239 research outputs found
Effect of linear polarisability and local fields on surface SHG
A discrete dipole model has been developed to describe Surface Second Harmonic Generation by centrosymmetric semiconductors. The double cell method, which enables the linear reflection problem to be solved numerically for semi-infinite systems, has been extended for the nonlinear case. It is shown that a single layer of nonlinear electric dipoles at the surface and nonlocal effects allows to describe the angle of incidence dependent anisotropic SHG obtained from oxidised Si(001) wafers. The influence of the linear response, turns out to be essential to understand the anisotropic SHG-process
Observation of strong surface state effects in the nonlinear magneto-optical response of Ni(110)
Spectroscopic magnetization induced optical Second Harmonic Generation (MSHG)
measurements from a clean Ni(110) surface reveal strong resonance effects near
2.7 eV that can be attributed to the presence of an empty surface state. The
good agreement with model calculations shows the potential of MSHG to probe
spin polarized interface band structures.Comment: REVTeX/EPS figures/Authors's single Postsript file, to appear in PRL,
our new phase-sensitive detection technique is used (see PRB, 58, R16020
(1998)), for more details see http://www.sci.kun.nl/tvs/people/petukhov
Stable and fast semi-implicit integration of the stochastic Landau-Lifshitz equation
We propose new semi-implicit numerical methods for the integration of the
stochastic Landau-Lifshitz equation with built-in angular momentum
conservation. The performance of the proposed integrators is tested on the 1D
Heisenberg chain. For this system, our schemes show better stability properties
and allow us to use considerably larger time steps than standard explicit
methods. At the same time, these semi-implicit schemes are also of comparable
accuracy to and computationally much cheaper than the standard midpoint
implicit method. The results are of key importance for atomistic spin dynamics
simulations and the study of spin dynamics beyond the macro spin approximation.Comment: 24 pages, 5 figure
Laser induced THz emission from femtosecond photocurrents in Co/ZnO/Pt and Co/Cu/Pt multilayers
The ultrashort laser excitation of Co/Pt magnetic heterostructures can
effectively generate spin and charge currents at the interfaces between
magnetic and nonmagnetic layers. The direction of these photocurrents can be
controlled by the helicity of the circularly polarized laser light and an
external magnetic field. Here, we employ THz time-domain spectroscopy to
investigate further the role of interfaces in these photo-galvanic phenomena.
In particular, the effects of either Cu or ZnO interlayers on the photocurrents
in Co/X/Pt (X = Cu, ZnO) have been studied by varying the thickness of the
interlayers up to 5 nm. The results are discussed in terms of spin-diffusion
phenomena and interfacial spin-orbit torque.Comment: 15 pages, 6 figures, 2 table
Supervised learning of an opto-magnetic neural network with ultrashort laser pulses
The explosive growth of data and its related energy consumption is pushing
the need to develop energy-efficient brain-inspired schemes and materials for
data processing and storage. Here, we demonstrate experimentally that Co/Pt
films can be used as artificial synapses by manipulating their magnetization
state using circularly-polarized ultrashort optical pulses at room temperature.
We also show an efficient implementation of supervised perceptron learning on
an opto-magnetic neural network, built from such magnetic synapses.
Importantly, we demonstrate that the optimization of synaptic weights can be
achieved using a global feedback mechanism, such that the learning does not
rely on external storage or additional optimization schemes. These results
suggest there is high potential for realizing artificial neural networks using
optically-controlled magnetization in technologically relevant materials, that
can learn not only fast but also energy-efficient.Comment: 9 pages, 4 figure
Second harmonic generation from thin slabs in the discrete dipole approach
The nonlinear optical response of thin Si slabs is calculated using a discrete dipole approach. The s-polarized second harmonic response as a function of the angle of incidence appears to be in reasonable agreement with experimental results. The p-polarized SHG shows a high sensitivity for the shape of the polarizability profile
High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets
Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in
the equilibrium and ultrafast magnetic properties of the ferrimagnetic
rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the
magnetization compensation temperature, each of the magnetizations of the
antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis
loops. Contrary to state-of-the-art theory, which explains such loops by sample
inhomogeneities, here we show that they are an intrinsic property of the
rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and
have a non-zero orbital momentum in the ground state and, therefore, a large
magnetic anisotropy, we are able to reproduce the experimentally observed
behavior in equilibrium. The same theory is also able to describe the
experimentally observed critical slowdown of the spin dynamics in the vicinity
of the magnetization compensation temperature, emphasizing the role played by
the orbital momentum in static and ultrafast magnetism of ferrimagnets
Отражение света от нелинейно-оптической диэлектрической пленки на бигиротропной магнитоэлектрической подложке под углами, близкими к углам Брюстера
Теоретически исследовано отражение света от границы раздела диэлектрической пленки, которая характеризуется кубической оптической нелинейностью, на бигиротропной магнитоэлектрической подложке. Получены зависимости коэффициентов отражения от угла падения света для основных магнитооптических конфигураций: полярной, продольной и поперечной. Изучено влияние магнитоэлектрического и магнитооптического вкладов в электрическую поляризацию такой двуслойной структуры на состояние поляризации света, отраженного под углами, близкими к углам Брюстера.Теоретично досліджено відбиття світла від границі розподілу діелектричної плівки, яка характеризується кубічною оптичною нелінійністю, на бігіротропній магнітоелектричній підкладці. Отримано залежності коефіцієнтів відбиття від кута падіння світла для основних магнітооптичних конфігурацій: полярної, поздовжньої та поперечної. Вивчено вплив магнітоелектричного та магнітооптичного внесків в електричну поляризацію такої двошарової структури на стан поляризації світла, яке відбито під кутами, близькими до кутів Брюстера.The reflection of light from the interface of a dielectric film characterized by a cubic optical nonlinearity on a bigyrotropic magnetoelectric substrate is investigated theoretically. The incidence angle dependence of reflection coefficients are obtained for all principal magneto-optical configurations: polar, longitudinal, and transverse. The influence of magnetoelectric and magneto-optical contributions to electric polarization of the bilayered structure on polarization state of light, reflected at angles close to the Brewster angles is measured
Infrared studies of a La_(0.67)Ca_(0.33)MnO_3 single crystal: Optical magnetoconductivity in a half-metallic ferromagnet
The infrared reflectivity of a La_(0.67)Ca_(0.33)MnO_3 single crystal is studied over a broad range of temperatures (78–340 K), magnetic fields (0–16 T), and wave numbers (20–9000cm^(-1)). The optical conductivity gradually changes from a Drude-like behavior to a broad peak feature near 5000cm-1 in the ferromagnetic state below the Curie temperature T_C=307K. Various features of the optical conductivity bear striking resemblance to recent theoretical predictions based on the interplay between the double exchange interaction and the Jahn-Teller electron-phonon coupling. A large optical magnetoconductivity is observed near T_C
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