Broadened low-field modes in thick yttrium iron garnet epilayers

Damped surface modes in thick YIG epilayers which appear at fields below the Damon-Eshbach limit in microwave spectra with the dc magnetic field parallel to the surface, have been investigated. The introduction of a surface anisotropy term in the boundary conditions of the propagation equations qualitatively accounts for these low-field modes.     

Synthesis of yttrium iron garnet precursor particles by homogeneous precipitation

Yttrium iron garnet (YIG) precursor particles were obtained by homogeneous precipitation in a nitrate salt solution by a reaction involving the thermal decomposition of urea. Chemical analysis indicated that solid phases were initially precipitated with sequential iron ion content. The precipitate formed was an amorphous mixed iron oxide phase. The complex composition and the thermal decomposition of the precipitate were studied by thermogravimetry-differential thermal analysis, differential scanning calorimetry, X-ray diffraction, and Fourier transform-infrared spectroscopy. Precipitate morphology was observed by SEM and TEM. Fine-grained single-phase yttrium iron garnet (YIG:Y₃Fe₅O₁₂) powders were obtained by calcination of the precipitate at 1200 °C. YFeO₃ intermediate compound was formed at 600 °C prior to the final crystallization of YIG.     

Epitaxial iron garnet films with submicron diameter magnetic bubbles

Mixed rare earth iron garnet compositions have been developed in the form of epitaxial films which support submicron diameter magnetic bubbles. Sm_0.75Yb_2.25Fe₅O₁₂, Eu_0.9Yb_2.1Fe₅O₁₂ and Eu_1.2Lu_1.8Fe₅O₁₂ films on (111) Gd₃Ga₅O₁₂ as well as Sm_1.5Yb_1.5Fe₅O₁₂ and Eu_1.7Yb_1.3Fe₅O₁₂ films on (111) Sm₃Ga₅O₁₂ can be grown by an isothermal liquid phase epitaxy method. The effects of growth conditions on film composition and the lattice mismatch between a film and its substrate are discussed.     

Polar and longitudinal magneto-optical spectroscopy of bismuth substituted yttrium iron garnet films grown by pulsed laser deposition

Ferrimagnetic bismuth substituted yttrium iron garnet Bi_xY_3 − xFe₅O₁₂ (BiYIG) films with x = 1 and 2 pulsed laser deposited onto (111) Gd₃Ga₅O₁₂ (GGG) substrates were studied using magneto-optical (MO) Kerr spectroscopy in the photon energy range of 1.8-5 eV at both polar and longitudinal magnetizations. The interference at lower photon energies provided the refined film thicknesses ranging between 70 and 200 nm. The films were grown under compressive strain and displayed saturation magnetizations (μ₀M_s) lower than that of their bulk counterparts due to the presence of nanograins forming BiYIG layers and/or magnetically dead interface layers. The trends in the MO spectra agree with those deduced from the published permittivity tensor data for BiYIG using a transfer matrix model applied to a film (BiYIG)-substrate (GGG) system. Due to the reduced μ₀M_s the predicted amplitudes are typically higher. The agreement was improved using effective medium approach or by incorporating into the model MO passive interface layers. The information on MO activity at longitudinal magnetization in the garnet layers below 100 nm presents interest for MO imaging and magnetophotonic devices. The results suggest that the MO Kerr spectroscopy combined with MO Kerr magnetometry may represent a valuable, cheap and nondestructive tool for the characterization of magnetic garnet films less than 200 nm thick.     

Liquid phase epitaxy growth of bismuth-substituted yttrium iron garnet thin films for magneto-optical applications

The novel Bi-substituted rare-earth iron garnet films were grown by the modified liquid phase epitaxy (LPE) technique for use as a 45° Faraday rotator in optical isolators. First, single crystals of Y₃Fe₅O₁₂ (YIG), with a lattice constant of 1.2378 nm, were grown by means of the Czochralski method. Using the seed crystal of YIG instead of the conventional non-magnetic garnet of Gd₃Ga₅O₁₂ as a substrate, a film of BiYbIG was grown by means of the LPE method from Bi₂O₃–B₂O₃ fluxes. The structural, magnetic and magneto-optical properties of BiYbIG LPE film/YIG crystal composite have been investigated using directional X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and near-infrared transmission spectrometry. The saturation magnetization 4πM_s has been estimated to be approximately 1200 G. The Faraday rotation spectrum was measured by the method of rotating analyzer ellipsometry with the wavelength varying from 800 to 1700 nm. The resultant Bi_0.37Yb_2.63Fe₅O₁₂ LPE film/YIG crystal composite showed an increased Faraday rotation coefficient due to doping Bi³⁺ ions on the dodecahedral sites of the magnetic garnet without increasing absorption loss, therefore a good magneto-optic figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved of 21.5 deg/dB and 30.2 deg/dB at 1300 nm and 1550 nm wavelengths, respectively, at room temperature. Since Yb³⁺ ions and Y³⁺ ions provide the opposite contributes to the wideband and temperature characteristic of Faraday rotation, the values of Faraday rotation wavelength and temperature coefficients were reduced to 0.06%/nm and 0.007 deg/°C at 1550 nm wavelength, respectively.     

Microwave relaxation properties of Be2+-doped yttrium iron garnet LPE films

A series of yttrium iron garnet epitaxial films containing an increasing concentration of beryllium has been grown and studied by the FMR technique in the microwave range. A nearly linear increase of the films line-width with the BeO content in the melt together with high temperature air annealings and reduction treatments in aqueous solutions evidences the presence of Fe⁴⁺ Be²⁺ pairs in the lattice to provide ion charge equilibrium.     

Synthesis of polycrystalline yttrium iron garnet and yttrium aluminium garnet from organic precursors

Polycrystalline Y₃Fe₅O₁₂ (YIG) and Y₃Al₅O₁₂ (YAG) garnets have been prepared by the organic solution technique using a novel organic precursor. The thermal decomposition of the precursor and subsequent formation of the garnet phases was studied by thermal analysis, X-ray diffraction and Fourier transform infra red spectroscopy (FTIR) including diffuse reflectance FTIR (DRIFT). The precursor of YIG decomposes to give the garnet phase as the main component at 800 °C. YFeO₃ and Fe₂O₃ are also present, and react to give YIG at higher temperatures. Single-phase YAG can be obtained from its precursor at 1100 °C. The reaction proceeds via a hexagonal YAlO₃ intermediate which is formed at 850 °C.     

Electromagnetic excitation of ultrasonic oscillations by yttrium iron garnet films on gallium gadolinium garnet substrates

We have studied the phenomenon of contactless excitation of ultrasonic oscillations by thin yttrium iron garnet (YIG) films on gallium gadolinium garnet (GGG) substrates upon application of the superposition of a constant magnetic bias field and alternating magnetic field. Dimensional resonance effects that cannot be explained in the framework of existing theoretical notions have been discovered, in particular, in dependences of the amplitude of excited longitudinal oscillations on the YIG film thickness, frequency of ultrasound, and degree of homogeneity and strength of the magnetic bias field. It is suggested that the observed phenomenon is caused by resonant participation of the intrinsic oscillations of domain walls in the excitation of ultrasound.     

Calcium germanium substituted iron garnet films for magnetic bubble applications

Mixed rare earth iron garnet films containing calcium and germanium have been grown on (111) oriented gadolinium gallium garnet (GGG) substrates. The effect of growth conditions on film composition and properties is discussed. The 5 μm diameter bubble films have good magnetic properties; however, temperature control during film growth is very critical.     

Magnetic and electrical properties of lanthanum substituted yttrium iron garnets

Polycrystalline yttrium lanthanum iron garnets (Y₃La _x Fe_5-x O₁₂) with varying La substitution (0 ≤ x ≤ 0.5) have been prepared in the pellet form, and studied by X-ray diffraction, magnetization, a.c. susceptibility and electrical resistivity measurements. The lattice constants are determined and the applicability of Vegard’s law has been tested. The saturation magnetization (4 πM _S) decreases very slowly almost linearly with increasing x from x = 0.0–0.5 indicating minimal reduction in ferrimagnetism and least magnetic loss. Variation of saturation magnetic moment per formula unit at 300 K with x can be explained satisfactorily assuming the collinear spin-ordering model. The Curie temperature (T _c) reduces very slowly with increasing x, which is consistent with the observed decrease in 4 πM _S with x. The activation energy (E) decreases very slowly with increasing x for x > 0.1.     

Selective growth of yttrium iron garnet and yttrium ferrite by combinatorial pulsed-laser ablation of common precursors

In this paper, we demonstrate the capability of growing two alternative complex oxides with different stoichiometries and crystal structures, by choosing the appropriate substrate and adjusting the target ablation ratio, and tuning their composition and properties by combinatorial pulsed-laser ablation of their precursors. In particular, we successfully grew epitaxial crystalline yttrium iron garnet (Y₃Fe₅O₁₂) on yttrium aluminium garnet (Y₃Al₅O₁₂) substrates and polycrystalline yttrium ferrite (YFeO₃) on sapphire (α-Al₂O₃) substrates by co-ablation of yttrium oxide and iron oxide targets.     

Tunable magnetostatic waves bandpass filters with scandium doped yttrium iron garnet films

This paper reports results of theoretical and experimental studies of microwave bandpass tuned filters based on magnetostatic surface wave (MSSW) propagation in yttrium iron garnet (YIG) films. Filter transmission and input impedance characteristics for saturation magnetization 139 kAm^–1 of YIG films and 32 kAm^–1 of scandium-doped YIG films have been calculated and measured experimentally. Structures of a planar, multilayer metal-dielectric-YIG geometry are used to model the filters. Parameters of the structures have been optimized with the help of a computer. Scandium-doped YIG films of thickness near 100 m and saturation magnetization 32 kAm^–1 have been found potentially useful in the manufacture of tunable bandpass filters.     

Stochastic generation accompanying parametric excitation of spin waves in yttrium iron garnet films

We report the results of experimental investigations of chaotic self-modulation of the envelope of surface spin waves as a result of first-order spin-wave parametric instability. The experimental apparatus consisted of a microwave oscillator with a spin-wave delay line in the feedback circuit. Pis’ma Zh. Tekh. Fiz. 24, 66–72 (April 12, 1998)     

Dielectric properties and electrical conduction in yttrium iron garnet (YIG)

The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y₃Fe₅O₁₂) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.     

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

Technical Physics Letters - A new type of f lux-gate vector magnetometer based on epitaxial yttrium iron garnet films has been developed and constructed for magnetocardiography (MCG)...     

Open die hot pressing of yttrium iron garnet

A relatively simple and more economical process of open die hot pressing has been employed in preparing high density yttrium iron garnet samples of fine grain size (～ 1–2 μM). The samples have been investigated for the microstructure dependent spinwave line-width (ΔH_k) and FMR line-width (ΔH). The values of ΔH_k and ΔH are in fair agreement with the samples having the same grain size but prepared by the conventional hot pressing using refractory dies.     

Reaction between lead zirconate titanate and yttrium iron garnet

High-temperature sintering of lead zirconate titanate (PZT) + yttrium iron garnet mixtures is accompanied by the formation of cubic yttria-stabilized zirconia. Quantitative phase analysis indicates that PZT loses at least 90% of the ZrO₂. This leads to appreciable changes in the composition of the constituent phases and has an adverse effect on the ME performance of the composite     

The magnetic and dielectric properties of microwave sintered yttrium iron garnet (YIG)

Yttrium iron garnet (YIG) material is widely used in microwave devices. Experiments show that microwave sintering (MS) treated YIG materials possess excellent properties with a saturation magnetization of 14.60 emu/g and coercive force 34.82 Oe. In the frequency range of 1 MHz–1.8 GHz, the relative dielectric constant is from 6.5 to 7.0, the line-width is 105 Oe, dielectric loss less than 0.09 and magnetic loss less than 0.7. Furthermore, the sintering time and temperature were significantly reduced from 20 h and 1300 °C for the conventional sintering (CS) process to 2 h and 900 °C for MS technique, respectively.