Excellent Magneto-optical Properties Research Articles

Epitaxy growth of pure phase CeFeO3 thin films with high magneto-optical performance and strong vertical magnetic anisotropy

The magneto-optical effects of rare earth ferrite can be greatly improved by doping Ce3+ ions. CeFeO3 with high Ce3+ concentration has excellent magneto-optical properties in theory. And due to its perovskite structure it is more suitable to be deposited on the substrates of optical devices compared with the commercial garnet ferrite. In this paper, the pure phase CexFe2–xO3 films were successfully obtained on the quartz glass and <100>-oriented SrTiO3 crystal substrates by radio frequency magnetron sputtering. The effects of substrate and Ce:Fe ratio on the epitaxial orientation, magnetism and magneto-optical performance of films were systematically studied. For the Ce1.0Fe1.0O3/STO film, its MCD ellipticity (ψF) intensity can reach up to 4750(°)/cm in the visible band and 14090(°)/cm in near ultraviolet band. And it also shows a strong vertical magnetic anisotropy, which makes it maintain a good thermal stability when the device size is reduced. These mean that the Ce1.0Fe1.0O3/STO film has a promising application in integrated optical communication devices.

Growth Considering Lattice Mismatch and Thermal Expansion and Magneto-Optical Properties of Bismuth-Doped Rare Earth Iron Garnet Crystals

Bi3+-doped iron garnet crystals (Bi:RIG) have received extensive attention for their excellent magneto-optical properties. The quality of garnet crystals has a great relationship with mismatch in the lattice and thermal expansion between crystals and seeds. Compared with TGG seeds, Sc,Ga:YIG is more suitable as the seed for growing Bi:(HoEu)IG crystals. The crystal quality and match in the lattice and thermal expansion have been discussed. The as-grown Bi:(HoEu)IG crystal has a specific Faraday rotation angle of −467° cm–1 and shows a strong magneto-optical effect.

Strong magneto-optical effect of incongruent-melting Ce,Sc,Ca:GIG crystal with heavy Ce3+ doping

To achieve high concentration of Ce3+ ions in Gd3Fe5O12 (GIG) crystal, the structure of co-doped Sc3+ and Ce3+ ions was designed and the doping energy was evaluated by the first-principles density functional theory. Based on this, Ce,Sc,Ca:GIG crystals with centimeter size and good quality were successfully grown by an improved edge-defined film-fed growth method. The transmission, magnetism, and magneto-optical effects were investigated in detailed. The Ce-doped concentration as high as 18 at% results in the (Ce0.54Gd2.41Ca0.05) (Sc0.45Fe4.55)O12 crystal having excellent magneto-optical properties. Its Faraday rotation angle increased to about −1534 deg. cm−1 at λ = 1550 nm. Therefore, the excellent magneto-optical performances reveal that Ce,Sc,Ca:Gd3Fe5O12 crystal has great potential to be utilized for miniaturized and high performance optical isolators in 1550 nm.

Terbium (III) Oxide (Tb2O3) Transparent Ceramics by Two-Step Sintering from Precipitated Powder

As a result of preliminary air calcination and subsequent reduction in a flowing NH3 atmosphere of the precursor from the liquid precipitation method for the first time, pure-phase Tb2O3 powder with an average particle size of 135 nm was prepared. The Tb2O3 magneto-optical transparent ceramics with the average grain size of 1.3 μm were successfully fabricated by vacuum pre-sintering and hot isostatic pressing post-treatment from the as-synthesized Tb2O3 powder. In-line transmittance values of Tb2O3 ceramics reach 70.3% at 633 nm, 78.1% at 1064 nm, and 79.4% at 1400 nm, respectively. Thanks to the high intrinsic concentration of Tb3+, Tb2O3 ceramics present high Verdet constants of −427.3 and −123.7 rad·T−1·m−1 at 633 and 1064 nm, which are about 3.1 and 3.4 times higher than those of commercial Tb3Ga5O12 crystals, respectively. Due to the excellent magneto-optical properties, Tb2O3 ceramics are promising candidates for the development of Faraday isolator toward compaction used in visible and near-infrared bands.

Study of magneto-optical properties of GeO2-B2O3-P2O5-ZnO-Tb2O3 glass doped with different rare-earth ions

Paramagnetic magneto-optical glasses doped with different rare-earth ions, 32GeO2–15B2O3–5P2O5–3ZnO-45Tb2O3-RE (RE = 0, 1Ho, 1Pr, 1Er, 1Nd, 1Dy, or 1Ce), referred to as GBPZ-T45-RE magneto-optical glasses, were prepared using a high-temperature melting technique. The effects of rare-earth ion doping on the structure, physical parameters, and magneto-optical properties of these GBPZ-T45-RE glasses and the effects of incident-light wavelength and temperature on the values of the Verdet constants were researched. The refractive indexes and theoretical optical basicities of the glasses were obtained by theoretical calculations. Notably, GBPZ-T45-RE glasses exhibited a large Verdet constant and superior magneto-optical performance; especially, Ho3+ and Pr3+ ions were the most effective in improving the magneto-optical properties. In addition, the Verdet constants were affected by temperature. The Verdet constants of GBPZ-T45-Ho and GBPZ-T45-Pr were determined to be −172.44 and −175.22 rad/(T·m), respectively, under 633 nm light at 298.15 K, values that are significantly greater than that the commercial terbium gallium garnet TGG crystal (−134 rad/(T·m)). The Verdet constants of GBPZ-T45-Ho and GBPZ-T45-Pr under 633 nm light increased to −254.93 and −255.92 rad/(T·m), respectively, at 273.15 K. The excellent magneto-optical properties of these glasses should enable their widespread application in optics, electricity, magnetism, information, communications, military operations, aviation, satellite measurement and control systems, and other fields.

Magneto-optical and luminescent properties of Tb3+ ions doped GBPZ magneto-optical glass

Paramagnetic GeO2-B2O3-P2O5-ZnO (GBPZ) magneto-optical glass doped with different concentration of Tb3+ ions (20–45 mol%) was successfully prepared by high-temperature melting quenching technology. The effects of different concentrations of Tb3+ ions on the structure, magneto-optical properties and luminescence properties of GBPZ glass system were studied. Through theoretical calculation, the effective doping concentration, molar volume, oxygen packing density and theoretical optical alkalinity of Tb3+ ions in the glass were obtained and analyzed the effect of these parameters on the Verdet constant. It is worth noting that the GBPZ glass samples exhibit excellent magneto-optical properties, especially the Verdet constant value of the glass sample with Tb3+ ions doping concentration of 45 mol% reaches -168.55 rad/(T·m) at the incident light wavelength of 633 nm, which is significantly higher than the Verdet constant (-134 rad/(T·m)) of the commercially available terbium gallium garnet crystal, and the strong green emission located at 544 nm observed from the sample will contribute to GBPZ magneto-optical glass in optical field of application.

LPE growth of (NdGdBi)3Fe5O12 films with high FOM and high LIDTs at a wavelength of around 1 μm

(NdGdBi)3Fe5O12 mono-crystalline films with high magneto-optical figure of merit (FOM) and high laser-induced damage thresholds (LIDTs) at a wavelength of around 1 μm have been grown in this study. Crystal structure, phase composition, magneto-optical (MO) properties and LIDTs of the grown (NdGdBi)3Fe5O12 films were discussed in detail. Tested results show that (NdGdBi)3Fe5O12 films exhibit a low insertion loss of 0.5 dB, a high FOM of 78.7 deg/dB and a high LIDTs of 9.12 J/cm2 at 1.06 μm wavelength. Lattice constant and dopants are two key factors to determine FOM and LIDTs of Bi-doped iron garnet films grown by liquid-phase epitaxial method. The excellent MO properties and LIDTs indicate that (NdGdBi)3Fe5O12 films grown in this study have a great potential to be used in 1–1.1 μm high-power lasers.

XANES/EXAFS study of the Lu and Y incorporation in the single crystal Tb3Sc2Al3O12 Faraday rotator

Tb3Sc2Al3O12 (TSAG) is a paramagnetic insulator which, in spite of its congruent nature and excellent magneto-optical properties as Faraday rotators for optical isolators (OIs), cannot be industrially produced. The reason is that its lattice structure is so stressed that single crystals easily crack upon cooling after growth or during the cutting process. By the incorporation of a small amount of Lu, it has been demonstrated that the stress in the structure can be effectively released, and, therefore, the crystal cracking can be avoided. This has enabled the substitution of standard Tb3Ga5O12 (TGG), achieving better high-power performance and compacter OIs. In this study, the charge state and the lattice site location of Lu as well as Y dopants in TSAG are investigated by X-ray Absorption Near Edge Structure and Extended X-ray Absorption Fine Structure Analysis. Measurements on single crystal and powdered samples indicate that both dopants are incorporated in the 3+ charge state and substitute predominantly in the dodecahedral Tb-site (&amp;gt;87.5%), while a minor fraction is found in the octahedral Sc-site.

Influence of choice of substrate and film thickness on magneto-optical properties of SmFeO3 thin films

Herein, SmFeO3 thin films are prepared by using magnetron sputtering technology on quartz-glass and SrTiO3(STO)(1 0 0) substrates. The influence of film thickness and choice of substrate on film quality and growth orientation is studied in detail. Moreover, the impact of phase purity and growth orientation on optical, magnetic and magneto-optical properties is discussed. The results reveal that the film thickness and choice of substrate significantly influence the induced stresses at film/substrate interface and growth orientation of the annealed film. The as-fabricated SmFeO3 thin films have demonstrated highly crystalline structure, excellent transmittance and enhanced magneto-optical properties. Moreover, obvious anisotropy in magnetization and magneto-optical properties has been observed. The SmFeO3 films with excellent magneto-optical properties can be fabricated by selecting optimal film thickness and substrate. It is expected that SmFeO3 film is a promising material for integrated optical isolators and magneto-optical modulators.

Excessively tilted fiber grating-based vector magnetometer.

A compact optic-fiber vector magnetometer is proposed and experimentally demonstrated, which is based on an excessively tilted fiber grating (Ex-TFG) assistant with the magnetic fluid (MF). Without any complicated processing, the cladding mode resonances of the bare Ex-TFG packaged by the MF show high sensitivity to slight perturbations by the magnetic field. Due to the excellent magneto-optical properties of the MF and the azimuth-dependent refractive index sensitivity of the Ex-TFG, such a magnetometer can achieve the magnetic field intensity sensitivity of 2.45nm/mT and the orientation sensitivity of 0.41nm/deg. In addition, based on the spectral interrogation, the detection limit of the magnetic field intensity could reach around 8.1μT at the minimum wavelength measurement accuracy of 0.02nm.

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.

Magnetooptical and crystalline properties of sputtered garnet ferrite film on spinel ferrite buffer layer

The purpose of this study is to provide garnet films for volumetric magnetic holography. Volumetric magnetic holography usually employs an easily obtainable short-wavelength laser (visible light, not infrared light) with a large diffraction intensity. Bi-substituted garnet ferrite with a large Faraday rotation is promising for volumetric magnetic holography applications in the visible light region. However, a garnet film without a deteriorated layer must be obtained because a deteriorated layer (minute polycrystalline grains containing an amorphous phase) is formed during the initial deposition on a glass substrate. In particular, the required magnetooptical properties have not been obtained in a thin garnet film (100 nm or less) after annealing (1 h, 700 °C, oxygen atmosphere). Therefore, there is a need for excellent garnet films with the required magnetooptical (MO) properties even if the films are thin. By using a spinel ferrite buffer layer for garnet film deposition, we could obtain a thin garnet film with excellent MO properties. We determined the effect of the initial buffer layer on the crystallinity of the deposited garnet films by observing the film cross section. In addition, we undertook a qualitative estimation of the influence of the crystallinity and optical properties of the garnet film on a glass substrate with a spinel ferrite buffer layer.

Faraday effect of bismuth iron garnet thin film prepared by mist CVD method

Metastable bismuth iron garnet (BIG, an abbreviation of Bi3Fe5O12), one kind of garnet-type ferrites, is known to manifest very large Faraday rotation as well as low optical absorption in the visible to infrared region. We report on successful synthesis of thin film composed of single-phase BIG epitaxially grown on single-crystalline gadolinium gallium garnet (Gd3Ga5O12, GGG) substrate by using mist chemical vapor deposition (CVD) method, which is an emerging technique for preparation of thin films. The crystal structure, surface morphology, and magnetic, optical and magneto-optical properties of the resultant thin films have been explored. The BIG thin film has a relatively flat surface free from roughness compared to those prepared by other vapor deposition methods. Saturation magnetization is about 1620 G at room temperature, which is close to that expected from the ideal magnetic structure of BIG. The maximum value of Faraday rotation angle reaches 54.3 deg/µm at a wavelength of 424 nm. This value is rather large when compared with those reported for BIG thin films prepared by other techniques. The wavelength dependence of Faraday rotation angle is analyzed well in terms of the crystal electric field (CEF) level schema. Our result suggests that the mist CVD method is a simple and effective technique to synthesize BIG thin film with excellent magneto-optical properties.

Strain-controlled MO Effect on Highly Bi-substituted Neodymium Iron Gallium Garnet Thin Films

Controlling magnetization of magneto-optical materials by voltage instead of electric current is expected to reduce power consumption and miniaturize functional elements in magneto-optical devices such as magneto-optical spatial light modulator. In this study, highly Bi-substituted neodymium iron gallium garnet, Nd0.5Bi2.5Fe4.5Ga0.5O12, thin film on gadolinium gallium garnet substrate prepared by metal organic decomposition method, which has excellent magneto-optical properties in visible wavelength region, was investigated as one of candidates for such devices. The thin film was cemented on a lead zirconate titanate polycrystal chip to apply external stress to the thin film. When the stress was applied, increase of coercivity has been observed by magneto-optical Kerr microscope due to reverse magnetostrictive effect. The result suggested the possibility of the Nd0.5Bi2.5Fe4.5Ga0.5O12 thin film as strain-mediated voltage controlled magneto-optical devices.

Structure and magneto-optical properties of fine-grain garnet thin films

The structure and magneto-optical properties of fine-grain garnet thin films crystallized by the rapid recurrent thermal annealing (RRTA) method have been studied. The RRAT method has been used to crystallize BiGaDyIG garnet single-layer or BiGaDyIG/AI double-layer films and to get nanometer grain size (about 30–50 nm), which results in a large Faraday rotation angle, a smoother surface and fewer voids in the films. Meanwhile we have discovered that the Faraday rotation angle increases with the number of recurrences during the rapid annealing and quenching. With the more recurrent annealing one can not only get a strong Faraday effect, but it suppresses the appearance of DyFeO 3 phase in garnet films, which has been explained very well. By applying the new method, the as-deposited films have been succesfully crystallized to the (BiDy) 3(FeGa) 5O 12 garnet phase. They exhibited excellent magneto-optical properties with a coercivity of about 1500 Oe and effective Faraday rotation angle of 1.5°. The composition, magnetic and magneto-optical properties of the crystallized garnet films have been examined.

Effects of rapid recurrent annealing on structure and magneto-optical properties of garnet films

A new method to improve the morphology and the microstructure of sputtered bismuth-substituted garnet films for optical storage is discussed. The method employs a high ramp up rate and recurrent annealing as well as quenching in an air environment, which results in smaller grain size, smoother surface, and less void volume in the garnet films than that from a conventional oven annealing. We have discovered that samples prepared with a more recurrent annealing only appeared as a single garnet phase, and the samples with a less recurrent annealing appeared as a garnet phase as well as DyFeO3 phase. We observed the microstructure of the annealed films with scanning electron microscopy (SEM). By applying the new method, the as-deposited films had been successfully crystallized to the (BiDy)3(FeGa)5O12 garnet phase with the grain size of about 300–400 Å. They exhibited excellent magneto-optical properties with a high coercive force about 1300 Oe and an effective Kerr angle of 1.5°. The crystallization process of as-deposited amorphous films as well as the structure, composition, and magnetic and magneto-optical properties of the crystallized garnet films were examined.

Kerr Enhancement by Layer Modulation in Co/Pt Multilayers

Thus far, a good Kerr hysteresis loop has been obtained only for thickness ratios of Co to Pt lower than 0.6 in Co/Pt multilayers. It has been found in this study that perfect squareness can be obtained for ultrathin films even with a high thickness ratio of tCo/tPt=1. This is caused by diminished magnetostatic energy. Furthermore, layer-modulated structures were investigated in order to increase the Kerr rotation angle. The Co/Pt multilayers were prepared by two-source rf-magnetron sputtering. Co/Pt multilayers with perfect squareness were deposited with a Pt interlayer, which resulted in excellent magneto-optical properties. In particular, the Kerr rotation angle measured from the glass-substrate side showed a very large value, 0.73 degrees. This Kerr enhancement is due to optical interference and multiple reflection. On the other hand, another interesting phenomenon was also obtained. Kerr hysteresis showed characteristic stepwise hysteresis loops when the interlayer Pt thickness was increased. Such layer-modulated multilayers have potentiality for high-density magneto-optical recording.