Bismuth-substituted Iron Garnet Films Research Articles

Bi-Substituted Ferrite Garnet Type Magneto-Optic Materials Studied at ESRI Nano-Fabrication Laboratories, ECU, Australia

Since 2007, at the Electron Science Research Institute (ESRI) nano-fabrication laboratories, Edith Cowan University, Australia, we have devoted research efforts to the synthesis and characterization of bismuth-containing ferrite-garnet-type thin-film magneto-optic (MO) materials of different compositions. We report on the growth and characteristics of radio frequency (RF) magnetron sputtered bismuth-substituted iron-garnet thin films. We study the process parameters associated with the RF magnetron sputter deposition technique and investigate the results of optimizing process parameters. To achieve the best MO properties, we employ a few unique techniques, such as co-sputtered nanocomposite films and all-garnet multilayer structures, as well as the application of oxygen plasma treatment to amorphous garnet layers immediately following the deposition process. We demonstrated a remarkable enhancement in the MO properties of Bi-containing ferrite-type garnet thin-film materials, including record-high MO figures of merit and improved conventional and unconventional hysteresis loops of Faraday rotation. Previously unpublished research results on the forward-looking applications of magnetic garnet coatings applied to microparticles of advanced luminescent materials are reported. In the context of developing the next-generation ultra-fast optoelectronic devices, such as light intensity switches and modulators, high-speed flat panel displays, and high-sensitivity sensors, it is important to consider the desirable optical, magnetic, and magneto-optic properties that are found in highly bismuth-substituted iron garnet thin-film materials of various composition types.

Magnetoelectric effect and magnetization processes in garnet films

Changes in the domain structure of epitaxial bismuth-substituted iron-garnet films under joint action of AC electric field and DC magnetic field are investigated by the optical polarimetry method. Garnet films exhibit electric field dependent magnetic properties, which have been measured as a function of the applied magnetic field oriented in the plane of the film. The investigations have revealed that the electric field practically does not modify the film magnetization magnitude and the registered magnetoelectric effect is associated with the influence of the electric field on the magnetic anisotropy parameters of the investigated film.

Liquid phase epitaxy growth of (GdYbBi)3(FeGe)5O12 films for magneto-optical applications

As an important component in magneto-optical devices, bismuth-substituted rare-earth iron garnet films play a significant role in guarantying a unidirectional light propagation in optical communication system. In this study, (GdYbBi)3(FeGe)5O12 film with a thickness of 120 μm was successfully grown by liquid phase epitaxy (LPE) technology. Lattice mismatch and internal stress between the epitaxial film and substrates were discussed in detail. Tested results shown that (GdYbBi)3(FeGe)5O12 films exhibit high crystal quality and large specific faraday rotation angle, which indicate that the prepared (GdYbBi)3(FeGe)5O12 films have a great potential to be used in optical communication system.

Enhancement of the spin Seebeck effect owing to bismuth substitution in thermoelectric generators fabricated from LPE Bi-substituted YIG films

Raising the thermoelectric voltage in spin thermoelectric generators is an important subject. We investigated the substitution of bismuth for yttrium to increase spin pumping at the paramagnetic metal and ferrimagnetic insulator (PM/FMI) interface, and tested bismuth-substituted iron garnet films grown by liquid phase epitaxy. Epitaxial Bi-substituted iron garnet films exhibit large growth-induced magnetic anisotropy perpendicular to the film surface. This anisotropy increases the magnetic damping α in the FMI; α also increases with increasing Bi content. We report the rise in voltage observed in a spin thermoelectric generator incorporating Bi-substituted YIG films grown by liquid phase epitaxy, and explain the origin of the voltage rise based on the results of FMR measurements.

Enhanced Magneto-Optic Properties in Sputtered Bi- Containing Ferrite Garnet Thin Films Fabricated Using Oxygen Plasma Treatment and Metal Oxide Protective Layers.

Magneto-optic (MO) imaging and sensing are at present the most developed practical applications of thin-film MO garnet materials. However, in order to improve sensitivity for a range of established and forward-looking applications, the technology and component-related advances are still necessary. These improvements are expected to originate from new material system development. We propose a set of technological modifications for the RF-magnetron sputtering deposition and crystallization annealing of magneto-optic bismuth-substituted iron-garnet films and investigate the improved material properties. Results show that standard crystallization annealing for the as-deposited ultrathin (sputtered 10 nm thick, amorphous phase) films resulted in more than a factor of two loss in the magneto-optical activity of the films in the visible spectral region, compared to the liquid-phase grown epitaxial films. Results also show that an additional 10 nm-thick metal-oxide (Bi2O3) protective layer above the amorphous film results in ~2.7 times increase in the magneto-optical quality of crystallized iron-garnet films. On the other hand, the effects of post-deposition oxygen (O2) plasma treatment on the magneto-optical (MO) properties of Bismuth substituted iron garnet thin film materials are investigated. Results show that in the visible part of the electromagnetic spectrum (at 532 nm), the O2 treated (up to 3 min) garnet films retain higher specific Faraday rotation and figures of merit compared to non-treated garnet films.

Magneto-optical Imaging Using Bismuth-substituted Iron Garnet Films Prepared by Metal–Organic Decomposition

Magneto-optical Imaging Using Bismuth-substituted Iron Garnet Films Prepared by Metal–Organic Decomposition

Magneto-optics of subwavelength all-dielectric gratings.

We provide the experimental research on a novel type of all-dielectric magnetic structure designed to achieve an enhanced magneto-optical response. 1D grating fabricated via etching of bismuth substituted iron garnet film supports the excitation of optical guided modes, which are highly sensitive to the external magnetic field. A unique feature of proposed structure is the synergetic combination of high transparency, tunability, high Q-factor of the resonances and superior magneto-optical response that is two orders higher in magnitude than in the non-structured smooth iron-garnet film. The considered all-dielectric magnetic garnet structures have great potential in various fields including the magneto-optical modulation of light, biosensing and magnetometry.

Faraday rotation in iron garnet films beyond elemental substitutions

In previous decades significant efforts have been devoted to increasing the magneto-optical efficiency of iron garnet materials for the miniaturization of nonreciprocal devices such as isolators and circulators. Elemental substitutions or proper nano-structuring to benefit from optical resonances have been pursued. However, all these approaches still require film thicknesses of at least several tens of microns to deliver useful device applications, and suffer from narrow bandwidths in the case of optical resonance effects. This Letter reports on a newly discovered enhancement of the Faraday Effect observed experimentally in nanoscale bismuth-substituted iron garnet films. It is shown here that this enhancement is not due to elemental substitution or compositional variations. Nor is it due to photon trapping or resonance effects. Comprehensive experimental and theoretical analysis of the Faraday rotation reveals a dramatic seven-fold amplification in the magneto-optic gyrotropy within only 2 nm of the air-surface interface, corresponding to just a couple of atomic monolayers as a result of symmetry-breaking at the air-film interface. This finding opens up an avenue to the application of monolayer magnetic garnets for the control of light.

Magneto-optical imaging plate with backlight for quantitative measurement of magnetic field distribution

We develop a light source, a polarizing film, and a highly bismuth-substituted neodymium iron garnet film which exhibits a large Faraday rotation angle of 11 deg., prepared on a ϕ150 mm diameter glass substrate by the metal–organic decomposition method. To measure the magnetic field distribution quantitatively, the 45° polarizer method was carried out. The magnetic field distribution of a bar magnet was quantitatively measured. Furthermore, we also carried out the polarization modulation method using a white light for quantitative magneto-optical (MO) imaging.

Magnetic properties of bismuth-substituted neodymium iron garnet films on Gd3Ga5O12(100) substrates determined by ferromagnetic resonance measurements

Magnetic properties of Nd3−xBixFe5O12 (0 ≤ x ≤ 3) films prepared by metal organic decomposition on Gd3Ga5O12(100) substrates have been investigated. The Faraday rotation angle θF increased with bismuth concentration. The uniaxial anisotropy constant Ku, cubic magnetocrystalline anisotropy constant K1, gyromagnetic ratio γ, g-factor, and FMR line width ΔH were determined by ferromagnetic resonance measurements. Ku was positive and K1 was negative for all samples. Ku decreased from 9.83 × 104 to 2.05 × 104 erg/cm3 as x increased from 0 to 3. K1 was almost constant irrespective of x, and it took a value between −3.28 × 104 and −2.08 × 104 erg/cm3. γ, g-factor, and ΔH also decreased with increasing bismuth concentration. From the results of the investigation of the in-plane tensile strain applied to the films, the effect of strain on Ku is considered to be small.

Colossal magnetostriction and electrostriction of bismuth-substituted neodymium iron garnet films

Electro- and magnetostriction mechanisms and temperature behavior of the length of bismuth-substituted neodymium iron garnet films on glass and gallium gadolinium garnet have been investigated. Electric- and magnetic-field and temperature dependences of the electro- and magnetostriction constants have been determined. It has been established that the magnetostriction constant changes its sign upon temperature variation. The experimental data are explained using a model of dipole glass with the magnetoelectric and magnetoelastic interaction.

Magneto-optical color imaging of magnetic field distribution

The magneto-optical (MO) imaging technique allows magnetic field distributions to be observed in real-time. In this paper, we demonstrate a MO color imaging technique that allows quantitative values of magnetic fields to be determined by the naked eye. MO color imaging is realized using a MO imaging plate, which contains a bismuth-substituted iron garnet film. The imaging plate was prepared by the metal organic decomposition method, and a light source consisting of green and yellow light-emitting diodes or a white light-emitting diode. MO color imaging of the magnetic field distribution of a commercial ferrite magnet is demonstrated.

Epitaxial Bi–Gd–Sc iron-garnet films for magnetophotonic applications

Novel magneto-optical epitaxial bismuth-substituted iron garnet films of composition (BiGd)3(FeSc)5O12 with large lattice parameter of 12.570 Å have been grown and investigated. Their composition was uniquely chosen to get necessary values of the magnetic and magneto-optical parameters crucial for magneto-optical applications. In particular, the fabricated films have the suppressed cubic magnetic anisotropy (down to 1.2 × 103 erg/cm3) and the large magnetic susceptibility (∼50), due to introducing Sc3+ ions; the diminished saturation magnetization (4πMS ∼ 750 Gs), caused by Gd3+ ions, and relatively large specific Faraday rotation (1.75°/μm, at 655 nm), due to Bi3+ ions. Therefore, the grown magnetic films have record values of the product of the magnetic susceptibility by the Faraday rotation that makes them extremely promising for applications, including magnetometers, magneto-optical visualizers, light modulators and nonreciprocal elements of the integrated optics.

Sensitivity of domain walls of bismuth-substituted iron garnets to a magneto-electric interactions caused by external complex field influence

We revealed the “smearing” effect of domain walls' local areas under conditions with the joint impact of AC and DC electric fields in inhomogeneous magnetic structures of bismuth-substituted iron garnet films. Magneto-optical measurements and the direct visual observations in transmitted light were used for the investigation. The revealed effect depends essentially on the curvature of the domain walls and occurred visually only when an external magnetic field of certain orientation was applied to the sample.

Large magneto-optic enhancement in ultra-thin liquid-phase-epitaxy iron garnet films

Significant departures from bulk-like magneto-optic behavior are found in ultra-thin bismuth-substituted iron-garnet films grown by liquid-phase-epitaxy. These changes are due, at least in part, to geometrical factors and not to departures from bulk-composition in the transient layer at the film-substrate interface. A monotonic increase in specific Faraday rotation with reduced thickness is the signature feature of the observed phenomena. These are traced to size-dependent modifications in the diamagnetic transition processes responsible for the Faraday rotation. These processes correspond to the electronic transitions from singlet 6S ground states to spin-orbit split excited states of the Fe3+ ions in the garnet. A measurable reduction in the corresponding ferrimagnetic resonance linewidths is found, thus pointing to an increase in electronic relaxation times and longer lived excitations at reduced thicknesses. These changes together with a shift in vibrational frequency of the Bi-O bonds in the garnet at reduced thicknesses result in greatly enhanced magneto-optical performance. These studies were conducted on epitaxial monocrystalline Bi0.8Gd0.2Lu2Fe5O12 films.

Microcavity One-Dimensional Magnetophotonic Crystals with Double Layer Bi-Substituted Iron Garnet Films: Optical and Magneto-Optical Responses in Transmission and Reflection

Optical and magneto-optical spectra in transmission and reflection and their features for microcavity one-dimensional magnetophotonic crystals with double layer bismuth-substituted iron garnet films are considered. At the first presented the experimental results of magnetic circular dichroism investigations in microcavity one-dimensional magnetophotonic crystals.

Anisotropy and Field-Sensing Bandwidth in Self-Biased Bismuth-Substituted Rare-Earth Iron Garnet Films: Measurement by Ferromagnetic Resonance Spectroscopy

The high-frequency response of magneto-optic ferrites for field-sensing applications is dictated by the ferromagnetic resonance (FMR) frequency. The FMR frequency can be increased by applying an external biasing field or by tuning the internal anisotropies of the material to provide a self-bias. We report the angular dependence of FMR spectra of bismuth-substituted rare-earth iron garnet thin films to extract their uniaxial and cubic anisotropies. These measurements allow us to estimate the characteristic resonant frequency in the self-bias regime, which is equivalent to the high-frequency limit for magnetic field-sensing in these materials when no external field is applied. We find that the frequency limit estimated by FMR agrees with the measured frequency limit of a magneto-optic field sensor utilizing the same garnet composition.

Physical Properties and Behaviour of Highly Bi-Substituted Magneto-Optic Garnets for Applications in Integrated Optics and Photonics

Rare-earth and Bi-substituted iron garnet thin film materials exhibit strong potential for application in various fields of science and frontier optical technologies. Bi-substituted iron garnets possess extraordinary optical and MO properties and are still considered as the best MO functional materials for various emerging integrated optics and photonics applications. However, these MO garnet materials are rarely seen in practical photonics use due to their high optical losses in the visible spectral region. In this paper, we report on the physical properties and magneto-optic behaviour of high-performance RF sputtered highly bismuth-substituted iron garnet and garnet-oxide nanocomposite films of generic composition type (Bi, Dy/Lu)3(Fe, Ga/Al)5O12. Our newly synthesized garnet materials form high-quality nanocrystalline thin film layers which demonstrate excellent optical and MO properties suitable for a wide range of applications in integrated optics and photonics.

Second harmonic generation study of internallygenerated strain in bismuth-substituted iron garnet films

The present article highlights the lattice-imperfection and compositional origins of the nonlinear optical response in bismuth-substituted iron garnet films. In particular the roles of lattice mismatch strain and micro-strain on second harmonic generation in (Bi,Y)(3)(Fe,Ga)(5)O(12) films are elucidated based on experimental findings. It is found that lattice mismatch strain drives the second harmonic signal in (Bi,Y)(3)(Fe,Ga)(5)O(12) films, in agreement with theoretical predictions; however micro-strain was found not to correlate significantly with the second harmonic signal at the micro-strain levels present in these samples. The present study also elaborates on the influence of the film's constitutive elements and finds the nonlinear response to increase with yttrium concentration.

Imaging Capabilities of Bismuth Iron Garnet Films With Low Growth-Induced Uniaxial Anisotropy

The study of the imaging capabilities of the bismuth substituted iron garnet films with low growth-induced uniaxial anisotropy is reported. The dependence of the film properties and imaging sensitivity on the lattice mismatch and film thickness is discussed. A simulation of the dependence of the magnetic free energy density on the magnetization orientation is performed in order to study the local energy minima and draw conclusions about the film sensitivity to different lattice mismatch parameters.