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Results for “Kerr effects”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Parameter-free treatment of a layered correlated van der Waals magnet: CrPS 4

The electronic and magnetic structure of CrPS 4 , a two-dimensional (2D) magnetic semiconductor is examined by employing the SCAN meta-GGA density functional. We find the resulting magnetic moment and band gap are in excellent agreement with experiment. From the bulk magnetic configurations, we confirm the experimentally observed A-type antiferromagnetic (A-AFM) ordered ground state with a magnetic moment of 2.78 µ B per chromium atom and band gap of 1.34 eV. To gain insight into the evolution of the ground state with layers, the total energy of each magnetic configuration is calculated for a variety of thicknesses. Monolayer CrPS 4 is predicted to be a ferromagnetic insulator with a band gap of 1.37 eV, and A-AFM for bilayer and trilayer, with band gaps of 1.35 and 1.30 eV, respectively. The electronic structure is reported for the single-, two-, and three-layer and bulk CrPS 4 . Finally, we explore the optical properties of the 2D structure and report the dielectric tensor components and Kerr parameters for the monolayer.

2-dimensional systems↗
DOE OSTI2022

Optically Induced Anisotropy in Time-Resolved Scattering: Imaging Molecular-Scale Structure and Dynamics in Disordered Media with Experiment and Theory

Time-resolved scattering experiments enable imaging of materials at the molecular scale with femtosecond time resolution. However, in disordered media they provide access to just one radial dimension thus limiting the study of orientational structure and dynamics. Here we introduce a rigorous and practical theoretical framework for predicting and interpreting experiments combining optically induced anisotropy and time-resolved scattering. Using impulsive nuclear Raman and ultrafast x-ray scattering experiments of chloroform and simulations, we demonstrate that this framework can accurately predict and elucidate both the spatial and temporal features of these experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Structural and magnetic properties of Pt/Co/Mn-based multilayers

Magnetic multilayers are a rich class of material systems with numerous highly tunable physical parameters that determine both their magnetic and electronic properties. Here, we present a comprehensive experimental study of the system Pt/Co/Mn, which extends the group of Pt / Co / X ( X = metal) multilayers that have been investigated thus far. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out of plane to in plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness, suggesting the existence of bubblelike domains—potentially even magnetic skyrmions—in the case of sufficiently thick Mn layers, which are expected to contribute to a sizable Dzyaloshinskii-Moriya interaction in the multilayer stacks. As a result, we identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Antiferromagnetic V 2 ⁢O 3 based exchange coupling

Vanadium sesquioxide (V 2 ⁢O 3 ) is a strongly correlated electronic material that famously undergoes a triple coupled first-order transition where it transitions from a paramagnetic metal with a rhombohedral structure at high temperature to an antiferromagnetic insulator with a monoclinic structure. While several studies have used one of both electronic and structural transitions to control the properties of a heterostructure, evidence of magnetic coupling has notoriously yet to be found. In this paper, we report on a robust magnetic coupling between the antiferromagnetic (AFM) V 2 ⁢O 3 and ferromagnetic (FM) Permalloy (Py) layers that results in a significant exchange bias and strain-induced coercivity enhancement. We provide a temperature and angle-dependent study of magnetic properties, which clearly indicates exchange bias at the AFM/FM interface that appears at the onset of the metal-insulator transition. The magnitude of the exchange bias is strongest when the field is applied along the [001] V 2 ⁢O 3 crystallographic orientation which corresponds to an AFM spin configuration on the [110] surface. Here, this opens the door to designing and implementing novel functionalities in transition metal oxide-based computing using the connection between magnetism and the metal-insulator transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Topological Magneto-optics in the Noncoplanar Antiferromagnet Co 1/3 ⁢NbS 2 : Imaging and Writing Chiral Magnetic Domains

Despite its tiny net magnetization, the antiferromagnetic (AFM) van der Waals material Co 1/3 ⁢NbS 2 exhibits a large transverse Hall conductivity 𝜎 𝑥⁢𝑦 even at zero applied magnetic field, which arises, as recently shown, from the topological nature of its noncoplanar “tetrahedral” AFM order. Here, this triple-𝐪 magnetic order can be regarded as the short-length-scale limit of a magnetic skyrmion lattice and has an intrinsic spin chirality. Here, we show, using optical wavelengths spanning the ultraviolet to infrared (400–1000 nm), that magnetic circular dichroism provides an incisive optical probe of the topological AFM order in Co 1/3 ⁢NbS 2 . Measurements as a continuous function of photon energy are directly compared with first-principles calculations, revealing the influence of the underlying quantum geometry on optical conductivity. Leveraging the power and flexibility of optical methods, we use scanning magnetic circular dichroism microscopy to directly image chiral AFM domains and demonstrate writing of chiral AFM domains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

X-ray study of ferroic octupole order producing anomalous Hall effect

Recently found anomalous Hall, Nernst, magnetooptical Kerr, and spin Hall effects in the antiferromagnets Mn 3 X (X = Sn, Ge) are attracting much attention for spintronics and energy harvesting. Since these materials are antiferromagnets, the origin of these functionalities is expected to be different from that of conventional ferromagnets. Here, we report the observation of ferroic order of magnetic octupole in Mn 3 Sn by X-ray magnetic circular dichroism, which is only predicted theoretically so far. The observed signals are clearly decoupled with the behaviors of uniform magnetization, indicating that the present X-ray magnetic circular dichroism is not arising from the conventional magnetization. We have found that the appearance of this anomalous signal coincides with the time reversal symmetry broken cluster magnetic octupole order. Our study demonstrates that the exotic material functionalities are closely related to the multipole order, which can produce unconventional cross correlation functionalities.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Detecting Phase-Resolved Magnetization Dynamics by Magneto-Optic Effects at 1550 nm Wavelength

We demonstrate the detection of phase-resolved magnetization dynamics with combinatorial magneto-optic Kerr and Faraday effects. The method uses a continuous-wave laser that is amplitude-modulated at the spin dynamic frequencies, and thus allows for coherent tracking of the spin dynamics, akin a “lock-in” type measurement. In particular, our method, using a single 1550-nmwavelength, probes simultaneously the ferromagnetic resonance of Y 3 Fe 5 O 12 (YIG) and Permalloy (Py = Ni 80 Fe 20 ) in a YIG-Pyhetero structure. The fiber-based magneto-optic components also have the advantage of being made into a compact, tabletop or even portable system with yet robust measurement performances. We believe that our method will be found useful in studying hybrid quantum magnonic systems and/or investigating phase-resolved spin dynamics in nanomagnet structures involving both ferromagnetic insulators and metals.

42 ENGINEERING↗
DOE OSTI2020

Probing magnon–magnon coupling in exchange coupled Y 3 Fe 5 O 12 /Permalloy bilayers with magneto-optical effects

We demonstrate the magnetically-induced transparency (MIT) effect in Y 3 Fe 5 O 12 (YIG)/Permalloy (Py) coupled bilayers. The measurement is achieved via a heterodyne detection of the coupled magnetization dynamics using a single wavelength that probes the magneto-optical Kerr and Faraday effects of Py and YIG, respectively. Clear features of the MIT effect are evident from the deeply modulated ferromagnetic resonance of Py due to the perpendicular-standing-spin-wave of YIG. We develop a phenomenological model that nicely reproduces the experimental results including the induced amplitude and phase evolution caused by the magnon–magnon coupling. Our work offers a new route towards studying phase-resolved spin dynamics and hybrid magnonic systems

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thickness dependence of electronic structure and optical properties of a correlated van der Waals antiferromagnetic NiPS 3 thin film

In this work, we study the thickness dependence of the electronic, magnetic, and optical properties of a NiPS 3 thin film, which is an antiferromagnetic charge-transfer insulator. Utilizing state-of-the-art advanced density functionals, we find the antiferromagnetic zigzag order, the band gap, and the main peaks in the dielectric tensor are all in good agreement with the corresponding experimental values. Upon thinning, the zigzag antiferromagnetic order becomes virtually degenerate with a competing Néel order, consistent with the suppression of long-range order observed by Raman spectroscopy due to strong magnetic fluctuations. Additionally, due to the robustness of the electronic band gap observed by spectroscopic ellipsometry measurements above T N , we suggest that the persistence of the band gap is driven by strong electronic correlations. Other systematic changes in electronic dispersion, effective mass, and Kerr angle with thickness are also discussed. Finally, an applied external electric field is found to suppress the band gap by up to 13%, until precipitating an insulator-metal transition at a critical field value of 0.7 eV/Å.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Super resolution for magneto-optical microscopy

Sub-diffraction limited magneto-optical microscopy, such as Kerr or Faraday effect microscopy, provide many advantages to fields of science and technology for measuring, or imaging, the magnetization structures and magnetization domains of materials. Disclosed is a method and system for performing sub-diffraction limited magneto-optic microscopy. The method includes positioning a microlens or microlens layer relative to a surface of a sample to image the surface of the sample, forming a photonic nanojet to probe the surface of the sample, and receiving light reflected by the surface of the sample or transmitted through the sample at an imaging sensor. The methods and associated systems and devices enable sub-diffraction limited imaging of magnetic domains at resolutions 2 to 8 times the classical diffraction limit.

te Velthuis, Suzanne Gabriëlle Everdine↗
DOE OSTI2024

A driven Kerr oscillator with two-fold degeneracies for qubit protection

We present the experimental finding of multiple simultaneous two-fold degeneracies in the spectrum of a Kerr oscillator subjected to a squeezing drive. This squeezing drive resulting from a three-wave mixing process, in combination with the Kerr interaction, creates an effective static two-well potential in the phase space rotating at half the frequency of the sinusoidal drive generating the squeezing. Remarkably, these degeneracies can be turned on-and-off on demand, as well as their number by simply adjusting the frequency of the squeezing drive. We find that when the detuning Δ between the frequency of the oscillator and the second subharmonic of the drive equals an even multiple of the Kerr coefficient K , Δ / K = 2 m , the oscillator displays m + 1 exact, parity-protected, spectral degeneracies, insensitive to the drive amplitude. These degeneracies can be explained by the unusual destructive interference of tunnel paths in the classically forbidden region of the double well static effective potential that models our experiment. Exploiting this interference, we measure a peaked enhancement of the incoherent well-switching lifetime, thus creating a protected cat qubit in the ground state manifold of our oscillator. Our results illustrate the relationship between degeneracies and noise protection in a driven quantum system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Layer-dependent optically induced spin polarization in InSe

Optical control of spin in semiconductors has been pioneered using nanostructures of III-V and II-VI semi-conductors, but the emergence of two-dimensional van der Waals materials offers an alternative low-dimensional platform for spintronic phenomena. Indium selenide (InSe), a group-III monochalcogenide van der Waals material, has shown promise for optoelectronics due to its high electron mobility, tunable direct band gap, and quantum transport. In addition to these confirmed properties, there are predictions of spin-dependent optical selection rules, suggesting the potential for all-optical excitation and control of spin in a two-dimensional layered material. Despite these predictions, layer-dependent optical spin phenomena in InSe have yet to be explored. Here, we present measurements of layer-dependent optical spin dynamics in few-layer and bulk InSe. Polarized photoluminescence reveals layer-dependent optical orientation of spin, thereby demonstrating the optical selection rules in few-layer InSe. Spin dynamics are also studied in many-layer InSe using time-resolved Kerr rotation spectroscopy. By applying out-of-plane and in-plane static magnetic fields for polarized emission measurements and Kerr measurements, respectively, the g factor for InSe was extracted. Further investigations are done by calculating precession values using a k · p model, which is supported by ab initio density functional theory. Comparison of predicted precession rates with experimental measurements highlights the importance of excitonic effects in InSe for understanding spin dynamics. In conclusion, optical orientation of spin is an important prerequisite for optospintronic phenomena and devices, and these first demonstrations of layer-dependent optical excitation of spins in InSe lay the foundation for combining layer-dependent spin properties with advantageous electronic properties found in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Scattering in black hole backgrounds and higher-spin amplitudes. Part I

The scattering of massless waves of helicity |$h$| = $0$, $\frac{1}{2}$, $1$ in Schwarzschild and Kerr backgrounds is revisited in the long-wavelength regime. Using a novel description of such backgrounds in terms of gravitating massive particles, we compute classical wave scattering in terms of 2 → 2 QFT amplitudes in flat space, to all orders in spin. The results are Newman-Penrose amplitudes which are in direct correspondence with solutions of the Regge-Wheeler/Teukolsky equation. By introducing a precise prescription for the point-particle limit, in Part I of this work we show how both agree for $h$ = 0 at finite values of the scattering angle and arbitrary spin orientation. Associated classical observables such as the scattering cross sections, wave polarizations and time delay are studied at all orders in spin. The effect of the spin of the black hole on the polarization and helicity of the waves is found in agreement with previous analysis at linear order in spin. In the particular limit of small scattering angle, we argue that wave scattering admits a universal, point-particle description determined by the eikonal approximation. We show how our results recover the scattering eikonal phase with spin up to second post-Minkowskian order, and match it to the effective action of null geodesics in a Kerr background. Using this correspondence we derive classical observables such as polar and equatorial scattering angles. This study serves as a preceding analysis to Part II, where the Gravitational Wave ($h$ = 2) case will be studied in detail.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

High-order ( N = 4–6) multiphoton absorption and mid-infrared Kerr nonlinearity in GaP, ZnSe, GaSe, and ZGP crystals

We report a study of high-order multiphoton absorption, nonlinear refraction, and their anisotropy in four notable mid-infrared χ (2) crystals: GaP, ZnSe, GaSe, and ZGP using femtosecond pulses at 2.35 μm with peak intensity in excess of 200 GW/cm 2 . We found that the nonlinear absorption obeys a perturbation model with multiphoton absorption (MPA) orders from N = 4–6, in agreement with the bandgaps of the crystals. A study of the role of free carrier absorption, performed by changing the pulse duration from 30 to 70 fs while maintaining a constant peak intensity, showed that, at our intensity levels, free carriers generated during the MPA process absorb much more strongly than would be expected from their known linear absorption cross section. Possible mechanisms for this anomalous behavior are high-field effects, such as intravalley scattering in the conduction band and absorption to higher lying bands. Nonlinear refractive indices were measured using (i) closed aperture Z-scan and (ii) spectral broadening due to self-phase modulation, both methods agreeing with each other.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Numerical simulation of dispersion and nonlinear characteristics of microstructured silica fibres with a thin suspended core in a wide range of their parameters

Dispersion and nonlinear characteristics of microstructured silica fibres with a thin suspended core surrounded by three, four or six air holes have been studied theoretically in the wavelength range 1 – 2 μm. It has been shown that, owing to strong fundamental mode confinement near the core, the Kerr nonlinearity coefficient can exceed the nonlinearity coefficient of standard telecom fibre SMF28e by two orders of magnitude. The large waveguide contribution allows for effective group velocity dispersion management. Estimates are presented that demonstrate the feasibility of using suspended core fibre exhibiting Kerr nonlinearity for generating non-classical light: a state with squeezed quantum fluctuations in one of the quadrature components of a cw laser signal at a wavelength near 1.55 μm. (paper)

36 MATERIALS SCIENCE↗