Strong Magneto-optical Effect Research Articles

Canted spin order as a platform for ultrafast conversion of magnons

Traditionally, magnetic solids are divided into two main classes—ferromagnets and antiferromagnets with parallel and antiparallel spin orders, respectively. Although normally the antiferromagnets have zero magnetization, in some of them an additional antisymmetric spin–spin interaction arises owing to a strong spin–orbit coupling and results in canting of the spins, thereby producing net magnetization. The canted antiferromagnets combine antiferromagnetic order with phenomena typical of ferromagnets and hold great potential for spintronics and magnonics1–5. In this way, they can be identified as closely related to the recently proposed new class of magnetic materials called altermagnets6–9. Altermagnets are predicted to have strong magneto-optical effects, terahertz-frequency spin dynamics and degeneracy lifting for chiral spin waves10 (that is, all of the effects present in the canted antiferromagnets11,12). Here, by utilizing these unique phenomena, we demonstrate a new functionality of canted spin order for magnonics and show that it facilitates mechanisms converting a magnon at the centre of the Brillouin zone into propagating magnons using nonlinear magnon–magnon interactions activated by an ultrafast laser pulse. Our experimental findings supported by theoretical analysis show that the mechanism is enabled by the spin canting.

Magnetic nanoparticles detection based on nonlinear Faraday rotation

Magnetic nanoparticles (MNPs) have attracted interest in various research fields due to their special superparamagnetic and strong magneto-optical effects, especially as contrast agents for enhancing medical imaging contrast. Using MNPs capable of generating Faraday rotation angles with higher harmonics as magnetic-optical contrast agents allows for a distinct contrast with biological tissues lacking these higher harmonics. This significantly improves the sensitivity of magnetic-optical imaging. By introducing the interaction coefficient, we propose a model for the nonlinear Faraday rotation of MNPs under the excitation of an external alternating magnetic field. Using our homemade device (which can detect rotation angles as low as approximately 2e-7 rad), we have verified that the higher harmonics of the Faraday rotation can mitigate interference from paramagnetic and diamagnetic backgrounds at lower concentrations. In the future, it is anticipated that MNPs can be utilized as magneto-optical contrast agents to achieve high-resolution in vivo imaging.

Homochiral Dy2 single-molecule magnets with strong magneto-optical Faraday effects and strong third-harmonic generation

Four pairs of enantiomers of ferromagnetically coupled Dy2 single-molecule magnets, which show both strong magneto-optical Faraday effects and strong third-harmonic generation, are directionally constructed.

Two Pairs of Homochiral Parallelogram-like Dy4 Cluster Complexes with Strong Magneto-Optical Properties.

Two pairs of homochiral Dy(III) tetranuclear cluster complexes derived from (+)/(-)-3-trifluoroacetyl camphor (D-Htfc/L-Htfc), [Dy4(OH)2(L1)4(D-tfc)2(DMF)2]·4DMF (D-1) [H2L1 = (E)-2-(2-hydroxy-3-methoxybenzylideneamino)phenol)]/[Dy4(OH)2(L1)4(L-tfc)2(DMF)2]·4DMF (L-1) and [Dy4(OH)2(L2)4(D-tfc)2(DMF)2]·2H2O·3MeCN (D-2) [H2L2 = (E)-3-(2-hydroxy-3-methoxybenzylideneamino)naphthalen-2-ol]/[Dy4(OH)2(L2)4(L-tfc)2(DMF)2]·2H2O·3MeCN (L-2), were synthesized at room temperature, which have a Dy4 parallelogram-like core. The magnetic studies revealed that D-1 exhibits single-molecule magnet (SMM) behavior under zero dc magnetic field, and its magnetic relaxation has a distinct Raman process in addition to the Orbach process, with the Ueff/k value of 57.5 K and the C value of 28.27 s-1K-2.14; while D-2 displays dual magnetic relaxation behavior at 0 Oe field, with the Ueff/k value 114.8 K for the slow relaxation process (SR) and the C value of 10.656 s-1K-5.80 for the fast relaxation process (FR), respectively. Theoretical calculations indicated that the conjugated groups (phenyl vs naphthyl) of the Schiff base bridging ligands (H2L1 and H2L2) significantly affect the intramolecular magnetic interactions between the Dy3+ ions and ultimately lead to different relaxations. Furthermore, magnetic circular dichroism (MCD) measurements showed that these two pairs of Dy4 enantiomers exhibit strong room temperature magneto-optical Faraday effects; notably, increasing the conjugated group on the Schiff base bridging ligand is beneficial to enhancing the magneto-optical Faraday effects.

A Pair of Multifunctional Cu(II)-Dy(III) Enantiomers with Zero-Field Single-Molecule Magnet Behaviors, Proton Conduction Properties and Magneto-Optical Faraday Effects.

Multifunctional materials with a coexistence of proton conduction properties, single-molecule magnet (SMM) behaviors and magneto-optical Faraday effects have rarely been reported. Herein, a new pair of Cu(II)-Dy(III) enantiomers, [DyCu2(RR/SS-H2L)2(H2O)4(NO3)2]·(NO3)·(H2O) (R-1 and S-1) (H4L = [RR/SS] -N,N'-bis [3-hydroxysalicylidene] -1,2-cyclohexanediamine), has been designed and prepared using homochiral Schiff-base ligands. R-1 and S-1 contain linear Cu(II)-Dy(III)-Cu(II) trinuclear units and possess 1D stacking channels within their supramolecular networks. R-1 and S-1 display chiral optical activity and strong magneto-optical Faraday effects. Moreover, R-1 shows a zero-field SMM behavior. In addition, R-1 demonstrates humidity- and temperature-dependent proton conductivity with optimal values of 1.34 × 10-4 S·cm-1 under 50 °C and 98% relative humidity (RH), which is related to a 1D extended H-bonded chain constructed by water molecules, nitrate and phenol groups of the RR-H2L ligand.

Effective Faraday rotator based on the TbYO3 crystal with a high Verdet constant and a high thermal conductivity.

Facing the demand of high-power laser development, a high-quality magneto-optical crystal with a high Verdet constant and a high thermal conductivity is needed. Herein, an effective Faraday rotation based on a TbYO3 single crystal with a strong magneto-optical effect, grown by the laser floating zone method, is demonstrated for the first time, to the best of our knowledge. The TbYO3 crystal has the Verdet constant which is 2.16 times (106 rad·m-1 T-1) higher than that of the TGG crystal (49 rad·m-1 T-1) at 880 nm. Additionally, the TbYO3 crystal also has a thermal conductivity of 11.8 W·m-1·K-1 and a laser-induced damage threshold of 1.59 GW·cm-2. These advantages can allow the TbYO3 crystal to be an attractive magneto-optical material.

Strong Magneto-Optical Kerr Effects in Ni-Doped ZnO Nanolaminate Structures Obtained by Atomic Layer Deposition.

The magneto-optical (MO) Kerr effects for ZnO and ZnO:Ni-doped nanolaminate structures prepared using atomic layer deposition (ALD) have been investigated. The chemical composition and corresponding structural and morphological properties were studied using XRD and XPS and compared for both nanostructures. The 2D array gradient maps of microscale variations of the Kerr angle polarization rotation were acquired by means of MO Kerr microscopy. The obtained data revealed complex behavior and broad statistical dispersion and showed distinct qualitative and quantitative differences between the undoped ZnO and ZnO:Ni-doped nanolaminates. The detected magneto-optical response is extensively inhomogeneous in ZnO:Ni films, and a giant Kerr polarization rotation angle reaching up to ~2° was established. This marks the prospects for further development of magneto-optical effects in ALD ZnO modified by transition metal oxide nanostructures.

Enhanced terahertz magneto-optical performance in substrate-free ultra-thick TbErBi:RIG crystal films

A wafer-scale single crystal thick film of rare-earth iron garnet (RIG) has been successfully produced on a 3-in. gadolinium gallium garnet (GGG) substrate using the liquid phase epitaxy method. The RIG crystal's thickness measures ∼550 μm. By removing the GGG substrate through polishing, we improved the terahertz (THz) transmittance of the RIG crystal. In the frequency range of 0.1–1.0 THz, the RIG material exhibits a large refractive index of around 4.50, with a transmittance of ∼60% and an absorption rate of only 10–50 cm−1. Furthermore, we investigated the THz magneto-optical effect in the RIG material through THz time-domain spectroscopy. The observed results demonstrate the presence and significance of the magneto-optical effect in the RIG crystal. To provide further insights, we measured the THz Faraday rotation angle of the 550 μm-thick RIG crystal using the THz-TDS system under an external magnetic field of 0.17 T. The measured Faraday rotation angle reached 22°, and the calculated Verdet constant for the RIG sample was ∼120°/mm/T. Considering these findings, our study highlights the unique properties of this wafer-scale single crystal thick film of RIG, including its low loss, high transmission, and strong magneto-optical effect in the THz range. These characteristics make it a promising candidate for various applications, such as THz magnetic polarization conversion, non-reciprocal phase shifters, and isolators.

Template-assisted growth of Co-BaTiO3 vertically aligned nanocomposite thin films with strong magneto-optical coupling effect

Template-assisted growth of Co-BaTiO3 vertically aligned nanocomposite thin films with strong magneto-optical coupling effect

Piezoelectric and magneto-optical effect of lanthanum-doped bismuth ferrite films on silicon substrate

Rhombohedral La:BiFeO3 films were successfully prepared on Si substrates by using Radio frequency magnetron sputtering method. The LaNiO3 as buffer layer is beneficial for improving the quality of the film, reducing surface roughness, and getting rid of the impure phase. The Bi0.9La0.1FeO3/LaNiO3/Si film has the largest piezoelectric coefficient with d33 reaching 4.76 pm/V, which is about 2.5 times larger than that of BiFeO3/LaNiO3/Si. The saturation magnetization and the MCD signal of BiFeO3 films are significantly enhanced by doping La3+. The MCD ellipticity of La:BiFeO3 film at 555 nm increase with the increase of La3+ concentration. Bi0.7La0.3FeO3/LaNiO3/Si film show strong magneto-optical effect with the high MCD ellipticity of 850 deg./cm, which is more than about 1.7 times larger than that of BiFeO3 film. This film is expected to be developed into a new multifunctional material with multi-field coupling of electro-opt-magnetism.

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.

Homochiral Cu6Dy3 single-molecule magnets displaying proton conduction and a strong magneto-optical Faraday effect

Zero-field single-molecule magnetic behavior and proton conductivity are integrated into homochiral 3d–4f nanoscale molecules, and strong magneto-optical coupling can be realized in the meantime, resulting in strong magneto-optical Faraday effects.

Magnetoplasmonic coupling in graphene nanodisk dimers: An extended coupled-dipole model for circularly polarized states

Plasmonic coupling is one of the most important effects in compact plasmonic systems, and it has been studied intensively. In contrast, magnetoplasmonic coupling (MPC) is rarely mentioned, even in graphene nanostructures supporting the strong magneto-optic effect. Here, we theoretically investigate MPC in graphene nanodisk dimers in the presence of either parallel (case I) or antiparallel (case II) magnetic fields. We find the hybridized modes always appear for two states with same chirality, while their excitations depend on incident polarization. Moreover, two antisymmetric modes are dark in case I, but all four modes are bright in case II. To provide better insight, an extended coupled-dipole model is presented, in which the fundamental circularly polarized magnetoplasmons are decomposed into two linear and orthogonal dipoles, with a $\ensuremath{\pi}/2$ phase difference, and then the coupling is described by two linear dipoles along the two orthogonal directions separately. The parameters for the magneto-optic effect and coupling strengths are independent and can be easily extracted from their individual simulations. The eigenvalues and wave functions obtained from the model can describe well the resonance frequency and excitation strength of each hybridized mode. We finally discuss MPC in touching graphene nanodisks, where the charge transfer plasmon is immune to the magneto-optic effect, and in case II, a circular resonance state will be replaced by a linear one with the incident electric field along the touching direction. In this paper, we provide a general framework for investigating mode coupling of two circular states and pave the way to magneto-optic and plasmonic applications.

Enhancements of magneto-optical properties of GeO2-PbO-B2O3–SiO2–P2O5 glass doped Tb3+ ion

In this work, a series of terbium ion-doped GeO2-PbO-B2O3–SiO2–P2O5(GPbBSP) glasses that can be used in the field of optoelectronics such as sensors have been prepared. The effect of Tb2O3 doping content on the luminescence and magneto-optical properties of glass were discussed. The amorphous property of the glasses sample was determined by X-ray diffraction analysis. FTIR spectroscopy measurements were realized and the change of glass structure with the composition were discussed. The results show that the doping of Tb2O3 promotes the conversion of [BO3] to [BO4] units, stabilizes the glass network structures. It is found that the density, refractive index, theoretical optical alkalinity, and oxygen ion polarizability of the glass shows linear positive correlation with Tb2O3 doping concentration through theoretical calculations. Conversely, the luminescence intensity decreases gradually excited by ultraviolet light. Furthermore, the magneto-optical properties of glass have been studied systematically, the Verdet constant value reaches −137.51 rad/(T·m) when the Tb2O3 doping concentration is 40 mol%, which is higher than that of the crystal of Tb3Ga5O12(TGG). The results derived from this study will be potentially useful for the Tb3+ ion doped glass with a strong Magneto-optical Effect applying in Optical isolator.

Homochiral Ferromagnetic Coupling Dy2 Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature.

By the bridging action of the 6-chloro-2-hydroxypyridine (Hchp) ligand and the terminal coordination role of the homochiral ligand, (-)/(+)-3-trifluoroacetyl camphor (l-Htfc/d-Htfc), a pair of enantiomerically pure dysprosium(III) dinuclear complexes, [Dy2(l-tfc)4(chp)2(MeOH)2] (l-1) and [Dy2(d-tfc)4(chp)2(MeOH)2] (d-1), was obtained. Their circular dichroism (CD) spectra verified their enantiomeric nature. Magnetic investigation indicated that they exhibit ferromagnetic interaction and good zero field single-molecule magnet (SMM) properties. The Ueff/k values of l-1 and d-1 at 0 Oe are 180.5 and 181.3 K, respectively, which are large values for homochiral Dy(III) SMMs. A reasonable explanation for the magnetic properties of l-1 and d-1 was supplied by ab initio calculations. Remarkably, magnetic circular dichroism (MCD) investigation revealed that the chiral Dy2 enantiomers show a strong magneto-optical Faraday effect at room temperature, suggesting potential applications in magneto-optical devices.

Terahertz magneto-optical response of bismuth-gadolinium-substituted rare-earth garnet film.

We report the magneto-optical Faraday response of bismuth-gadolinium-substituted rare-earth iron garnet at terahertz frequencies ranging from 100 GHz to 1.2 THz. The maximum transmittance of ±45° component is about 60% near the frequency point of 0.63 THz. When the external magnetic field change from -100 mT to +100 mT, the Faraday rotation angle is between -6° and +7.5°. The overall change of ellipticity is relatively small. The maximum value of the Verdet constant is about 260 °/mm/T at 0.1 THz and then gradually decreases to 80 °/mm/T at 1.2 THz. Within the considered frequency range, the thick film exhibits magnetically tunable, non-reciprocal characters and a strong magneto-optical effect within a small external magnetic field at room temperature, which will be widely used for the terahertz isolators, circulators, nonreciprocal phase shifters, and magneto-optical modulators.

Growth of high quality Si-based (Gd2Ce)(Fe4Ga)O12 thin film and prospects as a magnetic recording media

Ce3+-doped rare-earth iron garnet is a hot magneto-optical material in the field of optical communication and information technology. However, the integration of magneto-optical devices has encountered difficulties due to the poor-quality film deposited on Si. This paper focuses on high-quality Si-based (Gd2Ce)Fe5O12 and (Gd2Ce)(Fe4Ga)O12 thin films by using radio frequency magnetron sputtering method. It was found that the introduction of Ga3+ ions can protect Ce3+ from oxidation, stabilize the garnet phase, improve the optical transmittance, and reduce the lattice mismatch between the thin film and the Si substrate. And heating the substrate at 500 ℃ is conducive to grow high-quality Si-based films. The (Gd2Ce)(Fe4Ga)O12/Si thin film has the strong Kerr magneto-optical effect and the pretty high coercivity. Moreover, this film has the obvious out-of-plane magnetic anisotropy and its vertical matrix ratio close to 1, which indicates that it has the considerable prospects for high-density perpendicular magnetic recording.

First-principles study on magneto-optical effects in the ferromagnetic semiconductors Y3Fe5O12 and Bi3Fe5O12

The magneto-optical (MO) effects not only are a powerful probe of magnetism and electronic structure of magnetic solids but also have valuable applications in high-density data-storage technology. Yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$) (YIG) and bismuth iron garnet (Bi$_3$Fe$_5$O$_{12}$) (BIG) are two widely used magnetic semiconductors with strong magneto-optical effects and have also attracted the attention for fundamental physics studies. In particular, YIG has been routinely used as a spin current injector. In this paper, we present a thorough theoretical investigation on magnetism, electronic, optical and MO properties of YIG and BIG, based on the density functional theory with the generalized gradient approximation plus onsite Coulomb repulsion. We find that both semiconductors exhibit large MO effects with their Kerr and Faraday rotation angles being comparable to that of best-known MO materials such as MnBi. Especially, the MO Kerr rotation angle for bulk BIG reaches -1.2$ ^{\circ}$ at photon energy $\sim2.4$ eV, and the MO Faraday rotation angle for BIG film reaches -74.6 $ ^{\circ}/\mu m$ at photon energy $\sim2.7$ eV. Furthermore, we also find that both valence and conduction bands across the MO band gap in BIG are purely spin-down states, i.e., BIG is a single spin semiconductor. These interesting findings suggest that the iron garnets will find valuable applications in semiconductor MO and spintronic nanodevices. The calculated optical conductivity spectra, MO Kerr and Faraday rotation angles agree well with the available experimental data. The main features in the optical and MO spectra of both systems are analyzed in terms of the calculated band structures especially by determining the band state symmetries and the main optical transitions at the $\Gamma$ point in the Brillouin zone.

Giant nonreciprocal transmission in low-biased gyrotropic metasurfaces.

Strong magneto-optical effect with low external magnetic field is of great importance to achieve high-performance isolators in modern optics. Here, we experimentally demonstrate a significant enhancement of the magneto-optical effect and nonreciprocal chiral transmission in low-biased gyrotropic media. A designer magneto-optical metasurface consists of a gyrotropy-near-zero slab doped with magnetic resonant inclusions. The immersed magnetic dopants enable efficient nonreciprocal light-matter interactions at the subwavelength scale, providing a giant macroscopic nonreciprocity and strong robustness against the bias disturbance. Microwave measurements reveal that the metasurface can act as a chiral isolator for circular polarization, with extremely weak intrinsic gyromagnetic activity. We also demonstrate its capability of signal isolation for circularly polarized antennas. Our findings provide an experimental verification of nonreciprocal photonic doping with low static magnetic fields.

Terahertz magneto-optical effect of wafer-scale La: yttrium iron garnet single-crystal film with low loss and high permittivity.

The wafer-scale La:YIG single crystal thick films were fabricated on a three-inch gadolinium gallium garnet (GGG) substrate by liquid phase epitaxy method. The terahertz (THz) optical and magneto-optical properties of La:YIG film were demonstrated by THz time domain spectroscopy (THz-TDS). The results show that a high refractive index of approximately 4.09 and a low absorption coefficient of 10-50 cm-1 from 0.1 to 1.6 THz for this La:YIG film. Moreover, the THz Faraday rotation effect of La:YIG film was measured by the orthogonal polarization detection method in THz-TDS system, which can be actively manipulated by a weak longitudinal magnetic field of up to 0.155 T. With 5 samples stacked together, the Faraday rotation angle varies linearly from -15° to 15°, and the Verdet constant of La:YIG is about 100 °/mm/T within the saturation magnetization. This magneto-optical single crystal thick film with large area shows low loss, high permittivity and strong magneto-optical effect in the THz regime, which will be widely used in magneto-optical polarization conversion, nonreciprocal phase shifter and isolator for THz waves.