverse elastic vibration modes. The effective magnetoelastic coupling parameter and the linewidth of the elastic vibrations excited by resonance pumping are estimated.

Ferromagnetism in the Ferromagnetic Yttrium Iron Garnet Film/Ferromagnetic Intermetallic Compound Heterostructure

We report on the investigations of the magnetic properties and ferromagnetic resonance in the heterostructure consisting of an epitaxial yttrium iron garnet (Y3Fe5O12) film and a nanometer rare-earth intermetallic superlattice comprised of the (TbCo2/FeCo)n exchange-coupled layers. The (TbCo2/FeCo)n superlattice exhibits the giant magnetostriction and the controlled magnetic anisotropy induced by a magnetic field or elastic stresses. The magnetic interaction of the films in the (TbCo2/FeCo)n/Y3Fe5O12 heterostructure has been experimentally established and the spin current flowing through their interface has been detected.

Exchange spin waves and their application for diagnostics of the layered structure of epitaxial YIG films

The results of modelling of the excitation and propagation processes of exchange spin waves (ESW) in epitaxial films of yttrium iron garnet (YIG) are presented. It is shown that the origin of the efficient ESW excitation is magnetic inhomogeneity, which is always present in a thin transition layer at the interface between a magnetic film and a nonmagnetic substrate. It is found that the parameters of magnetic inhomogeneity significantly affect wave characteristics of the emitted ESWs. A method was proposed for employing ESWs to measure the magnetization distribution parameters over the thickness of the YIG film and the ESW dissipation parameter. The measured parameters were used to calculate the dispersion and attenuation of the ESWs, define their amplitude characteristics in continuous and pulsed regimes, and estimate their phase losses. It is shown that dissipative losses of ESWs are not significant. More significant losses can occur due to phase dispersion on non-parallel reflective surfaces of the YIG film. It is demonstrated that such phase losses can be significantly reduced by precision optical polishing of the YIG film samples.

Ферромагнетизм в гетероструктуре ферромагнитная пленка железо-иттриевого граната/ферромагнитный интерметаллид

Abstract We report on the investigations of the magnetic properties and ferromagnetic resonance in the heterostructure consisting of an epitaxial yttrium iron garnet (Y_3Fe_5O_12) film and a nanometer rare-earth intermetallic superlattice comprised of the (TbCo_2/FeCo)_ n exchange-coupled layers. The (TbCo_2/FeCo)_ n superlattice exhibits the giant magnetostriction and the controlled magnetic anisotropy induced by a magnetic field or elastic stresses. The magnetic interaction of the films in the (TbCo_2/FeCo)_ n /Y_3Fe_5O_12 heterostructure has been experimentally established and the spin current flowing through their interface has been detected.

Spin Waves in YIG-Based Networks: Logic and Signal Processing

An eight-port magnonic network was fabricated from 1 μm thick epitaxial yttrium iron garnet (YIG) film by the photolithography and ion-etching techniques. The network had a form of the 2 × 2 lattice of the 10 μm wide and 100 μm long YIG waveguides with inductive micro-antennas located at the ends and spaced by 90 μm. Effects of the spin waves (SW) propagation and interference in the network were studied experimentally and by micromagnetic simulation. It was shown that one can realize the constructive and destructive interference of the SW at the output transducers by changing the input signals phase. Possibilities to build logic gates and magnetic sensors based on the SW interference was demonstrated.

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Nonreciprocity of backward volume spin wave beams excited by the curved focusing transducer

The focusing effect for spin waves excited by a curved micrometer-sized coplanar waveguide transducer on top of a 5-μm-thick epitaxial yttrium iron garnet film is studied by means of the micro-focused Mandelstam-Brillouin light scattering technique and micromagnetic simulations. The curvilinear transducer is designed to focus the backward volume spin waves on the in-plane bias magnetic field applied along the symmetry axis of the transducer. We show that two-dimensional maps of spin wave intensity exhibit nonreciprocal properties without mirror symmetry with respect to the magnetic field direction and the focusing effect. The observed effects are the consequence of nonreciprocity of the backward volume spin waves travelling at an angle toward the bias field direction.

Solution-Processed Ferrimagnetic Insulator Thin Film for the Microelectronic Spin Seebeck Energy Conversion

The longitudinal spin Seebeck effects with a ferro- or ferrimagnetic insulator provide a new architecture of a thermoelectric device that could significantly improve the energy conversion efficiency. Until now, epitaxial yttrium iron garnet (YIG) films grown on gadolinium gallium garnet (GGG) substrates by a pulsed laser deposition have been most widely used for spin thermoelectric energy conversion studies. In this work, we developed a simple route to obtain a highly uniform solution-processed YIG film and used it for the on-chip microelectronic spin Seebeck characterization. We improved the film roughness down to ∼0.2 nm because the extraction of thermally induced spin voltage relies on the interfacial quality. The on-chip microelectronic device has a dimension of 200 μm long and 20 μm wide. The solution-processed 20 nm thick YIG film with a 10 nm Pt film was used for the spin Seebeck energy converter. For a temperature difference of Δ T ≈ 0.036 K applied on the thin YIG film, the obtained Δ V ≈ 28 μV, which is equivalent to SLSSE ≈ 80.4 nV/K, is close to the typical reported values for thick epitaxial YIG films. The temperature and magnetic field-dependent behaviors of spin Seebeck effects in our YIG films suggest active magnon excitations through the noncoherent precession channel. The effective SSE generation with the solution-processed thin YIG film provides versatile applications of the spin thermoelectric energy conversion.

Chemical solution synthesis and ferromagnetic resonance of epitaxial thin films of yttrium iron garnet

Cubic Yttrium Iron Garnet (YIG) is a technologically important material due to its excellent magneto-optical properties, high electrical resistivity, and a very narrow ferromagnetic resonance, which makes it particularly suitable for applications in filters and resonators at microwave frequencies. These properties depend on the precise stoichiometry and distribution of Fe${}^{3+}$ ions among the octahedral/tetrahedral sites of a complex structure, which required the use of high-vacuum deposition methods for the fabrication of high-quality YIG thin films. In this paper the authors report the synthesis of nanometer-thick epitaxial films of YIG by a simple water-based chemical method. The films show a long spin relaxation time, comparable to that obtained from high-vacuum physical deposition methods. These results demonstrate that chemical methods can compete to develop nanometer-thick YIG films with the quality required for spintronic devices and other high-frequency applications.

A study of magnetic and electronic hyperfine interactions in epitaxial film of yttrium-iron garnet by the method of conversion electron Mössbauer spectroscopy

Magnetic and electric hyperfine interactions in the near-surface layers of epitaxial films of yttrium-iron garnet of the (111) orientation grown by the liquid-phase epitaxy method are studied by the method of the conversion electron Mossbauer spectroscopy (CEMS). The studies reveal a stoichiometric violation of the anion sublattice in the near-surface layers (≈8 × 10–8 m) of yttrium iron garnet film and, as a consequence, the formation of two types of d-sites, which is associated with a significant concentration of point defects in the anion sublattice of the near-surface area and the growing weight of the covalent bonding in the transition film–air layer. This also causes the presence of a fixed doublet component corresponding to iron ions in a paramagnetic state with an intermediate degree of valency between +2 and +3. It is shown that interpretation of the spectroscopic results using the Hamiltonian of mixed magnetic and quadrupole interactions makes it possible to obtain a vector diagram of the spatial orientations of the effective magnetic fields at the Fe57 nuclei and, as a consequence, to reconstruct the formation mechanism of the resulting vector of the magnetic moment of the yttrium iron garnet epitaxial film. Our studies reveal a slight noncollinearity of ≈4° in the orientations of the magnetic moments in the a- and d-sites of iron. The obtained results complement the picture of the magnetic and electronic hyperfine interactions in the epitaxial ferrite-garnet films and should be considered in the practical applications of the magnetic properties of such materials.

Flux-gate magnetic field sensor based on yttrium iron garnet films for magnetocardiography investigations

A new type of f lux-gate vector magnetometer based on epitaxial yttrium iron garnet films has been developed and constructed for magnetocardiography (MCG) investigations. The magnetic field sensor can operate at room temperature and measure MCG signals at a distance of about 1 mm from the thoracic cage. The high sensitivity of the sensor, better than 100 fT/Hz1/2, is demonstrated by the results of MCG measurements on rats. The main MCG pattern details and R-peak on a level of 10 pT are observed without temporal averaging, which allows heart rate anomalies to be studied. The proposed magnetic sensors can be effectively used in MCG investigations.

Spin-wave band-pass filters based on yttrium iron garnet films for tunable microwave photonic oscillators

The paper reports on development of tunable band-pass microwave filters for microwave photonic generators. The filters were fabricated with the use of epitaxial yttrium iron garnet films. Principle of operation of the filters was based on excitation, propagation, and reception of spin waves. In order to obtain narrow pass band, the filtering properties of excitation and reception antennas were exploited. The filters demonstrated insertion losses of 2-3 dB, bandwidth of 25-35 MHz, and tuning range of up to 1.5 GHz in the range 3-7 GHz.

Magnetostatic surface waves in a ferrite–ferromagnetic metal layered medium based on yttrium iron garnet epitaxial films and TbCo2/FeCo nanostructures

The effect of a thin ferromagnetic metal layer placed on the surface of an yttrium iron garnet surface on the spectrum and loss of magnetostatic surface waves (MSSWs) is experimentally investigated in the case of homogeneous metallization and in the case of a system of periodic metal strips. It is shown that essential attenuation is produced by a metal layer whose thickness is substantially smaller than the depth of the skin layer appearing when an MSSW propagates along a ferromagnetic–metal boundary. The presence of the MSSW reflection by the boundary between the metallic and nonmetallic parts of a ferromagnetic film is experimentally confirmed by the Mandelstam–Brillouin spectroscopy.

Pulsed laser deposition of epitaxial yttrium iron garnet films with low Gilbert damping and bulk-like magnetization

Yttrium iron garnet (YIG, Y 3Fe5O12) films have been epitaxially grown on Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) substrates with (100) orientation using pulsed laser deposition. The films were single-phase, epitaxial with the GGG substrate, and the root-mean-square surface roughness varied between 0.14 nm and 0.2 nm. Films with thicknesses ranging from 17 to 200 nm exhibited low coercivity (<2 Oe), near-bulk room temperature saturation moments (∼135 emu cm−3), in-plane easy axis, and damping parameters as low as 2.2 × 10−4. These high quality YIG thin films are useful in the investigation of the origins of novel magnetic phenomena and magnetization dynamics.