Effect of Co-60 gamma-ray irradiation on electrical properties of Ti/Au/GaAs1-xNx Schottky diodes

Current-voltage (I-V), capacitance-voltage-frequency (C-V-f) and conductance-voltage-frequency (G/ω-V-f) measurements at room temperature are used to study 50 kGy 60Co γ-ray electrical properties irradiation dependence of Ti/Au/GaAs1−xNx Schottky diodes with 0.2%; 0.4%; 0.8% and 1.2% nitrogen dilution. This γ-ray irradiation induces a permanent damage that has increased ideality factor and series resistance for all samples. It was accompanied by a decrease in Schottky barrier height with nitrogen content up to 0.4%N and remained constant thereafter. Radiation was also found to degrade the reverse leakage current. At high frequency (1 MHz), capacitance and conductance decreased after radiation due to a decrease in net doping concentration. Interface state density and series resistance were determined from C-V-f and G/ω-V-f characteristics using Hill-Coleman methods. Interface states density exponentially decreased with increasing frequency confirming the behavior of interface traps response to ac signal. Series resistance increases after irradiation is attributed to carrier's removal effect and mobility degradation. It has two peaks in the accumulation and inversion region for some diodes (0.4%N, 0.8%N). γ-ray irradiation produced traps levels and recombination centers that reduce relaxation time. An increase in %N content can impede irradiation damage with even some compensation when the percent of diluted nitrogen is high (1.2%N)

In-Situ X-Rays Diffraction and Multiscale Modeling of Shape Memory Alloys

International audienceIncreasing use of Shape Memory Alloys (SMA) for complex applications requires a robust modeling of phenomena governing their behavior. The development of micro-macro multiaxial model is relevant. Such approach relies the definition of transition scale rules, depending on the microstructure, and a description of the behavior of constituents. On the other hand, it requires experiments for identification of parameters such as enthalpies or kinetic constants and validation of the model. In this paper, in situ X-Ray Diffraction (XRD) measurements are performed during tensile tests and heating-cooling cycles. XRD permits monitoring of the average volume fraction of phases in presence. Results will be used for the validation of a multiscale and multiphased model

Single shot ultrafast all optical magnetization switching of ferromagnetic Co/Pt multilayers

The ability to control magnetism in sub-picosecond timescales using laser pulses has potential applications in fast magnetic devices. It has been demonstrated that a single femto-second laser pulse can reverse -The magnetization of a film within a few picoseconds [1], a phenomenon called as all-optical switching (AOS). However, this phenomenon thus far has been observed only in ferrimagnetic GdFeCo films. On -The o-Ther hand, ferromagnetic films, which are of greater interest than ferrimagnets in many technological applications, need multiple laser pulses for magnetization reversal [2], making -The overall effect slow and energy inefficient. Fast, singleshot switching of a ferromagnet can open up new avenues for spintronic devices that operate at unprecedented picosecond timescales, -Thereby making -Them viable non-volatile replacements for silicon based RAMs and logic devices

Single shot ultrafast all optical magnetization switching of ferromagnetic Co/Pt multilayers

A single femto-second optical pulse can fully reverse the magnetization of a film within picoseconds. Such fast operation hugely increases the range of application of magnetic devices. However, so far, this type of ultrafast switching has been restricted to ferri-magnetic GdFeCo films. In contrast, all optical switching of ferro-magnetic films require multiple pulses, thereby being slower and less energy efficient. Here, we demonstrate magnetization switching induced by a single laser pulse in various ferromagnetic Co/Pt multilayers grown on GdFeCo, by exploiting the exchange coupling between the two magnetic films. Table-top depth-sensitive time-resolved magneto-optical experiments show that the Co/Pt magnetization switches within 7 ps. This coupling approach will allow ultrafast control of a variety of magnetic films, which is critical for applications

Ultrafast magnetic memory bits using all-optical magnetic switching

Up until now, magnetic nanodots used for magnetic random access memory have required spin-polarized currents to transfer the angular momentum needed to switch the magnetization and thereby switch the magnetic memory bit. This particular switching process, however, is limited to nanosecond or greater timescales-too slow for use as low-level cache in energy efficient electronics systems. On the other hand, this work aims to achieve ultrafast femtosecond switching of nanomagnetic dots without the use of spin-polarized currents. Using just linearly polarized light, several research groups have demonstrated all-optical magnetization switching in large GdFeCo magnetic dots, ranging from several microns [1-4] down to 400 nm [5]; this work characterizes the switching behavior as these dots are scaled down further in size, with the aim of minimizing the energy required for switching the magnetic memory bit. The fabrication process, magnetization behavior and optical switching behavior are additionally characterized to better understand how size affects the functionality of these optically-switchable ferrimagnets. Knowledge of this behavior will allow future developments of simultaneously ultrasmall and ultrafast magnetic memory systems, thereby enabling increased data storage in future electronics

Direct optical detection of current induced spin accumulation in metals by magnetization-induced second harmonic generation

International audienceStrong spin-orbit coupling in non-magnetic heavy metals has been shown to lead to large spin currents flowing transverse to a charge current in such a metal wire. This in turn leads to the buildup of a net spin accumulation at the lateral surfaces of the wire. Spin-orbit torque effects enable the use of the accumulated spins to exert useful magnetic torques on adjacent magnetic layers in spintronic devices. We report the direct detection of spin accumulation at the free surface of nonmagnetic metal films using magnetization-induced optical surface second harmonic generation. The technique is applied to probe the current induced surface spin accumulation in various heavy metals such as Pt, β-Ta, and Au with high sensitivity. The sensitivity of the technique enables us to measure the time dynamics on a sub-ns time scale of the spin accumulation arising from a short current pulse. The ability of optical surface second harmonic generation to probe interfaces suggests that this technique will also be useful for studying the dynamics of spin accumulation and transport across interfaces between non-magnetic and ferromagnetic materials, where spin-orbit torque effects are of considerable interest