Magnetic pulser and sample holder for time- and spin-resolved photoemission spectroscopy on magnetic materials

A compact coil setup, in conjunction with a high power current pulser, is presented; developed especially for time- and spin-resolved photoemission spectroscopy measuring the sample in magnetic remanence at room temperature. A novel approach is presented where the sample is switched in the stray field of a coil pair. This enables the electrical biasing of the sample without altering the electron trajectories due to field gradients introduced by the coils. The pulser driving the coils reaches a peak power of 1 MW at 1 kA with a switching frequency up to 10 kHz suitable for experiments, for example, with state of the art repetition rates of femtosecond laser systems.     

Construction and development of a time-resolved x-ray magnetic circular dichroism-photoelectron emission microscopy system using femtosecond laser pulses at BL25SU SPring-8

A femtosecond pulsed laser system has been installed at the BL25SU soft x-ray beamline at SPring-8 for time-resolved pump-probe experiments with synchronization of the laser pulses to the circularly polarized x-ray pulses. There are four different apparatuses situated at the beamline; for photoemission spectroscopy, two-dimensional display photoelectron diffraction, x-ray magnetic circular dichroism (XMCD) with electromagnetic coils, and photoelectron emission microscopy (PEEM). All four can be used for time-resolved experiments, and preliminary investigations have been carried out using the PEEM apparatus to observe magnetization dynamics in combination with XMCD. In this article, we describe the details of the stroboscopic pump-probe XMCD-PEEM experiment, and present preliminary data. The repetition rate of the laser pulses is set using a pulse selector to match the single bunches of SPring-8's hybrid filling pattern, which consists of several single bunches and a continuous bunch train. Electrons ejected during the bunch train, which do not provide time-resolved signal, are eliminated by periodically reducing the channel plate voltage using a custom-built power supply. The pulsed laser is used to create 300 ps long magnetic field pulses, which cause magnetic excitations in micron-sized magnetic elements which contain magnetic vortex structures. The observed frequency of the motion is consistent with previously reported observations and simulations.     

Invited article: Vector and Bragg Magneto-optical Kerr effect for the analysis of nanostructured magnetic arrays

Experimental and theoretical aspects of obtaining the magnetic information carried by laser beams diffracted from an array of micro- or nanosized magnetic objects are reviewed. We report on the fundamentals of vector magneto-optic Kerr effect (MOKE), Bragg-MOKE, and second-order effects in the Kerr signal in longitudinal Kerr geometry as well as on an experimental setup used for vector and Bragg-MOKE experiments. The vector and Bragg-MOKE technique in combination with micromagnetic simulation is a reliable tool for measuring the complete magnetization vector and for characterizing the reversal mechanism of lateral magnetic nanostructures. We discuss the Bragg-MOKE effect for three standard domain configurations during the magnetization reversal process and present the expected behavior of the magnetic hysteresis loops.     

大间隙磁力传动系统驱动规律的仿真研究

针对已提出的大间隙行波磁场驱动的磁力传动系统,采用现代计算技术和数值计算中的有限元理论,运用ANSYS软件的磁场分析功能,建立了磁力传动系统的实体模型和有限元模型,通过模拟永磁体的角位移和电磁体线圈的通电状态,对系统工作过程进行了仿真;研究了系统永磁体在转动过程中的受力情况和各参数对系统驱动能力的影响规律,并进行了实验验证。研究结果表明:通过增加线圈匝数、线圈通电电流、永磁体外径和永磁体磁化强度,减小电磁体和永磁体间耦合距离,将电磁体和永磁体的相对位置沿x方向两侧(左侧或右侧)置于5 mm～10 mm范围内等方法,可提高系统的驱动力矩。     

Possibilities of magnetic inspection of plastic deformations preceding failures of low-carbon steels constructions

The possibility of magnetic inspection of plastic deformations preceding the failure of strained steel constructions was studied by locally magnetizing them with an attachable electromagnet. Field dependences of the differential magnetic permeability of a plate made of steel 09Γ2 on the applied and residual stresses were determined. Critical fields of 90° and 180° domain-wall motion at different degrees of deformation were calculated using a model taking into account the contribution of these domain walls to magnetization reversal processes. Dependences of the coercive force and residual magnetization of the plate on the applied and residual stresses, which were measured using a SIMTEST portable magnetic measuring system, are reported.     

大间隙磁力传动系统设计及性能比较

为提高大间隙、高转速条件下磁力传动系统的可靠性,研究了行波磁场驱动的大间隙磁力传动技术.在分析系统主动磁极(电磁体)和从动磁极(永磁体)之间运动状态的基础上,确定了系统电磁体磁极状态切换方法和永磁体运动状态的关系,提出了3种系统驱动方案;基于磁路基本原理,通过磁场分析、系统传递力矩计算模型的建立和系统空间磁场的实验研究,确定了具有较强驱动能力的系统设计方案.     

Decrease in the effect of a gap on coercimetry results when taking the properties of an attachable transducer into account

A method that allows the effect of a gap on the results of coercimetric quality control of articles to be decreased that is based on taking properties of an attachable transducer into account is proposed. The properties of a transducer are taken into account using a preliminary recorded demagnetization line of an attachable electromagnet whose magnetic circuit is not closed by an article. It is shown that the tangential component of the magnetic field of an inspected article during magnetization reversal along this line equals the coercive force of the article if its cross section does not exceed the electromagnet cross section.     

A setup for measuring the magnetic characteristics of soft magnetic materials and articles

An automated setup for measuring the normal magnetization curve, the major and minor magnetic-hysteresis loops, and the main (initial permeability, maximum permeability, residual magnetic induction, induction coercive force, and saturation induction) and additional (the permeability at a field equal to the coercive force, the field strength at which the saturation induction is reached, and the induction at fields equal to the coercive force and the double coercive force) magnetic parameters of soft magnetic materials and articles produced from them is described. Measurements are performed in an open or closed magnetic circuit at a magnetization-reversal frequency of 0.05–0.5 Hz. The block diagram of the setup and its main parameters and characteristics are presented. The operation of the setup and the possibilities of its application are considered.     

Development of effective power supply using electric double layer capacitor for static magnetic field coils in fusion plasma experiments

A cost-effective power supply for static magnetic field coils used in fusion plasma experiments has been developed by application of an electric double layer capacitor (EDLC). A prototype EDLC power supply system was constructed in the form of a series LCR circuit. Coil current of 100 A with flat-top longer than 1 s was successfully supplied to an equilibrium field coil of a fusion plasma experimental apparatus by a single EDLC module with capacitance of 30 F. The present EDLC power supply has revealed sufficient performance for plasma confinement experiments whose discharge duration times are an order of several seconds.     

Experimental setup for laser spectroscopy of molecules in a high magnetic field

An experimental setup to measure the effects of a high magnetic field on the structure and decay dynamics of molecules is designed and constructed. A vacuum chamber is mounted in the bore of a superconducting magnet. A molecular beam passes in the chamber. Pulsed laser light excites the molecules in the field. The parent or fragment ions are extracted by an electric field parallel to the magnetic field. They are detected by a microchannel plate. Their mass and charge are determined by the time-of-flight method. The performance of the setup was examined using resonance-enhanced two-photon ionization through the X(2)?Π-A(2)Σ(+) transition of nitric oxide (NO) molecules. The ions were detected with sufficient mass resolution to discriminate the species in a field of up to 10 T. This is the first experiment to succeed in the mass-selective detection of ions by the time-of-flight method in a high magnetic field. By measuring NO(+) ion current as a function of the laser frequency, the X(2)Π-A(2)?Σ(+) rotational transition lines, separated clearly from the background noise, were observed in fields of up to 10 T. From the relative strengths of the transition lines, the ion detection efficiency was determined as a function of the magnetic field strength. This setup was shown to be applicable in a field higher than 10 T. The Landau levels of molecules were successfully observed to demonstrate the setup.     

基于圆环磁体阵列的线型零磁场系统研究

磁性粒子成像是一种新型示踪剂成像技术,该技术利用磁性粒子在零磁场中的非线性磁化特性对被测物进行成像,其中零磁场的精细度决定其空间分辨率,而零磁场的精细度由空间磁场梯度决定。为了提高空间分辨率,设计了能产生大磁场梯度的静磁场结构,将其与驱动结构组合成线型零磁场系统。首先设计了基于圆环磁体阵列的静磁场结构,利用大梯度的静磁场构造精细线型零磁场;其次设计了基于亥姆霍兹线圈的驱动结构及其驱动方式,确定线型零磁场扫描范围与驱动电流之间的关系;最后计算线型零磁场系统的空间分辨率,研究磁场梯度、粒子粒径与空间分辨率之间的规律性。实验结果表明:基于圆环磁体阵列的静磁场结构产生的磁场梯度为4.804 T/m,当使用30 nm磁性粒子作为示踪剂时,系统的空间分辨率为0.540 mm,此时线型零磁场能在30 mm的范围内对被测物进行平移扫描。证明了基于圆环磁体阵列的线型零磁场系统用于提高磁性粒子成像分辨率的可行性。     

FGZ-8半导体激光治疗机设计与研制

采用二合一光纤系统、高效率光纤耦合装置、Al Ga In P半导体激光器、方便适用的光纤定位装置以及稳定可靠的电源控制系统 ,研制了一种新型 6 5 0 nm半导体激光治疗仪 ,其光纤端输出达 10 9m W。该仪器已在生物医学领域成功应用。     

Miniature pulsed magnet system for synchrotron x-ray measurements

We have developed a versatile experimental apparatus for synchrotron x-ray measurements in pulsed high magnetic fields. The apparatus consists of a double cryostat incorporating a liquid nitrogen bath to cool the miniature pulsed coil and an independent helium flow cryostat allowing sample temperatures from 4 up to 250 K. The high duty cycle miniature pulsed coils can generate up to 38 T. During experiments at 30 T a repetition rate of 6 pulsesmin was routinely reached. Using a 4 kJ power supply, the pulse duration was between 500 mus and 1 ms. The setup was used for nuclear forward scattering measurements on 57Fe up to 25 T on the ESRF beamline ID18. In another experiment, x-ray magnetic circular dichroism was measured up to 30 T on the ESRF energy dispersive beamline ID24.     

Simultaneous measurement of magnetization and magnetostriction in 50 T pulsed high magnetic fields

To simultaneously perform magnetization and magnetostriction measurements in high magnetic fields, a miniaturized device was developed that combines an inductive magnetometer with a capacitive dilatometer and, therefore, it is called "dilamagmeter." This combination of magnetic and magnetoelastic investigations is a new step to a complex understanding of solid state properties. The whole system can be mounted in a 12 mm clear bore of any cryostat usually used in nondestructive pulsed high field magnets. The sensitivity of both methods is about 10(-5) A m(2) for magnetization and 10(-5) relative changes in length for striction measurements. Measurements on a GdSi single crystal, which are corrected by the background signal of the experimental setup, agree well with the results of steady field experiments. All test measurements, which are up until now performed in the temperature range of 4-100 K, confirm the perfect usability and high stability in pulsed fields up to 50 T with a pulse duration of 10 ms.     

Measurements of the transverse susceptibility and magnetization of magnetic fluids

A new method for calculating the magnetization of magnetic fluids and a setup for measuring the transverse magnetic susceptibility as a function of an external bias field are described. The results obtained via the new method and a known sweep method are compared. The presented results of a magnetogranulometric analysis of five samples of a magnetic fluid with different concentrations of the magnetic phase confirm the high accuracy of the new technique.     

基于磁场三维动态导磁球上的磁性液体行为研究

利用自行搭建的磁场三维动态展示装置,通过调控电磁铁的励磁电流,进行磁场三维动态实心导磁球上磁性液体的行为研究。观察实心导磁球处于不同磁场下,三维立体磁感线的展示效果及其磁性液体突起三维尖峰的数目、间距、高度,探索分析这些参数与磁场间的变化规律,以期进一步拓展磁性液体的应用。     

First-order reversal curves acquired by a high precision ac induction magnetometer

We present a setup allowing to characterize the local irreversible behavior of soft magnetic samples. It is achieved by modifying a conventional ac induction magnetometer in order to measure first-order reversal curves (FORCs), a magnetostatic characterization technique. The required modifications were performed on a home-made setup allowing high precision measurement, with sensibility less than 0.005 Oe for the applied field and 10(-6) emu for the magnetization. The main crucial point for the FORCs accuracy is the constancy of the applied field sweep rate, because of the magnetic viscosity. Therefore, instead of the common way to work at constant frequency, each FORC is acquired at a slightly different frequency, in order to keep the field variation constant in time. The obtained results exhibit the consequences of magnetic viscosity, thus opening up the path of studying this phenomenon for soft magnetic materials.     

Effect of a gap in the electromagnet-object magnetic circuit on the magnetic field of surface flaws in different steels

The dependences of the magnetic-field strength of surface flaws in various steels on the electromagnet current have been studied for different gaps in the magnetic circuit. It is shown that an anomalous ratio of the magnetic-field strengths of flaws in hard and soft magnetic materials holds in the entire range of gap changes. The dependence of the ratio of the magnetic-field strengths of a flaw, which are obtained for different gaps in the magnetic circuit, on the electromagnet current has an extremum in the region of weak currents and, at high currents, tends toward to a constant value, which is determined by the value of the set gaps. The results are considered, taking their interrelations with the magnetic properties of materials and processes of their magnetization in the presence of a demagnetization factor into account.     

The topography of the field and flux inside and above the surfaces of ferromagnetic plates during their contact and contactless magnetization

Modeling and experimental studies of the spatial distributions of the field and flux inside and above the surface of ferromagnetic plates of different dimension types, which were locally magnetized by U-shaped electromagnets, were performed. It was established that the location of a magnetic inhomogeneity in the interpole zone of an electromagnet substantially affects the results of a local measurement of the coercive force using a demagnetization current. It is shown that the presence of a gap in the magnetic circuit impairs the magnetization of the interpole zone of an object to a higher degree than the magnetization of the near-pole zone. Recommendations on the concentration of the magnetic flux in the interpole zone via a decrease in the interpole distance of the electromagnet are given. Possible locations of internal-field probes that provide local measurements of the magnetic properties of a substance are determined.     

Quantitative measurements of magnetic stray field dynamics of Permalloy particles in a photoemission electron microscopy

By example of a Permalloy particle (40 × 40 μm(2) size, 30 nm thickness) we demonstrate a procedure to quantitatively investigate the dynamics of magnetic stray fields during ultrafast magnetization reversal. The measurements have been performed in a time-resolving photoemission electron microscope using the X-ray magnetic circular dichroism. In the particle under investigation, we have observed a flux-closure-dominated magnetic ground structure, minimizing the magnetic stray field outside the sample. A fast magnetic field pulse introduced changes in the micromagnetic structure accompanied with an incomplete flux closure. As a result, stray fields arise along the edges of domains, which cause a change of contrast and an image deformation of the particles geometry (curvature of its edge). The magnetic stray fields are calculated from a deformation of the X-ray magnetic circular dichroism (XMCD) images taken after the magnetic field pulse in a 1 ns interval. These measurements reveal a decrease of magnetic stray fields with time. An estimate of the lower limit of the domain wall velocity yields about 2 × 10(3) m s(-1).