Magnetic-field induced generation of A-like centers in Cz-Si crystals

The effect of the constant magnetic-field induced generation of oxygen–vacancy defects in Czochralski-grown silicon crystals was detected for the first time. The qualitative theory of the effect is given. It assumes that the effect arises from excitation of the Si–O bond of interstitial oxygen and is valid for both constant and pulsed magnetic fields. Experimental verification of the theory in the combined constant and pulsed fields strongly confirmed it.     

Magnetosensitive defects generated during plastic straining of NaCl:Eu crystals

The excitation of an equilibrium subsystem of point defects in plastically strained NaCl:Eu crystals has been studied. It is established that the macroplastic straining of crystals containing three-dimensional EuCl₂ precipitates leads to a decrease in the amount of these precipitates, accompanied by the appearance of new emission centers of two types. In the easy glide stage, the plastic straining is additionally accompanied by a decrease in the fraction of flat EuCl₂ precipitates and an increase in the content of nonequilibrium small-size complexes of impurity-vacancy dipoles sensitive to an external magnetic field. In thoroughly annealed crystals with the point defect subsystem in a nearly equilibrium state, individual dislocations exhibit displacement caused by the action of a pulsed magnetic field and by the joint action of constant and microwave magnetic fields under the electron paramagnetic resonance conditions.     

Ferromagnetism in defective yttria-stabilized zirconia

Significant research attention has been devoted to identifying and synthesizing new magnetic materials via doping of non-magnetic materials. The material defects offer an approach to stabilize ferromagnetism in non-magnetic materials such as oxygen-deficient HfO₂ and oxygen-deficient ZrO₂. In this study, we demonstrated room-temperature ferromagnetism via nitrogen ion implantation on yttria-stabilized zirconia (YSZ) single crystals. The results of structural and chemical analyses indicate the formation of a distinct surface layer through the implantation of nitrogen ions and potential oxygen vacancies. The lattice constant in this surface layer increased by 0.6% compared to the bulk value. Nitrogen ions were observed in this region, and their concentration was estimated to be 2.32 atoms per unit cell. In contrast to the lack of magnetic hysteresis in a YSZ single crystal, ferromagnetic hysteresis was observed in the ion-implanted YSZ crystals, owing to defects—nitrogen ions and oxygen vacancies in the surface layer.     

Simulation of the structure of oxygen hole centers in Mg2SiO4 and Mg2SiO4: Cr forsterite crystals by the interatomic potential method

The structure of oxygen hole centers in forsterite crystals has been simulated using the interatomic potential method. The energies of isolated oxygen hole centers, as well as the energies of their clusters with intrinsic and extrinsic defects of the crystal, have been estimated for different arrangements of point defects in the structure. It has been shown that the most energetically favorable position for isolated oxygen hole centers is the O3 position, in which the gain in the formation energy is equal to 0.17 eV as compared to the O2 position and 1.66 eV as compared to the O1 position. The maximum energy gain due to the association energy can be achieved when the oxygen hole centers are located at the vertices of the tetrahedron with a silicon vacancy. The presence of chromium in the forsterite crystal can increase the probability of the formation of silicon vacancies. The obtained results have been discussed in terms of the experimental investigations of the color centers generated in the Mg₂SiO₄ and Mg₂SiO₄: Cr crystals under ionizing radiation.     

Broadening of paramagnetic resonance lines by charged point defects in neodymium-doped scheelites

We study paramagnetic resonance linewidth in a series of CaWO₄ and CaMoO₄ crystals with different concentrations of neodymium ions (0.0031–0.81 at %). Experimental data are interpreted in the framework of the statistical theory of line broadening by charged point defects. In our calculations, three different contributions are singled out: arising from the local electric fields, electric field gradients and magnetic fields of the nearby point defects. The interaction parameters are determined from the spectroscopic data available for Nd:CaWO₄ crystal. Direct calculations of the linewidth are performed for different crystal orientations with respect to external magnetic field. We conclude that major contribution to the broadening comes from the interactions with random electric fields produced by neodymium and charge compensator ions.     

Effect of a pulsed magnetic field on the real solid-solution structure in the Sb-As system

A first study of the effect of weak pulsed magnetic fields (PMFs) on Sb_1?xAs_x solid solution crystals is reported. An effect of long-time (months) redistribution of the solid solution components at room temperature after a short (seconds) exposure to a PMF was revealed. The effect includes stages of enrichment of the crystal surface in antimony with the formation of clusters, antimony cluster breakup, and a decrease in surface antimony content, which is accompanied by a substantial improvement in solid-solution homogeneity. The PMF-induced component redistribution entails a decrease in the crystal melting temperature. Rupture of stressed chemical bonds in arsenic vacancy complexes, which is induced by a change in their multiplicity under PMF exposure, is considered as a possible trigger mechanism.     

Microwave absorption spectra and the problem of the crystal field in tetragonal compounds HoBa2Cu3O x (x = 6.0, 6.3)

The resonance microwave absorption at wavelengths 871, 406, 305, and 118 μm in tetragonal layered perovskites HoBa₂Cu₃O _x (x = 6.0, 6.3) in pulsed magnetic fields up to 40 T has been detected. This absorption is caused by the electronic transitions between low lying levels of the Ho³⁺ ion in the crystal field. The positions and intensities of the basic resonance absorption lines for the crystal with x = 6.0 in the magnetic field oriented along the tetragonal axes are adequately described in terms of the tetragonal crystal field with known interaction parameters. To explain the weaker absorption lines, it is necessary to take into account the effect of the inhomogeneous orthorhombic and monoclinic components of the crystal field, which are due to disorder in the oxygen subsystem. This effect is more pronounced in the absorption spectra of the crystal with x = 6.3 for which the oxygen disorder is more pronounced.     

Magnetoplastic effects in solids

This paper is an overview of the studies into the effect of weak magnetic fields on the structure and mechanical properties of nonmagnetic solids of various nature (ionic, covalent, molecular, and metallic crystals, polymers, etc.). The various effects and aftereffects initiated by static, pulsed, and microwave magnetic fields that have been discovered over the past 15 years are classified and critically analyzed. The thermodynamic and kinetic aspects of the magnetic-field sensitivity of real solids with structural defects containing paramagnetic centers (electrons, holes, radicals, excitons, etc.) are discussed. Possible mechanisms for the effect of a weak magnetic field on the defect structure of crystals are considered. Special attention is given to the most developed chemical-physical theory of spin-dependent reactions between mobile particles and unpaired electrons. Interpretation of magnetoplastic effects is proposed in terms of the spin, electron, molecular, and dislocation dynamics of the complex multistage processes initiated by a magnetic field in a system of metastable structural defects.     

Formation of elementary radiation defects in halide crystals with different types of crystal lattice

Pulsed spectrometry with time resolution has been used to study processes for creation of self-localized excitons and F centers under the action of a pulsed electron flux of nanosecond duration at temperatures in the region from 80 to 600 K in CaF₂ and LiF crystals. It is shown that an alternative to creation of self-localized excitons in the triplet state with increased crystal temperature during irradiation is formation of an F-H pair. A comparative analysis of the effectiveness of the processes for creation of elementary defects in the crystals studied is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 13–19, January, 1995.     

1H NMR study of static and fluctuating internal Magnetic fields in Tb(C2H5SO4)3 · 9 H2O ising ferromagnet

The pulsed NMR method is applied to an analysis of a complicated structure of inhomogeneous internal fields in a ferromagnetic crystal. Proton magnetic resonance in the Ising ferromagnet TbES at a temperature range from 1.6 K down to 35 mK is studied at frequencies of 10–35 MHz. A complicated picture of static and fluctuating internal magnetic fields in the crystal is presented. Interatomic distances are shown to have an uncertainty of the order of 0.2% due to defects in the crystal lattice. The fluctuations of internal magnetic fields produced by thermal excitation and spin-spin relaxation of Tb³⁺ ions give rise to the effective nuclear magnetic relaxation: 1/T₁₍₂₎～exp (δ/kT), where δ is the energy splitting of the lowest Tb³⁺ quasi-doublet. The rate of these fluctuations in TbES at low temperatures is approximately equal to 2×10⁷ s^?1 being independent of temperature and magnetic field.     

Effect of heat treatment on electronic phase in underdoped La2-xSrxCuO4 single crystal

Superconducting La1.937Sr0.063CuO4 crystals grown by the travelling-solvent floating-zone technique were thermally treated under various temperatures and oxygen pressures for moderately adjusting the oxygen content. The response of intrinsic electronic property of the crystals to the change of hole density in La2-xSrxCuO4 in the vicinity of the magic doping of x= 1/16 （= 0.0625） is studied in detail by magnetic measurements under various fields up to 1 T. It is found that when the superconducting critical temperature （Tc） increases with the oxygen content, there appears also a new subtle electronic state that can be detected from the differential curves of diamagnetic susceptibility dx/dT of the crystal sample. In contrast with the intrinsic state, the new subtle electronic state is very fragile under the magnetic fields. Our results indicate that a moderate change in oxygen doping does not significantly modify the intrinsic electronic state originally existing at the magic doping level.     

Effect of a weak magnetic field on the state of structural defects and the plasticity of ionic crystals

The aim of this work is to examine the influence of a weak (on the energy scale) magnetic field on the state of dislocations and point defects in ionic crystals. It is found that complex point defects existing in a metastable state are sensitive to a magnetic field B∼1 T. The contributions are identified, and the kinetics of various types of reactions within the structural defects and between them leading to plastification of the crystals in a magnetic field are determined. The effect of light on the sensitivity of the point defects to a magnetic field is described, and the spectral characteristics of this effect are determined. A resonant effect of the combined action of a weak constant magnetic field and a high-frequency magnetic field on the dislocation mobility is found to occur when these fields satisfy the conditions of electron paramagnetic resonance. Zh. éksp. Teor. Fiz. 115, 605–623 (February 1999)     

Effect of Gd-Mn exchange on phase transitions in GdMn<Subscript>2</Subscript>O<Subscript>5</Subscript> induced by a strong magnetic field

Complex studies of the magnetic, magnetoelectric, and magnetoelastic properties of GdMn₂O₅ single crystals in strong pulsed magnetic fields are carried out in order to obtain additional indirect information on the character of the rare-earth and manganese spin ordering. It is shown that magnetic ordering of Gd³⁺ spins affects the manganese sublattice spin orientation and initiates new magnetic phase transitions. The observed magnetoelectric properties of the GdMn₂O₅ system are interpreted in terms of the theory of phase transitions.     

Collective defect formation in the high-temperature superconductor YBa2Cu3O7 under the influence of adsorbed water molecules

The mechanisms for defect formation stimulated by the adsorption of water molecules in the surface of YBa₂Cu₃O₇ ceramic are studied, together with the types of defects and their distributions. It is found that a water layer physically bound to the surface reduces the rates of annihilation and capture of positrons, changes the amount of barium and copper on the surface by a factor of two, and inhibits diffusive jumps of nickel atoms. A layer of adsorbed water excites subthreshold formation of 10²¹ cm⁻³ interstitial Ba and Cu1 atoms and transitions of oxygen from O1 to O5, and vice versa in the volume of crystallites, and the migration of defects and accumulation of Ba atoms in the surface layer, which block diffusive jumps of Ni within the volume of the crystals. These effects are related to the excitation of collective, low-frequency weakly damped motion of heavy holes in the crystal volume when defects are formed on the surface by physically adsorbed H₂O molecules, which is accompanied by Coulomb repulsion of cations from intermediate layers into interstitials and the migration of defects in the field of the collective excitations. Zh. éksp. Teor. Fiz. 116, 586–603 (August 1999)     

The nature of magnetoelastic anomalies in Nd<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> upon suppression of charge ordering by a magnetic field

This paper reports on the results of investigations into the magnetic and magnetoelastic properties of Nd_0.5Sr_0.5MnO₃ single crystals in pulsed magnetic fields up to 250 kOe, the magnetic and kinetic properties of these crystals in weak static magnetic fields, and their thermal expansion. It is demonstrated that the studied properties exhibit a number of anomalies due to a transition from the antiferromagnetic semiconducting state to the ferromagnetic metallic state upon suppression of charge ordering.     

Positron annihilation in electron irradiated Cz-Si

Defects in electron irradiated Cz-Si were studied by the positron annihilation technique. In order to know effects of the thermal history of crystals on the introduction of defects, the specimen was quenched from 1390°C to room temperature before irradiation. A clear correlation between results obtained by the positron annihilation experiments and those by infrared spectroscopy was established. From the isochronal annealing experiment, it was found that oxygen clusters were introduced by quenching treatments.     

Dislocations used to probe the defect state of an ionic crystal lattice excited by a pulsed magnetic field

This paper presents the results of an investigation into the effect of a pulsed magnetic field on the state of linear and point defects in ionic crystals. For different amplitudes (1–7 T) and pulse lengths (3×10⁻⁵ to 10² s) of the pulsed field the kinetics of the transformation of defects into a new state and their relaxation after the field is turned off are studied in the temperature range 77–400 K. It is found that the relaxation of the states of point defects is mainly through recombination, and the change of state of the dislocations and of the point defects contribute nonadditively to the change in the dislocation mobility. The exposure of the crystal to a magnetic field leads to an increase in the dislocation mobility when the sample is mechanically stressed and to a decrease in the dislocation displacement with a second field pulse. Fiz. Tverd. Tela (St. Petersburg) 39, 634–639 (April 1997)     

Magnetism in spin-coated pristine TiO2 thin films

Spin coated pristine TiO₂ thin films show magnetic behaviors that are similar to those of pulsed laser ablated TiO₂ thin films that were reported previously. It seems that in this kind of material, ferromagnetism (FM) is indeed intrinsic, and it can be achieved by various deposition techniques. The fact that oxygen annealing degrades the magnetic moment implies that the observed magnetism is likely due to defects or/and oxygen vacancies. Moreover, thick films that were deposited under the same growth conditions have the magnetic ordering degraded enormously. It is found that as for FM in undoped TiO₂ films made by the chemical solution deposition, not only do defects/oxygen vacancies play a role, but also the confinement effects seem to be important.     

Weak ferromagnetism and oxygen ordering in La2CuO4+x single crystals

The changes produced in the magnetic properties and structure of La₂CuO_4+x (0< x<0.015) single crystals by doping with oxygen are investigated by differential magnetic susceptibility and x-ray diffraction methods. It is found that the appearance of a weak ferromagnetism in weak fields H<50 Oe is accompanied by a lowering of lattice symmetry as a result of the oxygen ordering. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 159–162 (10 August 1997)     

EPR and optical properties of KYb(WO4)2 and KTb0.2Yb0.8(WO4)2 single crystals

Well oriented KYb(WO₄)₂ and KTb_0.2Yb_0.8(WO₄)₂ single crystals have been investigated for their magnetic and optical properties using the Raman and EPR techniques. The registered EPR signal is dominated by three lines ascribed to ytterbium ions: one main and two satellites. Tb ions, although non-paramagnetic, distinctly modify magnetic properties of the KYb(WO₄)₂ single crystal. Basic parameters of the spin Hamiltonian, including Zeeman and hyperfine terms (g and A matrices) as well the spatial orientation between principal and crystallographic axes systems were determined for both crystals.