The effect of a weak magnetic field on the mobility of dislocations in silicon

The magnetoplastic effect in dislocation silicon is discovered. It is shown that in the presence of tensile stresses (up to 20 MPa), the mechanically activated path of surface dislocation half-loops is limited mainly by the dynamics of defects in various slip systems relative to the applied load. The activation barriers for the motion of dislocations controlled by various conditions in the temperature range T=850–950 K are E _aF=2.1±0.1 eV and E _aS=1.8±0.1 eV. An increase in the path of surface dislocation half-loops and a change in the activation barriers are detected (E _aF=1.4±0.1 eV and E _aS=1.6±0.1 eV) after subjecting silicon to a magnetic field (B=0.7 T) for 30 min. Possible reasons behind the observed effects are discussed.     

The starting stress for dislocations in a superlattice

The forces on superdislocations due to the state of the antiphase boundaries (APB) are examined as functions of temperature and concentration on the basis of a previously expounded theory of component concentrations and degree of order at APB in superlattices of CsCl type. Forces due to loss of position correlation in the glide plane are also examined. It is considered that the yield points of superlattices as functions of concentration may be explained by these mechanisms.     

On the magnetic properties of dislocations in silicon

The anisotropy of a group of equidistant lines in the EPR spectrum of plastically deformed Si can be described as line splitting in a nearly axial crystal field, the axis being parallel to the Burgers vector of the dislocations. We suppose that the spins of the unpaired electrons in the core of the 60° dislocations are coupled along limited segments giving rise to superparamagnetic resonance.     

Optical method for measurement of magnetophoretic mobility of individual magnetic microspheres in defined magnetic field

The magnetophoretic mobility of magnetic microspheres, nanospheres and particles depends not only on type and amount of encapsulated magnetic compound, but also on microsphere-internal distribution, solvent system, porosity and other factors. Using a microscopic setup with automated digital image processing, different magnetic microspheres were investigated for size, acceleration and velocity of each single microsphere in the suspension. The overall magnetophoretic mobility (responsiveness to an external magnetic field) was not directly proportional to the saturation magnetization of the magnetic microspheres.     

In situ investigation of the effect of a magnetic field on the mobility of dislocations in deformed KCl:Ca single crystals

This paper presents the results of an experimental investigation into the mobility of edge dislocations in KCl:Ca single crystals and the effect of a static magnetic field of 0.3 T on the dislocation mobility. The experiments on the effect of a magnetic field on the dislocation mobility were carried out with the use of a high-resolution (1 ms) method that permits in situ measurements of the sample dipole moment induced by the motion of charged dislocations as the crystal is being deformed. It is found that the starting stress is reduced in a magnetic field and the activation volume for overcoming of point defects by the dislocations is increased. It is further found that the magnetic field increases the rate of motion of the dislocations at the initial stage of deformation (to the point of dislocation multiplication) but has no effect on the mobility in the multiplication stage. Fiz. Tverd. Tela (St. Petersburg) 39, 630–633 (April 1997)     

Redistribution of dislocations in silicon near stress concentrators

The distribution of defects in dislocation tracks in silicon plates was studied for various indentation angles. The regularities of variations in the linear density and maximum path of dislocations in slip bands are established. A model is proposed to describe the distribution of dislocations in the dislocation tracks. By fitting the theory to the experimental data, the dependence of this distribution on the energy relaxation time is determined.     

Effect of magnetic field on tempering processes in silicon iron

The effect of magnetic fied on the annealing of silicon iron (3% Si) was studied in the temperature range 480–680°C. The imposition of a magnetic field at 480°C leads to more complete tempering by comparison with similar annealing without field. The effect of the magnetic field on the primary recrystallization texture of the silicon iron is shown: this is expressed in the enhanced scattering of deformation type orientations in the annealing texture.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 82–87, January, 1973.     

Sharp increase in mobility of spiral dislocations by a pulsed electric field

An investigation is made of the change in expansion rate V of spiral dislocational half-loops in NaCl crystals after brief application of an electric field. It is established that, after the application of a field pulse at fixed shear stress, V rises sharply at first and then, with time, falls exponentially to its initial value. The initial increase in V depends on the amplitude of the electric pulse, and the relaxation time of its subsequent fall on the temperature. The activation energy of the process is determined from the temperature dependence of the relaxation time.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 71–74, March, 1979.     

Electrically stimulated motion of dislocations in a constant magnetic field

This paper reports on the results of investigations into the dislocation mobility in n-Si single crystals (N _d =5×10²⁴ m^?3) upon simultaneous exposure to electric (j=3×10⁵ A/m²) and magnetic (B≤1 T) fields. It is found that the introduction of dislocations (≈10⁹ m^?2) into dislocation-free silicon doped with phosphorus leads to the appearance of the paramagnetic component of the magnetic susceptibility. The paramagnetic component increases with an increase in the dopant concentration. Similar transformations in silicon account for the formation of magnetically sensitive impurity stoppers that respond to external magnetic perturbations. An analysis of the behavior of dislocations in electric and magnetic fields has revealed a parabolic dependence of the dislocation path length on the magnetic induction B. The effective charges and mobilities of dislocations are numerically calculated from the results obtained. A model is proposed according to which the observed increase in the dislocation mobility is associated with the decrease in the retarding power of magnetically sensitive stoppers due to a local change in the magnetic characteristics of the material and the spin-dependent reactions stimulated by a magnetic field.     

Effect of magnetic field on the terahertz radiationdetection in high electron mobility transistors

In this paper, we make a theoretical investigation of the plasma-wave instability mechanism in a two-dimensional electron fluid in a high electron mobility transistor (HEMT) driven by the terahertz radiation in the presence of a perpendicular magnetic field. It is found that the resonant peaks of the gate-to-source/drain admittances and detection responsivity depend on the strength of the external magnetic field. Such phenomena can be used to produce a desired effect by adjusting the intensity of the magnetic field.     

Behavior of dislocations in silicon in the presence of mechanical and magnetic perturbations

Various types of dislocation stoppers are identified and their basic parameters are determined. Using dislocation loops as an example, the effect of internal stresses on the motion of linear defects in n-and p-Si in the field of external elastic forces is estimated. It is found that preliminary magnetic treatment of silicon plates activates the dislocation transport. In the absence of external mechanical loads, displacement of dislocation half-loops (30–50 μm) in the nonuniform field of internal stresses in a silicon crystal with a scratch (stress concentrator) is detected experimentally during isothermal annealing for 0.5–3 h at a temperature of 600–700°C. Dislocation transport is described taking into account the intrinsic (lattice) potential barrier of the crystal and two types of stoppers on the basis of magnetosensitive point defects (dopant) and “forest” dislocations. A kinetic model is proposed for describing the magnetostimulated variation of the mobility of linear defects associated with the formation of long-lived complexes with a paramagnetic impurity. It is found experimentally that the velocity of dislocations in n-and p-Si increases by a factor of 2 and 3, respectively, upon treatment of the semiconductor in a magnetic field B=1 T for 5–45 min. The “magnetic memory” effect in silicon containing dislocations is detected and kinetic aspects of the effect under natural conditions of sample storage after the removal of the magnetic field are considered. Partial velocities of dislocations and their delay times at various types of stoppers are calculated from the matching of experiment with theory.     

Effect of a constant magnetic field and a pulse electric current on the mean linear density of twinning dislocations in bismuth crystals

Bismuth crystals are studied under the joint action of a pulse electric current and a constant magnetic field. It is shown that the combined effect of a constant magnetic field and pulse current leads to a substantial decrease in the mean linear density of twinning dislocations piled up at the boundaries of wedge twins. The decrease in the mean linear density of twinning dislocations is accompanied by a decrease in the microhardness of the samples.     

Effect of a magnetic field on the flow stress of Co and Fe single crystals

In a range of plastic deformation, the flow stress drop and the stress relaxation of Co and Fe single crystals are observed under an a.c. magnetic field. The magnitude of these drops is discussed on the basis of different deformation modes due to the crystal structure.     

Effect of the induced magnetic field on peristaltic flow of a couple stress fluid

We have analyzed the MHD flow of a conducting couple stress fluid in a slit channel with rhythmically contracting walls. In this analysis we are taking into account the induced magnetic field. Analytical expressions for the stream function, the magnetic force function, the axial pressure gradient, the axial induced magnetic field and the distribution of the current density across the channel are obtained using long wavelength approximation. The results for the pressure rise, the frictional force per wave length, the axial induced magnetic field and distribution of the current density across the channel have been computed numerically and the results were studied for various values of the physical parameters of interest, such as the couple stress parameter γ, the Hartmann number M, the magnetic Reynolds number Rm and the time averaged mean flow rate θ. Contour plots for the stream and magnetic force functions are obtained and the trapping phenomena for the flow field is discussed.     

Effect of ultrasonic treatment on the mobility of short dislocations in Si crystals

The effect of ultrasonic treatment on the mobility of short surface dislocations in Si crystals is investigated. It is found that ultrasonic treatment of Si crystals changes the velocity of dislocations under a permanent mechanical load. The nature of variation of dislocation velocity is determined by the sign of external stresses acting on the sample: compressive forces decrease while tensile forces increase the velocity of dislocations. After ultrasonic treatment of the samples, a decrease in the activation energy for dislocation motion and the enhancement of the electroplastic effect are observed. A possible mechanism of the observed effects is considered.     

Effect of pulsed magnetic field annealing on the microstructure and texture of grain-oriented silicon steel

The effect of pulsed magnetic primary annealing on the microstructure and texture of two-stage cold-rolled silicon steel is investigated. Specimens are annealed at 700 °C for 1 h under a 1 T pulsed magnetic field along different directions with respect to the sample coordinate system. Crystallographic orientation and grain size are identified by analyzing electron backscattered diffraction pattern. The effects of magnetic field treatment are related to the magnetic field direction. Based on the anisotropy energy of ferromagnetic material during magnetic annealing, a hypothesis is proposed. All of the experimental results in this work support the proposed model.