Design of a vector magnet for the measurements of anisotropic magnetoresistance and rotational magneto-optic Kerr effect

A vector magnet is designed and assembled with two electromagnets to produce a rotational magnetic field in any direction within a plane. This design allows a rotation of the magnetic field without a mechanical rotation of the magnets. The fast speed of the field rotation (~10 s for a complete 360° rotation) and the stability against mechanical vibration easily overcome the slow drifting effect in anisotropic magnetoresistance (AMR) and rotational magneto-optic Kerr effect (ROTMOKE) measurements. As an example we applied this vector magnet to carry out AMR and ROTMOKE measurements on epitaxial growth of Fe(10 nm)∕MgO(001) films. The result demonstrates the stability and high quality of the vector magnet in determining the magnetic anisotropy of magnetic thin films using AMR and ROTMOKE techniques.     

Simultaneous magneto-optical Kerr effect and Sixtus-Tonks method for analyzing the shape of propagating domain walls in ultrathin magnetic wires

The controlled nucleation and propagation of magnetic domain walls in ultrathin ferromagnetic wires, such as nanowires and submicrometer wires, is extremely important for the development of new high performance magnetic domain wall logic devices. Therefore, it is equally essential to possess adequate advanced experimental investigation techniques in order to be able to achieve a comprehensive in situ analysis of as many as possible parameters related to the domain wall propagation, e.g., wall shape besides wall velocity and position. In this paper, we report on a method developed specifically for the investigation of the shape of propagating magnetic domain walls in ultrathin magnetic wires, i.e., with the diameter of the magnetic wire in the range 100-950 nm. The newly developed experimental method is based on the simultaneous use of two full-fledged experimental techniques: the magneto-optical Kerr effect for analyzing the surface effects of the passing domain wall and the Sixtus-Tonks method for the investigation of the entire moving wall. The results obtained offer essential information about the shape of the propagating magnetic domain walls, being unique to this new method.     

Accurate d-spacings from zero-order Laue zone patterns.

Experimental d-spacing values are criteria towards the identification of crystallites by electron diffraction. Conclusive identifications often rely on accurate d-spacings. It is shown here that accurate orthogonal components (in mm) for the primitive unit vectors of a zero-level diffraction pattern can be obtained through least-squares processing of (x,y) coordinates for all spots on the film. Valid vectors from the origin spot to any spot in the plane of the film are integer linear combinations of the two selected unit vectors. Accurate lengths and standard deviations for such vectors therefore can be calculated from the least-squares results. Corresponding d-spacings can then be calculated from the vector lengths on the film and the camera constant. In order to obtain d-spacing values that are not only precise, but also accurate, an accurate value of the camera constant should be used. This requires calibration of the experimental setup with reference materials in the same experimental conditions, with careful control of the sample height. For the same quality of measurements, the improvement in the accuracy of the d-spacings obtained with the proposed method is approximately proportional to the square root of the number of measurements taken. Practically, typical improvement in accuracy is about threefold, and accuracies of a fraction of a percent in d-spacings are achievable in this way. The above approach has been programmed as an option in the NRCBED program.     

Nondestructive materials characterization of irradiated nuclear pressure-vessel steel samples by the use of micromagnetic techniques and in terms of mechanical properties

The contribution reports to the state of the art in materials characterization obtained by the authors through the use of micromagnetic nondestructive testing (NDT) techniques in order to predict mechanical properties of steel samples (surveillance program) after neutron irradiation in irradiation chambers of nuclear pressure vessels. The investigations have been performed within the framework of the EURATOM project CRETE [1]. The irradiated steel samples were delivered by different European countries: two sets of specimen came from France, two came from Germany, two from the Czech Republic and one from Spain. The specimens were stored in the hot cell of the research reactor in Petten, Netherlands, where they could be handled by robots in order to perform the measurements by different inspection teams. Besides electromagnetic (one team) and micromagnetic (two teams) techniques, thermoelectric (2 teams) techniques have been applied and the results are discussed. In order to characterize microstructure states in ferromagnetic steels micromagnetic, NDT techniques were based on the interaction of Bloch walls with lattice defects such as vacancies, dissolved atoms, precipitates, dislocations, and grain-and phase-boundaries. The way the lattice defects are the pinning points of the dislocation movement under mechanical loads, i.e., how they contribute to a strengthening effect, is similar to the way the Bloch walls interact with the lattice defects under magnetic loads. In addition, magnetic strengthening is observed that can be detected, for instance, in an increase of the coercivity. The institution of the authors has developed the so-called 3MA-approach (micromagnetic, multiple-parameter, microstructure, and stress analysis) in the last decade. This approach combines the information resulting from the performance of different micromagnetic techniques (magnetic Barkhausen noise, incremental permeability, harmonic analysis of the magnetic tangential field and eddy current testing used at 3 different frequencies). The data fusion is obtained through the use of neural networks, multiple regression algorithms, or pattern recognition procedures such as the nearest neighbor approach. Various information in a calibration process is selected such that disturbing influences, for instance, heating and cooling effects, are suppressed and the signal-to-noise ratio for the target function prediction (hardness, yield strength, Charpy energy, fracture appearance transition temperature, etc.) is optimized. 3MA is performed by an intelligent transducer and a data evaluation system with which, in a time multiplexing mode, one measuring quantity after the other is selected. The results obtained at the broken halves of ISO-V-notched Charpy specimens show a good performance of the multiple regression approach, with high regression coefficients near 1 and a small residual standard deviation between modeled and destructively determined mechanical properties. However, stochastically independently selected specimens show a larger deviation than the standard error of the calibration. The reason for this phenomenon is that the plastic deformation and the residual stress are in the broken Charpy specimen. Therefore, further investigations will be concentrated on calibration on irradiated, but unbroken, Charpy specimens. This text was submitted by the authors in English.     

The direct determination of magnetic domain wall profiles by differential phase contrast electron microscopy.

A new technique for the quantitative investigation of magnetic structures in ferromagnetic thin films is proposed. Unlike previous techniques the detected signal is simply related to the magnetic induction in the film, and as such the direct determination of domain wall profiles is possible. The technique utilizes a differential phase contrast mode of scanning transmission electron microscopy in which the normal bright field detector is replaced by a split-detector lying symmetrically about the optic axis of the system. The difference signal from the two halves of the detector provides the required magnetic information. Analysis of the image formation mechanism shows that, using a commercially available scanning transmission electron microscope equipped with a field emission gun, wall profiles should be obtainable directly from most structures of interest in Lorentz microscopy. Furthermore, signal-to-noise considerations indicate that these results can be obtained in acceptably short recording times. Finally, experimental results using both polycrystalline and single crystal specimens are presented, which confirm the theoretical predictions.     

Monitoring mineral slurry flow using pulse-echo ultrasound

Ultrasound based flow measurement methods have a large potential for the mining industry and its processing plants. Ultrasound travel through dense suspensions and is not affected by the magnetic fields sometimes present in this type of equipment.A cross-correlation based method is used for localized particle velocity measurements in one and two dimensions. Simultaneously, using the same data, information about local particle concentration is extracted from the power spectral density of the backscattered signal. Experiments are carried out both in simplified geometry and in full scale equipment in an iron ore pilot benefication plant.In the simple geometry it is possible to assess the precision of the methods by comparing the measurements to theory and numerical simulations. The results from the pilot plant experiments show that these methods can be applied to real world processes.     

An anisotropic magneto resistive sensor with set/reset field

Using a set/reset magnetic field, an anisotropic magneto resistive (AMR) magnetic field sensing system was developed to reduce the low frequency noise of an AMR sensor. The magnetic field resolution of the AMR sensor was improved by about three times at the frequencies below 30 Hz and a magnetic field resolution of about 150 pT/√Hz was obtained at 1 Hz. For magnetic particle detection using an AMR sensor with set/reset method, the thermal disturbance effect was canceled well and the signal-to-noise ratio was improved by about three times.     

Maximum entropy regularization method for electrical impedance tomography combined with a normalized sensitivity map

Electrical impedance tomography (EIT) aims to estimate the electrical properties at the interior of an object from current–voltage measurements on its boundary. To overcome ill-posedness, regularization techniques such as Tikhonov regularization as well as some iterative methods were developed. In difference imaging between two different conductivity distributions, a conductivity change can be seen relatively non-negative to the medium with lower conductivity through some safeguard techniques. Therefore, the concept of maximum entropy from information theory and statistic mechanics can be used for this purpose. Furthermore, because the sensing field is “soft-field” and non-uniform, the same anomaly may produce different reconstruction signatures depending on its location within the image plane. Therefore, in this paper, maximum entropy based on general Tikhonov regularization, combined with normalized sensitivity map, is proposed to solve the inverse problem of EIT. Image reconstruction was carried out by maximum entropy regularization (MER) with a normalized sensitivity map and compared with the results from conjugate gradient method (CG), Tikhonov regularization, and CG with a normalized sensitivity map accordingly. Simulation and experiment results indicate that reconstructed images with higher quality can be obtained by MER with a normalized sensitivity map.     

Experimental study on a piston-driven type magnetic refrigeration apparatus

Magnetic refrigeration, which utilizes the magnetocaloric effect of the magnetic material, is a promising alternative refrigeration technology. It is an eco-friendly refrigeration technology using solid refrigerants instead of CFC/HCFC or HFC refrigerants. Also it is regarded as an energy-efficient refrigeration system to generate temperature difference between high- and low-temparature sides using the temperature change of magnetic refrigerants according to the change of magnetic field, without using power-consuming and noisy compressors. This paper presents some experimental results obtained from a piston-driven type magnetic refrigeration apparatus, which has two sets of concentric Halbach cylinder permanent magnets. Experimental results, which were obtained by varying the stroke and speed of the piston that is used to circulate the heat transfer fluid through AMR beds of the magnetic refrigeration apparatus, were discussed.

     

Soft magnetic tweezers: a proof of principle

We present here the principle of soft magnetic tweezers which improve the traditional magnetic tweezers allowing the simultaneous application and measurement of an arbitrary torque to a deoxyribonucleic acid (DNA) molecule. They take advantage of a nonlinear coupling regime that appears when a fast rotating magnetic field is applied to a superparamagnetic bead immersed in a viscous fluid. In this work, we present the development of the technique and we compare it with other techniques capable of measuring the torque applied to the DNA molecule. In this proof of principle, we use standard electromagnets to achieve our experiments. Despite technical difficulties related to the present implementation of these electromagnets, the agreement of measurements with previous experiments is remarkable. Finally, we propose a simple way to modify the experimental design of electromagnets that should bring the performances of the device to a competitive level.     

Damage identification by multi-model updating in the modal and in the time domain

Computational model updating techniques are used to adjust selected parameters of finite element models in order to make the models compatible with experimental data. This is done by minimizing the differences (residuals) of analytical and experimental data, for example, natural frequencies and mode shapes by numerical optimization procedures. For a long-time updating techniques have also been investigated with regard to their ability to localize and quantify structural damage. The success of such an approach is mainly governed by the quality of the damage model and its ability to describe the structural property changes due to damage in a physical meaningful way. Our experience has shown that due to unavoidable modelling simplifications and measurement errors the changes of the corresponding damage parameters do not always indicate structural modifications introduced by damage alone but indicate also the existence of other modelling uncertainties which may be distributed all over the structure. This means that there are two types of parameters which have to be distinguished: the damage parameters and the other parameters accounting for general modelling and test data uncertainties. Although these general parameters may be physically meaningless they are necessary to achieve a good fit of the test data and it might happen that they cannot be distinguished from the damage parameters. For complex industrial structures it is seldom possible to generate unique structural models covering all possible damage scenarios so that one has to expect, that the parameters introduced for describing the damage will not be fully consistent with the physical reality. Even then the change of such parameters identified from test data taken continuously or temporarily over the time may serve as a feature for structural health monitoring. It is well known that low-frequency modal test data or static response data are not very well suited for detecting and quantifying localized small size damage. Time domain response data from impact tests carry high-frequency information which usually is lost when experimental modal data are utilized for damage identification. Even so only little literature was found addressing the utilization of experimental time histories for model updating in conjunction with damage identification.In the present paper we summarize the methodology of computational model updating and report about our experience with damage identification using two different model updating techniques. The first is based on classical modal residuals (natural frequencies and mode shapes) which is extended to allow for simultaneous updating of two models, one for the initial undamaged structure and the second for the damaged structure using the test data of both states (multi-model updating). The second technique uses residuals composed of measured and analytical time histories. Time histories have the advantage of carrying high-frequency information which is beneficial for the detection of local damage and which usually is lost when modal residuals are used. Both techniques have been applied to the same beam structure consisting of two thin face sheets which were bonded together by an adhesive layer. It was the aim of this application to study the performance of the two techniques to localize and quantify the damage which was introduced locally in the adhesive layer.     

Diamagnetic loop measurement in Korea Superconducting Tokamak Advanced Research machine

Diamagnetic loop (DL), which consists of two poloidal loops inside the vacuum vessel, is used to measure the diamagnetic flux during a plasma discharge in the Korea Superconducting Tokamak Advanced Research (KSTAR) machine. The vacuum fluxes in the DL signal can be compensated up to 0.1 mWb by using the coefficients, which are obtained from experimental investigations, in the vacuum flux measurements during vacuum shots under same operational conditions of magnetic coils for plasma experiment in the KSTAR machine. The maximum error in the diamagnetic flux measurement due to the errors of the coefficients was estimated as ～0.22 mWb. From the diamagnetic flux measurements for the ohmically heated circular plasmas in the KSTAR machine, the stored energy agrees well with the estimated kinetic energy within the discrepancy of 25%. When the electron cyclotron heating, the neutral beam injection, and the ion cyclotron resonance heating are added to the ohmically heated limiter plasmas, the additional heating effects can be clearly observed from the increase of the stored energy evaluated in the DL measurement.     

Invited Review Article: Microwave spectroscopy based on scanning thermal microscopy: resolution in the nanometer range

Scanning thermal microscope-detected ferromagnetic resonance (SThM-FMR) combines a thermal near-field microscope with a FMR spectrometer and detects the thermal response due to resonant microwave absorption by measuring the resistivity change in the thermal nanoprobe. The advantage of this technique is to provide imaging capabilities at fixed resonance conditions as well as local microwave spectroscopy at the nanoscale. A technique that uses the same setup but detects the thermoelastic response of the sample is the scanning thermoelastic microscope-detected FMR (SThEM-FMR). This latter technique is advantageous when FMR spectra of single nanostructures have to be recorded at a fixed position. The experimental setups and the signal generation processes of SThM/SThEM-FMR are described in detail. With the SThM-FMR setups a temperature resolution of 1 mK and a local resolution of 30 nm are actually achieved. With SThEM-FMR the obtained local resolution is 10 nm. The detection limits of both techniques can be as low as 10(6) spins. To demonstrate the potential of these new techniques SThM/SThEM-FMR investigations of local magnetic anisotropies, magnetization dynamics of single nanodots and inhomogeneous FMR excitations due to finite size effects are presented. Simultaneously, information on the magnetic parameters, the topography, and the thermal properties is provided. To describe the further potential of this recently developed SThM-FMR technique, combined magnetoresistance and FMR investigations are presented and an outlook on possible future applications is given.     

Volume fraction measurement of dispersoids in a thin foil by parallel energy-loss spectroscopy: development and assessment of the technique

A method to determine the volume fraction of a dispersoid phase based on measurements carried out on thin foils is presented. The method involves the reconstruction of the shape and volume, by electron energy-loss spectroscopy thickness measurements, of the analysed foil and the determination of the volume of the dispersoids using more conventional electron microscopy imaging techniques. Hence the technique does not require the use of stereology theorems. The procedure to measure the total inelastic mean free path and the linearity of its measurement for thicknesses (t) relative to the mean free path (t/λ) up to t/λ ～ 4 is described. A method allowing the conversion of one single experimental λ-value to various collection conditions either graphically or by parameterization is also outlined. Various imaging methods (CTEM, STEM and chemical mapping) were evaluated for their ability to retrieve the distribution of dispersoids and thus their volume. Artefacts of the technique and of the sample preparation method are also discussed. The possibility of applying such techniques using in-column and post-column imaging filters and the limitations of such methods are presented. Although the system has been applied to a relevant metallurgical system in the aluminium industry, it can be used for any other material provided that the values of the mean free path can be obtained.     

High sensitivity magnetometer for measuring the isotropic and anisotropic magnetisation of small samples

We describe how the full, isotropic and anisotropic, magnetisation of samples as small as tens of micrometers in size can be sensitively measured using a piezoresistive microcantilever and a small, moveable ferromagnet. Depending on the position of the ferromagnet, a strong but highly local field gradient of up to ～4200 T/m can be applied at the sample or removed completely during a single measurement. In this way, the magnetic force and torque on the sample can be independently determined without moving the sample or cycling the experimental system. The technique can be used from millikelvin temperatures to ～85 K and in magnetic fields from 2 T to the highest fields available. We demonstrate its application in measurements of the semimagnetic semiconductor Hg(1 - x)Fe(x)Se, where we achieved a moment sensitivity of better than 2.5 × 10(-14) J/T for both isotropic and anisotropic components.     

A combined reflectometry and quartz crystal microbalance with dissipation setup for surface interaction studies

We have developed an instrument for surface interaction studies, which combines a newly invented four detector optical reflectometry setup with quartz crystal microbalance with dissipation (QCM-D) monitoring. The design is such that data from both techniques can be obtained simultaneously on the same sensor surface, with the same signal-to-noise ratio and time resolution, as for the individual techniques. In addition, synchronized information about structural transformations, molecular mass, and the hydration of thin films on solid surfaces can be obtained on the same specimen, as validated by monitoring the formation of supported lipid bilayers on a silica-coated QCM sensor surface. We emphasize that the optical (molecular) mass can be separated from the acoustic mass including hydrodynamically coupled solvent, which means, in turn, that the amount of solvent sensed by the QCM-D technique can be dynamically resolved during adsorption processes. In addition, the advantage/necessity to use four, compared to two, detector reflectometry is emphasized.     

基于信息融合子域适应的不同工况下谐波减速器故障诊断方法

针对工业机器人谐波减速器不同工况数据分布差异大,部分工况数据标签缺失以及单一传感器获取信息不全面,导致 诊断准确率不高的问题,提出一种信息融合子域适应的不同工况下谐波减速器故障诊断方法。 该方法将源域和目标域一维振 动数据利用小波变换构建时频图;使用基于小波变换的图像融合方法整合多个传感器的时频信息并构建融合图像;提出多表示 特征提取结构的改进残差网络以充分挖掘融合样本多表示特征,同时,在无监督场景下将源域和目标域融合样本的多表示特征 进行子域适应处理,减小两域的各个子域间的分布差异,从而将知识从标签丰富的源域迁移到标签缺失的目标域,最终实现不 同工况下谐波减速器的故障诊断。 通过搭建工业机器人谐波减速器故障实验台并进行实测,所提方法在所有迁移任务中平均 准确率可达 98. 8% ,能够有效实现无监督场景中不同工况下谐波减速器的故障诊断。     

Using RHEED to study polytypism

Up to now, relatively few papers have dealt with electron beam investigations of polytypic substances. Recent work in SiC (Gauthier, 1978) pointed out the general interest in the use of reflection high energy electron diffraction (RHEED) for examining well-ordered long-period modifications. The main results are summarized here, showing what information can be obtained from RHEED patterns for the determination of polytype structures and hence possible explanations of growth mechanisms. In the same way, other materials have now been examined by the same technique and some results from zinc sulphide crystals are presented as an illustration. The mixtures of different ZnS modifications are complex; moreover, polytype disorder exists commonly in that substance. Such a situation vindicates the use of other techniques, particularly high resolution electron microscopy.     

Magnetic circular dichroism in electron energy loss spectrometry

The measurement of circular dichroism in the electron microscope is a new, emerging method and, as such, it is subject to constant refinement and improvement. Different ways can be envisaged to record the signal. We present an overview of the key steps in the energy-loss magnetic chiral dichroism (EMCD) experiment as well as a detailed review of the methods used in the intrinsic way where the specimen is used as a beam splitter. Lateral resolution up to 20-30 nm can be achieved, and the use of convergent beam techniques leads to an improved S/N ratio. Dichroic effects are shown for Ni and Co single crystal; as a counterexample, measurements were carried also for a non-magnetic (Ti) sample, where no dichroic effect was found.     

A virtual experiment control and data acquisition system for in situ laser heated diamond anvil cell Raman spectroscopy

Doubled-sided laser heated diamond anvil cell methods allow simultaneous in situ confocal Raman measurements of materials up to megabar pressures and high temperatures. This paper describes a virtual control and data acquisition system developed to automate setups for simultaneous Raman/laser heating experiments. The system enables reduction of experiment time by ～90% in comparison to manual operations, allowing measurements of high quality Raman spectra of even highly reactive or diffusive samples, such as hydrogen at extreme conditions using continuous wave laser heating. These types of measurements are very difficult and often impossible to obtain in a manual operation mode. Complete data archiving and accurate control of various experimental parameters (e.g., on-the-fly temperature determination and self-adjusting data collection time to avoid signal saturation) can be done, and open up possibilities of other types of experiments involving extreme conditions.