The μSR setup on the muon beam of the synchrocyclotron at the Konstantinov Institute of Nuclear Physics

The μSR setup for investigating the distribution of magnetic fields in solids using the muon spin rotation (μSR) method is described. The setup is characterized by a high degree of homogeneity of the magnetic field at the site of the sample under investigation, compensation of scattered magnetic fields to a level of ?10^?2 G, and a time resolution of 2.5 ns (the full width at half-maximum). The setup is suitable for μSR measurements on samples in the temperature range of 5–300 K with a precision of ±0.1 K.     

LD外腔结构的传输矩阵理论分析

利用传输矩阵理论结合具体实验装置分析了外腔反馈注入系统的特性和反馈注入光束的传输特点。对准直型和会聚型两种不同的外腔结构分别进行了理论计算和比较,得出了会聚型外腔具有对外腔镜倾斜失调不灵敏的突出优点的结论。并在半导体激光器列阵的外腔实验研究中获得上述理论的验证,得到了远场分布光瓣宽度(FWHM)为0.46°,相应于光束质量为1.12倍衍射极限的激光输出。     

An automatic setup for measuring low-field temperature dependencies of magnetoresistances of film samples

A simple method for magnetoresistance measurements in weak fields based on using a low-frequency alternating magnetic field is proposed. The special feature of this method is the direct measurement of the difference in resistance ΔR of the sample under study in the field and in the absence of the field, which offers a chance to significantly increase measurement sensitivity. The automatic setup for measuring temperature dependencies of magnetoresistance of film metallic samples with a ΔR sensitivity of up to 10^?7 Ω is described. The temperature dependencies of magnetoresistance of thin-film nanocrystalline Co-Cu alloy samples in weak magnetic fields and in a temperature range of 77–300 K are studied.     

In-line holographic electron microscopy in the presence of external magnetic fields

It is now a well-known fact that the phase of electron waves is altered by external magnetic fields via the Aharonov-Bohm effect. This implies that any electron interference effects will be to some degree affected by the presence of such fields. In this study we examine the distortion effects of external (constant and variable) magnetic fields on electron interference and holography. For digital holography, the reconstruction of the object is done via numerical calculations and this leaves the door open for correcting phase distortions in the hologram reconstruction. We design and quantitatively assess such correction schemes, which decidedly depend on our knowledge of the magnetic field values in the holographic recording process. For constant fields of known value we are able to correct for magnetic distortions to a great extent. We find that variable fields are more destructive to the holographic process than constant fields. We define two criteria, related respectively to global and local contrast of the hologram to establish the maximum allowed external field which does not significantly hinder the accuracy of in-line holographic microscopy with electrons.     

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.     

Torque detected broad band electron spin resonance

We present a novel technique to measure high frequency electron spin resonance spectra in a broad frequency range (30-1440 GHz) with high sensitivity. We use a quasioptical setup with tunable frequency sources to induce magnetic resonance transitions. These transitions are detected by measuring the change in the magnetic torque signal by means of cantilever torque magnetometry. The setup allows tuning of the frequency, magnetic field, polarization, and the angle between the sample and the external magnetic field. We demonstrate the capabilities of this technique by showing preliminary results obtained on a single crystal of an Fe(4) molecular nanomagnet.     

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.     

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.     

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.     

Compact magnetospectrometer for pulsed magnets based on infrared quantum cascade lasers

In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated via cyclotron-resonance studies under pulsed magnetic fields up to 60 T.     

Experimental setup for investigating topochemical transformations of ferromagnetic nanoparticles

An experimental setup controlling the topochemical transformations in synthesis of ferromagnetic metal nanoparticles is described. The setup is based on a vibrating magnetometer. The range of operating temperatures in the reaction zone is 300–870 K. The required sensitivity is maintained by a magnetic field of up to 0.6 T. Gases (or gas mixtures) may be blown through the reactor at a flow rate as high as 150 cm³/min. The experimental results illustrating the capabilities of the setup are presented.     

Development of an improved Kelvin probe force microscope for accurate local potential measurements on biased electronic devices

An improved setup for accurate near‐field surface potential measurements and characterisation of biased electronic devices using the Kelvin Probe method has been developed. Using an external voltage source synchronised with the raster‐scan of the KPFM‐AM, this setup allows to avoid potential measurement errors of the conventional Kelvin Probe Force Microscopy in the case of in situ measurements on biased electronic devices. This improved KPFM‐AM setup has been tested on silicon‐based devices and organic semiconductor‐based devices such as organic field effect transistors (OFETs), showing differences up to 25% compared to the standard KPFM‐AM lift‐mode measurement method.     

Precision Measurements and Compensation for the Transverse Components of the Solenoids' Magnetic Field

A device developed at the Budker Institute of Nuclear Physics (BINP) to measure with a high precision the direction of the magnetic field lines in the vicinity of the solenoid axis is described. The transverse field components are automatically measured by a small (<15 cm³ in volume) compass-based sensor during its motion along the axis. The sensor's absolute sensitivity is ～0.1–0.9 mG and is limited only by external vibration noise. The upper bound of this range (～1 G) is governed by the current in the circuits producing the fields that compensate for the local misalignments of the field lines. The capabilities of the device are illustrated by the results from adjusting the solenoid fields in electron coolers recently built by the BINP. The procedures used to do this are described. The feasibility of obtaining the highest-quality field is shown. For one plant with a field intensity of ～1 kG, the rms deviation of the field lines from the axis is <10^?5 rad within a length of 3 m.     

Superconducting quantum interference device setup for magnetoelectric measurements

A commercial superconducting quantum interference device (SQUID) setup (MPMS 5S from Quantum Design), equipped with a magnetic ac susceptibility option, is modified for measurements of the linear magnetoelectric (ME) effect, i.e., of the magnetic moment induced by an applied external electric field in a ME sample. Test measurements on a Cr(2)O(3) (111) single crystal are in excellent agreement with previously reported data of its ME susceptibility. The main advantages of the proposed setup are the improved precision due to the high sensitivity of the SQUID magnetometer in combination with the lock-in technique and a relatively simple experimental realization.     

Precision field averaging NMR magnetometer for low and high fields, using flowing water

The separated oscillatory field magnetic resonance technique (Ramsey technique) has been employed with flowing water as a volume averaging magnetometer. Polarization and detection were performed in high fields, external to the volume over which the magnetic field was to be averaged. An accuracy of a few parts in 10(7) at a nominal field of 18 G was obtained. The technique is applicable, using standard equipment, for the measurement of fields ranging from kilogauss down to milligauss.     

Theoretical study of field emission by a four atoms nanotip: implications for carbon nanotubes observation

A fully three-dimensional quantum model is developed to simulate the emission of electrons by a nanotip in applied fields ranging from 0.4 to 0.8 V/A and their diffusion by an extended molecule. It is shown that the widening of the beam, when the applied field is increased, can be attributed to an increase in the number of emitting atoms. Simulated images of a (9,0) carbon nanotube, in a Fresnel projection microscope-type setup, for various applied fields, reproduce the experimental, so-called, "sucking-in" effect. The relationship between this effect and the transmission probability of the nanotube is studied.     

Development and application of setup for ac magnetic field in neutron scattering experiments

We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.     

Exposure of biological preparations to radiofrequency electromagnetic fields under low gravity

There is interest as to whether the electromagnetic fields used in mobile radiotelephony might affect biological processes. Other weak fields such as gravity intervene in a number of physical and biological processes. Under appropriate in vitro conditions, the macroscopic self-organization of microtubules, a major cellular component, is triggered by gravity. We wished to investigate whether self-organization might also be affected by radiotelephone electromagnetic fields. Detecting a possible effect requires removing the obscuring effects triggered by gravity. A simple manner of doing this is by rotating the sample about the horizontal. However, if the external field does not also rotate with the sample, its possible effect might also be averaged down by rotation. Here, we describe an apparatus in which both the sample and an applied radiofrequency electromagnetic field (1.8 GHz) are stationary with respect to one another while undergoing horizontal rotation. The electromagnetic field profile within the apparatus has been measured and the apparatus tested by reproducing the in vitro behavior of microtubule preparations under conditions of weightlessness. Specific adsorption rates of electromagnetic energy within a sample are measured from the initial temperature rise the incident field causes. The apparatus can be readily adapted to expose samples to various other external fields and factors under conditions of weightlessness.     

PIV measurements of air-core intake vortices

Particle Image Velocimetry (PIV) measurements were conducted in a large-scale hydraulic model to obtain the horizontal velocity field of intake vortices with considerable air entrainment. Vortex wandering and air-core diameter were determined by object detection using PIV images and velocity vector maps. This allowed for the calculation of ensemble- and azimuthally-averaged velocity fields. The results of the horizontal velocity field around the vortex, whose circulation affects a wide area, confirm the applicability of the analytic solution of the 2D Navier–Stokes equation for a potential (free) vortex. The setup and the improvement of the PIV measurements and their limitations are presented. For example, a completely resolved velocity field close to the air-core did not exist due to reflections at the interface between air and water. Vortex characteristics like vorticity and circulation are derived from the velocity fields and turbulence is shown by representing in-plane Turbulent Kinetic Energy (TKE).     

An automated setup for investigation of anisotropy of the Gruneisen parameter of solids in the temperature range 77–350 K using the photoacoustic technique

An automated setup for studying the anisotropy of the Gruneisen parameter of solids in the temperature range 77–350 K using the photoacoustic technique is described. The serviceability of the setup was tested at low (77–300 K) and high (300–350 K) temperatures on strontium titanate and triglycine sulphate single crystals, respectively.