Optical characterization of ferromagnetic heterostructure *interfaces and thin films

This thesis presents optical characterizations of interfaces in ferromagnetic heterostructures and thin films used for spin polarized electronic devices. In these experiments, femtosecond laser spectroscopies are exploited to investigate the interface magnetization reversal, spin precession, and band offset, which are crucial in determining the performances of spintronic devices.;First, magnetization-induced second-harmonic-generation (MSHG) is applied to study interface magnetism in a hybrid structure containing a noncentrosymmetric semiconductor---Fe/AlGaAs. The reversal process of Fe interface layer magnetization is compared with the bulk magnetization reversal. In Fe/AlGaAs (001), the interface magnetization is found to be decoupled from the bulk magnetization based on the different switching characteristics---single step switching occurs at the interface layer, whereas two-jump switching occurs in the bulk. In contrast, the interface layer in Fe/AlGaAs (110) is rigidly coupled with the bulk Fe, indicating a strong impact of electronic structure on the magnetic interaction despite the same chemical composition. Furthermore, a time-resolved MSHG study demonstrates a coherent interface magnetization precession in Fe/AlGaAs (001), implying the feasibility of fast precessional control of interfacial spin. The interface magnetization precession exhibits a higher frequency and opposite phase for a given applied field compared to the bulk magnetization precession.;Second, uniform magnetization precession in the Lac0.67Ca 0.33MnO3 (LCMO) and La0.67Sr0.33MnO 3 (LSMO) films grown on different substrates are investigated by time-resolved magneto-optic Kerr effect. The parameters of magnetic anisotropy are determined from the field dependence of the precession frequency. The strain-free LCMO films grown on NdGaO3 exhibit a uniaxial in-plane anisotropy induced by the tilting of the oxygen octahedra in NdGaO3 An easy-plane magnetic anisotropy is found in the tensile-strained films grown on SrTiO 3, whereas the compressive-strained film grown on LaAlO3 exhibits an easy normal-to-plane axis.;Third, a table-top internal photoemission system is developed to measure the band offsets across semiconductor heterointerfaces by utilizing an optical parametric amplifier as the bright light source. The conduction band offsets DeltaE c = 660 meV and 530 meV at the CdCr2Se4-GaAs and CdCrZSe4-ZnSe interfaces are determined from the threshold energies of the photocurrent spectrum. The band offset is shown to be reduced by engineering the interface bonding and stoichiometry

Constraint on intermediate-range gravity from earth-satellite and lunar orbiter measurements, and lunar laser ranging

In the experimental tests of gravity, there have been considerable interests in the possibility of intermediate-range gravity. In this paper, we use the earth-satellite measurement of earth gravity, the lunar orbiter measurement of lunar gravity, and lunar laser ranging measurement to constrain the intermediate-range gravity from lambda=1.2*10^{7}m - 3.8*10^{8}m. The limits for this range are alpha=10^{-8}-5*10^{-8}, which improve previous limits by about one order of magnitude in the range lambda=1.2*10^{7}m-3.8*10^{8}m.Comment: 8 pages, International Journal of Modern Physics D, in press (World Scientific, 2005

Phenomenological theory of the giant magnetoimpedance of composite wires

Composite wires with a three-layered structure are known to show a particularly large magnetoimpedance effect. The wires consist of a highly conductive core, an insulating layer and an outer ferromagnetic shell. In order to understand the origin of the effect a theory based on a coupling of the Maxwell equations to the Landau-Lifschitz-Gilbert equation is suggested. The theory is phenomenological in the sense that it does not account for a domain structure. However, theoretical results nicely reproduce those obtained in various measurements. Furthermore, an upper limit of the magnetoimpedance ratio for a given combination of materials can be determined.Comment: 4 pages, figure

Potential Impacts on Individuals Caused by the Invasion of NGOs into International Politics

In the contemporary world, NGOs are playing significant roles in international cooperation and globalization. This actively promotes the formation of a global society. Accompanying that, NGOs also have an increased international political influence. Against this background, some scholars believe the rise of NGOs will create an era of individuals’ emancipation from the sovereign states, while others consider that the golden age of autonomy has passed. This paper studies the essence of the association dominated by NGOs and how this association affects individuals in international politics. This paper suggests that the ideal subject for NGOs is one with clearly defined and precise goals and is isolated or compatible with other subjects lest drawing governments’ hostility. The idealized NGOs predominating over all fields may create enterprise association and also help to contribute to a closed international society. The voice of individuals will be silenced in enterprise association and closed society. Therefore, NGOs should function objectively as subsidiary subjects of civil association. If NGOs intrude into the international political field, they will harm individuals

Potential Impacts on Individuals Caused by the Invasion of NGOs into International Politics

In the contemporary world, NGOs are playing significant roles in international cooperation and globalization. This actively promotes the formation of a global society. Accompanying that, NGOs also have an increased international political influence. Against this background, some scholars believe the rise of NGOs will create an era of individuals’ emancipation from the sovereign states, while others consider that the golden age of autonomy has passed. This paper studies the essence of the association dominated by NGOs and how this association affects individuals in international politics. This paper suggests that the ideal subject for NGOs is one with clearly defined and precise goals and is isolated or compatible with other subjects lest drawing governments’ hostility. The idealized NGOs predominating over all fields may create enterprise association and also help to contribute to a closed international society. The voice of individuals will be silenced in enterprise association and closed society. Therefore, NGOs should function objectively as subsidiary subjects of civil association. If NGOs intrude into the international political field, they will harm individuals

Shape model and rotation acceleration of (1685) Toro and (85989) 1999 JD6 from optical observations

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is a net torque caused by solar radiation directly reflected and thermally re-emitted from the surface of small asteroids and is considered to be crucial in their dynamical evolution. By long-term photometric observations of selected near-Earth asteroids, it's hoped to enlarge asteroid samples with a detected YORP effect to facilitate the development of a theoretical framework. Archived light-curve data are collected and photometric observations are made for (1685) Toro and (85989) 1999 JD6, which enables measurement of their YORP effect by inverting the light curve to fit observations from a convex shape model. For (1685) Toro, a YORP acceleration $\upsilon=(3.2\pm0.3)\times10^{-9}\ \rm{rad\cdot d^{-2}}(1\sigma\ error)$ is updated, which is consistent with previous YORP detection based on different light-curve data; for (85989) 1999 JD6, it is determined that the sidereal period is $7.667749\pm 0.000009$ h, the rotation pole direction locates is at $\lambda=232\pm 2^{\circ},\ \beta = -59\pm 1^{\circ}$, the acceleration is detected to be $\upsilon = (2.4\pm0.3)\times10^{-8}\ \rm{rad\cdot d^{-2}}(1\sigma\ error)$ and in addition to obtaining an excellent agreement between the observations and model. YORP should produce both spin-up and spin-down cases. However, including (85989) 1999 JD6, the $\rm{d}\omega/\rm{d}t$ values of eleven near-Earth asteroids are positive totally, which suggests that there is either a bias in the sample of YORP detections or a real feature needs to be explained.Comment: 21 pages, 10 figure

ROTATION PERIODS OF 1660 WOOD, 7173 SEPKOSKI, 12738 SATOSHIMIKI, AND (23233) 2000 WM72

We present rotation periods of four asteroids: 1660 Wood, 7173 Sepkoski, 12738 Satoshimiki, and (23233) 2000 WM72. The observations were undertaken using the SARA (Southeastern Association for Research in Astronomy) South telescope, located in Cerro Tololo Inter-American Observatory in Chile, from 2011 December to 2012 April. The following synodic periods were found: 1660 Wood, P = 6.8088 ± 0.0002 h; 7173 Sepkoski, P = 2.44 ± 0.02 h; 12738 Satoshimiki, P = 8.708 ± 0.001 h; and (23233) 2000 WM72, P = 3.732 ± 0.003 h

Zustandsrekonstruktion mit wenigen Messungen durch Kombination von Kalman-Filterung und Compressive-Sensing

Die Signalrekonstruktion ist immer ein wichtiges Thema, wobei das Kalman-Filter eine am weitesten verbreitete Methode ist. Aber wenn es viele Zustandsgrößen gibt, brauchen wir viele Messungen. Das Compressive-Sensing (CS) ist in letzter Zeit ein sehr beliebtes Thema. Man kann mit dem Compressive-Sensing ein Signal mit sehr wenigen Messungen zu rekonstruieren, aber das Compressive-Sensing hat viele Einschränkungen. Daher kombiniert diese Arbeit das Kalman-Filter und das Compressive-Sensing, um die Anzahl der benötigten Messungen zur Zustands-schätzung zu reduzieren. Erstens schlägt diese Arbeit drei Methoden vor, um die Anforderungen von dem Compressive-Sensing abzuschwächen: dünnbesetzte Änderung, Dimensionreduzierung und Sparse-Coding-Representation. Außerdem schlägt diese Arbeit zwei Methoden zur Fusion der Informationen aus dem Kalman-Filter und dem Compressive-Sensing vor: durch die Kalman-Gleichung und durch die Pseudo-Messungen. Darüber hinaus schlägt diese Arbeit ein iteratives Verfahren zur Verbesserung der Schätzung. Im idealen Fall kann die Schätzung mit dem neuen Verfahren im Vergleich zum traditionellen Kalman-Filter um 70 Prozent verbessert werden. Dann wendet diese Arbeit das Verfahren auf rauschbehaftete und zweidimensionale Signale an und stellt fest, dass das Verfahren die Schätzung im Vergleich zum traditionellen Kalman-Filter um 25 Prozent verbessert. Schließlich analysiert diese Arbeit den Zusammenhang zwischen Fehler und Systemrauschen sowie Messunsicherheiten und kommt zu dem Schluss, dass das Verfahren bei guter Modellierung und schlechten Sensoren deutlich gute Ergebnisse liefert

FOUR COLOR OBSERVATIONS OF 2501 LOHJA

Photometric studies of asteroid 2501 Lohja were made between 2014 June 24 and 25 using the Southeastern Association for Research in Astronomy (SARA) Kitt Peak telescope with Bessell B, V, R and I filters. We obtained a synodic period of 3.81 ± 0.01h, which is consistent with previous values