Magneto-optical Spectroscopy Research Articles

The visible magneto-optical response of RE1-xAxMnO3manganites: relationship with the charge component of the material.

Magnetic circular dichroism (MCD) spectroscopy for manganite films of various compositions and morphologies has been studied in the range of 1.2-3.7 eV. The primary focus was on the temperature behavior of the MCD spectra, as well as the magnetization and resistivity of the films. The data obtained were analyzed in comparison with magneto-optical spectroscopy of the Kerr rotation (KR) on both single crystal and thin film of manganites. It has been established that the MCD response at 2.3 eV is typical for manganites transitioning into a conducting state. Consequently, it reflects a change in the band structure of the material. This response is also observed in the KR spectrum of manganites in the range 2.3-2.6 eV below the metal-insulator transition temperature. These findings complement the understanding of the electronic structure of manganites in general. Moreover, they also provide a basis for the search for new functional materials.

Polar magneto-optical Kerr effect spectroscopy with a microscope arrangement for studies on 2D materials.

We describe a setup for magneto-optical Kerr effect (MOKE) spectroscopy suitable for Kerr rotation (ϕ) and ellipticity (η) measurement on microscopic samples, such as flakes of two-dimensional materials. A spatial resolution of ∼25μm, limited by the demagnified monochromator exit slit image, was achieved. The use of mirrors allows for measurement in polar MOKE geometry with a conventional electro-magnet, without requiring holes in the magnet pole pieces. The microscope-like optics also has a 90° twisted periscope arrangement of two mirrors that helps transport light without change in its circular polarization state. A Jones matrix analysis of the setup brings out the influence of the beam-splitter on the measured signals. Its correction requires the ellipsometry parameters of the beam-splitter in transmission mode, which were measured separately. The working of the setup is tested by measuring the ϕ and η spectra of 2H-WS2 flakes at low temperature, verifying them using Kramers-Kronig analysis and extracting the Landé g-factor of the ground state exciton from them.

Relationship between magnetic asymmetry and magnetization in ultrafast transverse magneto-optical Kerr effect spectroscopy in the extreme ultraviolet spectral range

Relationship between magnetic asymmetry and magnetization in ultrafast transverse magneto-optical Kerr effect spectroscopy in the extreme ultraviolet spectral range

Direct Determination of Carrier Parameters in Indium Tin Oxide Nanocrystals.

We develop here a comprehensive experimental approach to independently determine charge carrier parameters, namely, carrier density and mass, in plasmonic indium tin oxide nanocrystals. Typically, in plasmonic nanocrystals, only the ratio between these two parameters is accessible through optical absorption experiments. The multitechnique methodology proposed here combines single particle and ensemble optical and magneto-optical spectroscopies, also using 119Sn solid-state nuclear magnetic resonance spectroscopy to probe the surface depletion layer. Our methodology overcomes the limitations of standard fitting approaches based on absorption spectroscopy and ultimately gives access to carrier effective mass directly on the NCs, discarding the use of literature value based on bulk or thin film materials. We found that mass values depart appreciably from those measured on thin films; consequently, we found carrier density values that are different from reported literature values for similar systems. The effective mass was found to deviate from the parabolic approximation at a high carrier density. Finally, the dopant activation and defect diagram for ITO NCs for tin doping between 2.5 and 15% are determined. This approach can be generalized to other plasmonic heavily doped semiconductor nanostructures and represents, to the best of our knowledge, the only method to date to characterize the full Drude parameter space of 0-D nanosystems.

Polaronic Mass Enhancement and Polaronic Excitons in Metal Halide Perovskites.

In metal halide perovskites, the complex dielectric screening together with low energy of phonon modes leads to non-negligible Fröhlich coupling. While this feature of perovskites has already been used to explain some of the puzzling aspects of carrier transport in these materials, the possible impact of polaronic effects on the optical response, especially excitonic properties, is much less explored. Here, with the use of magneto-optical spectroscopy, we revealed the non-hydrogenic character of the excitons in metal halide perovskites, resulting from the pronounced Fröhlich coupling. Our results can be well described by the polaronic-exciton picture where electron and hole interactions are no longer described by a Coulomb potential. Furthermore, we show experimental evidence that the carrier-phonon interaction leads to the enhancement of the carrier's effective mass. Notably, our measurements reveal a pronounced temperature dependence of the carrier's effective mass, which we attribute to a band structure renormalization induced by the population of low-energy phonon modes. This interpretation finds support in our first-principles calculations.

High-harmonic spin-shearing interferometry for spatially resolved EUV magneto-optical spectroscopy

We present a method for achieving hyperspectral magnetic imaging in the extreme ultraviolet (EUV) region based on high-harmonic generation (HHG). By interfering two mutually coherent orthogonally-polarized and laterally-sheared HHG sources, we create an EUV illumination beam with spatially-dependent ellipticity. By placing a magnetic sample in the beamline and sweeping the relative time delay between the two sources, we record a spatially resolved interferogram that is sensitive to the EUV magnetic circular dichroism of the sample. This image contains the spatially-resolved magneto-optical response of the sample at each harmonic order, and can be used to measure the magnetic properties of spatially inhomogeneous magnetic samples.

Elucidating Singlet-Fission-Born Multiexciton Dynamics via Molecular Engineering: A Dilution Principle Extended to Quintet Triplet Pair.

Multiexciton in singlet exciton fission represents a critical quantum state with significant implications for both solar cell applications and quantum information science. Two distinct fields of interest explore contrasting phenomena associated with the geminate triplet pair: one focusing on the persistence of long-lived correlation and the other emphasizing efficient decorrelation. Despite the pivotal nature of multiexciton processes, a comprehensive understanding of their dependence on the structural and spin properties of materials is currently lacking in experimental realizations. To address this gap in knowledge, molecular engineering was employed to modify the TIPS-tetracene structures, enabling an investigation of the structure-property relationships in spin-related multiexciton processes. In lieu of the time-resolved electron paramagnetic resonance technique, two time-resolved magneto-optical spectroscopies were implemented for quantitative analysis of spin-dependent multiexciton dynamics. The utilization of absorption and fluorescence signals as complementary optical readouts, in the presence of a magnetic field, provided crucial insights into geminate triplet pair dynamics. These insights encompassed the duration of multiexciton correlation and the involvement of the spin state in multiexciton decorrelation. Furthermore, simulations based on our kinetic models suggested a role for quintet dilution in multiexciton dynamics, surpassing the singlet dilution principle established by the Merrifield model. The integration of intricate model structures and time-resolved magneto-optical spectroscopies served to explicitly elucidate the interplay between structural and spin properties in multiexciton processes. This comprehensive approach not only contributes to the fundamental understanding of these processes but also aligns with and reinforces previous experimental studies of solid states and theoretical assessments.

Magneto-optical and high-frequency electron paramagnetic resonance spectroscopy of Er3+ ions in CaMoO4 single crystal

We present the optical and magneto-optical spectroscopy and electron paramagnetic resonance (EPR) investigations of CaMoO4 single crystals doped with the erbium ions. Telecom-wavelength resonance transition inhomogeneous line width of Er3+ is relatively narrow for oxide crystals which makes this material promising for quantum technologies applications. The hyperfine structure in optical spectra of 167Er3+ isotope is well resolved. Energies and symmetries of wavefunctions of 39 energy levels of Er3+ ions in the crystal-field (CF) of S4 symmetry and g-factors of some CF Kramers doublets were measured and successfully simulated on the basis of CF calculations. The obtained set of CF parameters was used for modeling the hyperfine structure profiles observed in the optical absorption spectra.

Towards spin state tailoring of charged excitons in InGaAs quantum dots using oblique magnetic fields

We investigate the effect of oblique magnetic field configurations on a singly charged self-assembled quantum dot system as a means to tune the spin composition of the ground electron spin eigenstates. Using magneto-optical spectroscopy and Stokes polarimetry techniques, we evaluate the anisotropic g factors and characterize the polarization properties of the charged quantum dot system under oblique fields. We compare the results to a simple model that captures the resulting level structure and polarization selection rules for arbitrary magnetic field orientations. Under oblique magnetic fields, the system's ground spin eigenstates are composed of unequal superpositions of the electron spins. This provides an additional degree of freedom to tailor the composition of the ground spin states in charged quantum dots and based on this we demonstrate spin pumping and initialization of the tailored ground states, confirming that the double-Λ level structure of the charged quantum dot persists in oblique magnetic fields. These combined results show that the uneven weightings of the tailored spin states can yield systems with interesting behaviors, with a potential towards developing spin-selective readout schemes to further enhance the capabilities of spin qubits. Published by the American Physical Society 2024

Electron-Withdrawing meso-Substituents Turn On Magneto-Optical Activity in Porphyrins.

A series of square planar metalloporphyrins (M(TPP), TPP is 5,10,15,20-tetraphenylporphyrin and M(TPFPP), TPFPP is 5,10,15,20-tetrapentafluorophenylporphyrin; M is Zn2+, Ni2+, Pd2+, or Pt2+) with distinct meso-substituents were prepared, and their magneto-optical activity (MOA) was characterized by magnetic circular dichroism (MCD) and magneto-optical rotary dispersion spectroscopy (MORD; also known as Faraday rotation spectroscopy). MOA is crucial in the development of next-generation magneto-optical devices and quantum computing. The data show that the presence of meso-pentafluorophenyl substituents results in significant increase in MOA in comparison to the homologous phenyl group. Differences in the MOA of these metalloporphyrins are rationalized using the Gouterman four-orbital model and pave the way for rational design of improved and tailorable magneto-optical materials.

Remote detection of the conductivity of current-carrying metallized traces

The weak magnetic fields generated by a current-carrying metallized traces are detected in view of their applications in bionic systems and neural-electrode interface technologies. The traces are formed by femtosecond laser processing of the surface of polydimethylsiloxane polymer substrate and further functionalization by electroless metallization. The measurements are performed by means of magneto-optical spectroscopy involving two optical beams, serving as pump and probe, where the magnetic field sensor is 87Rb atoms confined in a paraffin-coated optical cell. The experimental results show the feasibility of remote detection of the conductivity of metallized nickel traces.

Tuning ultrafast demagnetization dynamics in FePdPt ternary alloy films: the role of spin–orbit coupling

The influence of spin–orbit coupling (SOC) on ultrafast demagnetization dynamics is still an obscure issue. Ferromagnetic ternary alloy film containing Platinum element has the advantage that SOC strength can be regulated flexibly by varying the component ratio, thus is an excellent platform for investigating the dynamical effect of SOC. Here the fluence and component dependences of ultrafast demagnetization dynamics in ternary alloy L10-Fe0.5(Pd1-xPtx)0.5 films are studied by using time-resolved magneto-optical Kerr spectroscopy. An excitation-fluence dependent transition of demagnetization dynamics shows the Elliott-Yafet (EY) spin-flip scattering as the dominant mechanism of ultrafast demagnetization. We analyze the dynamics by a compatible fitting model and extract multiple characteristic time constants. It is clearly demonstrated that the gradual enhancement of SOC in fact decreases the spin-flip scattering and slow down the demagnetization process. We further show that the demagnetization time τm scales with the SOC strength ξ approximately under a dependence of τm∝ξ1/3, while a linear dependence exists between the spin–lattice relaxation time τs-l and ξ-6. These findings clarify the role of SOC in EY-dominated demagnetization dynamics and demonstrate an approach for tuning the speeds and duration of ultrafast demagnetization by regulating SOC strength.

Magnetic-field-induced spin reorientation in TmFeO<sub>3</sub> single crystals

TmFeO<sub>3</sub> exhibits rich physical properties such as magneto-optical effect, multiferroicity, and spin reorientation, making it possess significant research value in condensed matter physics and materials science. In this study, we utilize a time-domain terahertz magneto-optical spectroscopy system to investigate the changes in spin resonance frequency of TmFeO<sub>3</sub> single crystal at <i>T</i> = 1.6 K under external magnetic fields in a range of 0–7 T. The TmFeO<sub>3</sub> sample is grown in an optical floating zone furnace and its crystallographic orientation is determined by using back-reflection Laue X-ray photography with a tungsten target. The measurement setup is a self-built time-domain terahertz magneto-optical spectroscopy system, with magnetic fields in a range of 0–7 T, temperatures in a range of 1.6–300 K, and a spectral range of 0.2–2.0 THz. A pair of 1 mm-thick ZnTe nonlinear crystals is used to generate and detect terahertz signals through optical rectification and electro-optic sampling technique. The system variable temperature and magnetic field are controlled by a superconducting magnet. In experiments, a linearly polarized terahertz wave is vertically incident on the sample surface, and its magnetic component <i>H</i><sub>THz</sub> is parallel to the sample surface. By rotating the sample, the angle (<i>θ</i>) between macroscopic magnetic moment <i> <b>M</b> </i> and <i>H</i><sub>THz</sub> can be tuned, achieving selective excitations of the two modes, that is, <i>θ</i> = 0 for q-AFM mode and 90° for q-FM mode. Terahertz absorption spectrum results indicate that as the magnetic field increases, the quasi-ferromagnetic resonance (q-FM) of TmFeO<sub>3</sub> single crystal shifts towards high frequencies, and quasi-antiferromagnetic resonance (q-AFM) transits to q-FM under low critical magnetic fields (2.2–3.6 T). Through magnetic structure analysis and theoretical fitting, it is confirmed that the magnetic moment of the single crystal undergoes magnetic field induced spin reorientation. This study is helpful in better understanding of the regulation mechanism of the internal magnetic structure of rare earth ferrite under the combined action of external magnetic field and temperature field, and also in developing related spin electronic devices.

Magnitoopticheskaya kerr-spektroskopiya nanokompozitov

Magnetooptical spectroscopy is an effective method for studying the magnetic microstructure of homogeneous and heterogeneous magnets. This review is devoted to analysis of numerous factors affecting the intensity and spectral dependence of a magnetooptical signal of the equatorial Kerr effect in nanocomposites “ferromagnetic metal–dielectric” in the visible and near infrared spectral regions. Examples of the influence of the metal concentration, nanoparticle size and shape, the substrate, the material of the dielectric, the amorphization of grains, the deposition method, and other factors on the magnetooptical spectrum are considered. The differences in the magnetooptical spectra for the superparamagnetic, superferromagnetic, and ferromagnetic states are demonstrated. It is noted that in the presence of fractions with different field dependences of the magnetization in a nanocomposite, the magnetooptical signal is not proportional to the total magnetization. Examples of enhancement and sign inversion of the magnetooptical signal in nanocomposites are considered. The possibility of the description of magnetooptical spectra using the methods of the effective medium (the Bruggeman method and the Maxwell–Garnett symmetrized approximation) is discussed.

Collinear and noncollinear ferrimagnetic phases in Mn4N investigated by magneto-optical Kerr spectroscopy

Ferrimagnetic antiperovskite Mn4N has received growing interest due to room-temperature observation of large perpendicular magnetic anisotropy, low saturation magnetization, and ultrafast response to external magnetic fields. Comprehensive understanding of the underlying magnetic structure is instrumental in design and fabrication of computer memory and logic devices. Magneto-optical spectroscopy provides deeper insight into the magnetic and electronic structure than magnetometry. Simulations of a magneto-optical Kerr effect in biaxially strained Mn4N are performed using density functional theory and linear response theory. We consider three ferrimagnetic phases, two collinear and one noncollinear, which have been investigated separately by earlier studies. The simulated spectra are compared to measured magneto-optical data available in recent literature. One of the collinear ferrimagnetic phases is found to be consistent with the measured spectra. We show that an admixture of the noncollinear phase, which is the ground state of unstrained Mn4N, further improves the agreement with measured spectra, and at the same time, it could explain the lower than predicted net moment and magnetic anisotropy observed in thin films on various substrates.

Magneto-Optical Sensing of the Pressure Driven Magnetic Ground States in Bulk CrSBr.

Competition between exchange interactions and magnetocrystalline anisotropy may bring new magnetic states that are of great current interest. An applied hydrostatic pressure can further be used to tune their balance. In this work, we investigate the magnetization process of a biaxial antiferromagnet in an external magnetic field applied along the easy axis. We find that the single metamagnetic transition of the Ising type observed in this material under ambient pressure transforms under hydrostatic pressure into two transitions, a first-order spin-flop transition followed by a second-order transition toward a polarized ferromagnetic state near saturation. This reversible tuning into a new magnetic phase is obtained in layered bulk CrSBr at low temperature by varying the interlayer distance using high hydrostatic pressure, which efficiently acts on the interlayer magnetic exchange and is probed by magneto-optical spectroscopy.

Observation of anomalous Hall resonance of massive Dirac fermions in topological kagome-lattice magnet

The kagome-lattice materials promise emergence of Dirac fermions thanks to the special lattice geometry, which potentially realizes intriguing quantum topological states through various many-body interactions. The low-energy electromagnetic phenomena arising from such the Dirac fermions are expected to show the remarkable enhancement and, in certain conditions, to approach the universal responses, which, however, have remained elusive experimentally. Here, we show the resonantly enhanced magneto-optical response of massive Dirac fermions in kagome-lattice magnet TbMn6Sn6. The infrared magneto-optical spectroscopy reveals that the interband transition on massive Dirac bands significantly contributes to the observed resonance in the optical Hall conductivity. The analytical model expressed by a few band parameters reproduces the spectral characteristics of the resonance, which robustly produces almost 20 % of the quantized Hall conductance per one kagome layer even at room temperature. Our findings establish the general optical response of massive Dirac fermions, which is closely related to the universal electrodynamics in quantum anomalous Hall state.

Magnetic-field-induced spin reorientation in a c-cut TmFeO3 single crystal observed by terahertz spectroscopy

In this study, we utilized time-domain terahertz magneto-optical spectroscopy to investigate the spin resonance in a c-cut TmFeO3 single crystal at T = 1.6 K under different magnetic fields and characterized its intricate internal interactions. By selectively exciting the magnetic resonance modes in the crystal, we found that as the magnetic field increases, the quasi-ferromagnetic (q-FM) mode of TmFeO3 single crystal shifts towards higher frequencies, while the quasi-antiferromagnetic (q-AFM) mode transforms into the q-FM mode at low critical magnetic fields (2.2–3.6 T). Through magnetic structure analysis and theoretical calculations, it is confirmed that the magnetic moment of TmFeO3 undergoes a magnetic-field-induced spin reorientation from Γ2 to Γ4 phase. Materials with magnetic moment flipping at low magnetic fields may find applications for antiferromagnetic spintronic devices in the future.

Energy gap of topological surface states in proximity to a magnetic insulator

Topological surface-states can acquire an energy gap when time-reversal symmetry is broken by interfacing with a magnetic insulator. This gap has yet to be measured. Such topological-magnetic insulator heterostructures can host a quantized anomalous Hall effect and can allow the control of the magnetic state of the insulator in a spintronic device. In this work, we observe the energy gap of topological surface-states in proximity to a magnetic insulator using magnetooptical Landau level spectroscopy. We measure Pb1-xSnxSe–EuSe heterostructures grown by molecular beam epitaxy exhibiting a record mobility and low Fermi energy. Through temperature dependent measurements and theoretical calculations, we show this gap is likely due to quantum confinement and conclude that the magnetic proximity effect is weak in this system. This weakness is disadvantageous for the realization of the quantum anomalous Hall effect, but favorable for spintronic devices which require the preservation of spin-momentum locking at the Fermi level.

The coupling between the interlayer magnetic order and Davydov splitting modes in few-layer CrI3

The magnetic order in 2D material CrI3 has a significant impact on the Raman polarization selection rules of phonons, as evidenced by magneto-optical Raman spectroscopy. In a monolayer, the forbidden Raman scattering of A1g mode can be detected in the XY channel at low temperatures. However, in the bilayer, the Ag mode splits into two modes, and the selection rules of the splitting modes are determined by the magnetic order and symmetry. In contrast, the inversion symmetry of the spin structure is maintained in both antiferromagnetic (AFM) and ferromagnetic (FM) states in the trilayer (3L) CrI3, and the evolution of its Raman scattering with magnetic field is not yet clear. In this work, we use magneto-optical polarized Raman spectroscopy and reflective magnetic circular dichroism to investigate the Davydov splitting of the Ag phonon mode and its coupling to layered magnetism in 2–5L CrI3. Our results show that the Raman scattering of the Ag mode is strongly coupled to the layered magnetic order, indicating strong spin–phonon coupling in CrI3. Our study might shed light on the research on interaction between magnetic and vibrational properties of 2D magnetic materials and provide important implications for developing novel 2D spintronic devices.