Low-temperature magnetic and thermal properties of CePd2In in magnetic fields

A detailed study of the low-temperature magnetization M and specific heat C of CePd₂In is reported. For B 0, M and C show maxima at T_N 1.25 K indicating an antiferromagnetic phase transition as observed previously. In a magnetic field B the transition seen in M is shifted to lower T while T_N as determined from the specific-heat maximum is essentially unaltered up to fields of 6 T. This different behavior is attributed to magnetic anisotropy of the polycrystalline samples. The hyperfine contribution to C is discussed in terms of nuclear quadrupole splitting as well as Zeeman splitting by applied and transferred hyperfine fields. A rough estimate of the Kondo temperature from C sufficiently above T_N yields T_K 1.5 K.     

Thick film resistors in low-temperature resistance thermometry in high magnetic fields

Thick film resistors exhibit a strong dependence on temperature in the cryogenic range below 20 K. In this range the temperature coefficient of resistance is estimated to be comparable to that of commonly used resistance thermometers.The resistance change by the action of the magnetic field is observed to be only small and independent of magnetic field direction. By using these resistors in cryogenic resistance thermometry in intense magnetic field the temperature error due to the magnetoresistance is shown to be only small in comparison with frequently used sensors.According to these results thick film resistors are reported to offer an interesting alternative in cryogenic resistance thermometry within intense magnetic fields.     

Low-temperature strengthening of structural alloys under the action of strong magnetic fields

Results are presented for an experimental study of the effect of strong constant and pulsed magnetic fields on the mechanical properties and deformation features of steels 03Kh20N16AG6, 03KM3AG19, and 12Kh19N10T at temperatures of 293-4.2 K. Relationships are presented connecting the level of critical stresses with magnetic field parameters and the possibility is substantiated of using the low-temperature strengthening effect for steels in determining permissible stresses for structural elements subjected to the effect of strong magnetic fields.Translated from Problemy Prochnosti, No. 6, pp. 48–52, June, 1990.     

Total magnetic fields and read characteristics of infinite length pole piece magnetic recording heads

Magnetic recording head fields generated by current distributions of zero total current flux are calculated considering the two topological possibilities for the current elements being either external to infinite permeability pole pieces or contained entirely within the pole pieces. The frequency response for each of these field configurations is determined by application of the fast Fourier transform.     

Further examinations of carbon/polyesterimide thick-film resistors

A carbon (carbon black and/or graphite)/polyesterimide resin system has been used as a material for polymer thick-film resistors. The physical and chemical properties of this system as a function of curing temperature were evaluated by means of resistance measurements during the curing process, thermogravimetric analysis, adhesion measurements and scanning electron microscopy examinations. The temperature range between 250 and 300 C has been chosen as the most suitable. The basic electrical properties and the resistance stability to low and high temperature shocks and humidity exposure have been evaluated in relation to the conductive filler used in the ink.     

Influence of electrical stress on printed polymer resistors filled with carbon nanomaterials

Superior electrical properties of carbon nanotubes were utilized by the authors in the fabrication of printed resistors. In common applications such as electrodes or sensors, only basic electrical and mechanical properties are investigated, leaving aside other key parameters related to the stability and reliability of particular elements. In this paper we present experimental results on the properties of printed resistive layers. One of the most important issues is their stability under high currents creating excessive thermal stresses. In order to investigate such behavior, a high direct current stress test was performed along with the observation of temperature distribution that allowed us to gain a fundamental insight into the electrical behavior at such operating conditions. These experiments allowed us to observe parametric failure or catastrophic damage that occurred under excessive supply parameters. Electrical parameters of all investigated samples remained stable after applying currents inducing an increase in temperature up to 130 °C and 200 °C. For selected samples, catastrophic failure was observed at the current values inducing temperature above 220 °C and 300 °C but in all cases the failure was related to the damage of PET or alumina substrate. Additional experiments were carried out with short high voltage pulse stresses. Printed resistors filled with nanomaterials sustained similar voltage levels (up to 750 V) without changing their parameters, while commonly used graphite filled polymer resistors changed their resistance value.     

Mechanism of carbon film formation in a discharge with crossed electric and magnetic fields in neon and argon

The process of carbon-film formation in a discharge with crossed electric and magnetic fields in neon and argon has been studied in a system with a cylindrical geometry of electrodes. Radial profiles of the film thickness on an edge substrate have been measured using an interferometric technique. A diffusion model of film formation is proposed, which takes into account the inert gas ion charge exchange and gas heating processes. Experimental data are compared to the results of model calculations.     

Low-temperature magnetic phase transitions of CeBi and CeSb

Specific heat, low- and high-field magnetic susceptibility, thermal expansion, and magnetostriction measurements have been made on single crystals of CeBi and CeSb in order to investigate the low-temperature magnetic phase transitions of these compounds. We have observed structural transitions at the respective Néel temperatures. The maximum tetragonal distortions below T _N are of the order of 10^?3 in both cases. Specific heat results confirm the unusually small overall splitting of the ground-state multiplet. Applications of external magnetic fields induce a variety of interesting effects and provide insight into the magnetic phase diagram of these substances. The results are discussed qualitatively.     

Influence of shape and size on the alignment of multi-wall carbon nanotubes under magnetic fields

The influence of the shape and size of carbon nanotubes (CNTs) on the alignment of multi-wall CNTs was investigated. A CNT suspension with polyethylenimine (PEI) added as a dispersant showed stable dispersion. Stable CNT dispersion had a relatively high zeta potential value compared with poor dispersion. In addition, a strong magnetic field of 12 T was applied to the CNT suspension to investigate the alignment behavior of the CNTs. Good alignment of the CNTs according to the direction of the magnetic field was obtained. The degree of alignment depended on the shape and size of the CNTs, with the thick, straight CNTs showing better alignment than the thin, curved CNTs.     

Synthesis of magnetic fields

The paper deals with some problems of magnetic fields synthesis, depending on determination of the current density distribution, which generates the required magnetic field in the investigated region. Such problems can be reduced to the linear, or nonlinear Fredholm integral equations of the first kind, or to the set of these equations. Fredholm integral equation of the first kind belongs to the class of the ill-posed problems, and for its solving the method of regularisation has been used. In the paper there are given some useful results of synthesis of magnetic fields in few practical configurations.     

On the interaction of magnetic fields and magnetic shields

Some general mathematical expressions have been derived for the induced self and mutual inductances of the wires inside a cylindrical ferromagnetic shell. An application of these results is given. It is shown that the effect of the ferromagnetic shell on the inductances of the multiconducting wires is strongly geometry dependent; the closer the wires to the magnetic shell, the stronger the effect. For wires in the center of the cylinder, no significant result will be caused by the presence of the magnetic shell.     

Calculation of eddy-current-induced magnetic fields in vacuuminterrupters with axial magnetic field contacts

The variation of the nonsteady magnetic-induction field of axially symmetric contact arrangements in space and time is calculated by using a finite-element program system. The influence of individual design elements on the induction field is analyzed and the effectiveness of measures for suppressing eddy current is represented. The delaying and damping effect of the eddy currents on the magnetic field increases from the outside towards the axis of symmetry. This changes the radial field distribution for the duration of the arc and the zone of maximum induction travels towards the inside. When the contacts are open, the radial component predominates over the axial induction field in the vicinity of the contact edge. The azimuthal inherent magnetic field of the arc is free of eddy currents and dominates in the outer arc region, particularly in the phase of current increase     

Low-temperature magnetic properties of HoRh4B4

The low-temperature magnetic properties of HoRh₄B₄ have been studied by means of measurements of the magnetic susceptibility, magnetization, specific heat, thermal expansion, and magnetostriction. The ferromagnetic phase transition at T _M= 6.7 K shows almost ideal S = 1/2 mean field behavior in the specific heat. Crystal field effects due to the splitting of the J = 8 Hund's rule ground state of the Ho³⁺ ions result in Schottky anomalies in the specific heat and the thermal expansion and are also revealed in the low-field magnetic susceptibility and the magnetostriction. Information on the ground state doublet of the 4f electrons has been obtained from the nuclear contribution to the specific heat below 1 K and the high-field magnetization below T_M.This research was supported by the Schweizerische Nationalfonds zur Forderung der wissenschaftlichen Forschung (HRO), by the Department of Energy under Contract No. EY-76-S-03-0034-PA227-3 (LDW, MBM), and by the National Science Foundation under Grant No. NSF/DMR77-08469 (DCJ)