The dependence of EPR linewidth on concentration in Mn/MgO single crystals

The EPR spectra of Mn/MgO single crystals grown by electrofusion have been examined at 9 GHz for manganese concentration of between 840 and 2900 ppm. The values of the spin Hamiltonian parameters deduced agreed well with those previously reported by Low (1957, 1958) and by Matarrese and Kikuchi (1956). The variation of linewidth with manganese concentration was also examined and compared with the predictions of the de Biasi and Fernandes theory of dipolar broadening in magnetically dilute systems; the peak-to-peak linewidth is concentration dependent and is of the right order of magnitude to be explained adequately in terms of this model. The results indicate that clustering, effects are absent in these Mn/MgO single crystals.     

Effect of copper impurity on the edge emission of ZnTe crystals

The results are given of studies on the edge emission of undoped and copperdoped ZnTe crystals in the temprature range 4.2–300K. The copper impurity has been found to increase the intensity of the principal edge emission band substantially. Analysis of the structure of this emission band indicated that a temprature below 160K the main role is played by the emission from excitons that are most probably bound in Cu_Zn and Li_Zn centers while at higher temperatures it is played by emission during the transition of free electrons to these centers. An appreciable role is played over the entire range of temperatures by emission from free electrons with an energy of 13 MeV. The luminescence quenching energy below 160 K has a value of 7 MeV (the binding energy of a bound exciton) and at higher temperatures it is 78 MeV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 68–73, August, 1987.     

Trapped-hole centers in MgO single crystals

The properties of the majority trapped-hole centers in MgO, such as g-factors, positions of absorption and luminescence bands, and temperatures of thermal destruction, have been analyzed with the emphasis on the observed regular trends and interrelations between the properties of these centers. Particular emphasis has been placed on the positively charged [Be]⁺ and [Ca]⁺ trapped-hole centers, which have a large cross section for recombination with conduction electrons. In these centers, a hole is localized at an oxygen ion near the impurity Be²⁺ or Ca²⁺ ion located at a regular cation site. The generation and transformation of defects due to the recombination of either relaxed conduction electrons with OH⁻-containing hole centers or cold and hot electrons with [Be]⁺ and [Ca]⁺ centers have been considered. Using the interrelation of the characteristics of hole centers and taking into account that the recombination emission band revealed at ∼6.8 eV is due to the Ca²⁺-containing centers that are stable below 50 K, the prospects for the EPR detection of the [Ca]⁺ center at T < 4.2 K have been discussed.     

Effect of cobalt impurity ions on the magnetic and electrical properties of iron monosilicide crystals

The results of experimental investigations of Fe_{1 − x} Co _x Si crystals in the impurity limit with x = 0.001, 0.005, and 0.01 are reported. The temperature and field dependences of the magnetic susceptibility have been studied. According to the experimental data, the introduction of cobalt impurity leads to a change in the energy structure, which is most pronounced in a change in the electrical properties. The temperature, field, and concentration dependences of the resistivity have been measured. The results have been interpreted in the framework of the Kondo model.     

Band-edge emission in CuI single crystals

The photoluminescence spectra of CuI single crystals have been studied at T = 4.2 K and at various excitation levels. The emission band of donor-acceptor pairs (DAP) with a maximum at about 4200 Å has been shown to possess a complex structure. Theoretical analyses and exciton spectroscopy data make it possible to calculate the ionization energies for the donors and acceptors participating in the formation of DAP, which are equal to E_D = = 0.045?0.065 eV and E_A = 0.155?0.170 eV, respectively. The fine structure of emission due to the annihilation of excitons bound on acceptor pairs (band maximum 4075 Å) has been detected and calculated. The energy of the longitudinal optical phonon participating in the exciton-phonon interaction (LO ? 18.7 meV) has been determined.     

Muon precession in iron single crystals

Changes in the muon precession signal in iron with angle of the magnetization with respect to the crystal axes are not due to intrinsic changes in hyperfine field with angle in unstrained single crystals. To confirm this with rectangular plate samples it was necessary to study methods of correcting for demagnetizing fields.     

Anisotropic emission in single crystal sputtering measurements on HCP single crystals

The ejection characteristics of single crystals of zinc, magnesium (hcp) and aluminum (fcc) were determined by bombarding various crystal surfaces with a beam of inert gas ions. The energy of the bombarding ions varied between 10 and 40 keV. The sputtered particles were collected on cooled, hemicylindrical metal collectors; with the help of an electron probe the thickness of the deposit was measured. Pronounced anisotropic emission was observed in all cases, although random emission comprises the major part of the total ejection. By comparing the 〈2023〉 ejection, which is produced by pure surface collisions, and the 〈1120〉 ejection, where focusing collisions are involved, we deduce that surface collisions are mainly responsible for the anisotropic emission. The width of both emission distributions increases linearly to the same extent in the temperature regime between 100 and 370 K. The agreement of the Mg 〈1120〉 ejection with the 〈110〉 ejection from an aluminum (111) single crystal is good and thus allows a comparison with the gold 〈110〉 ejection reported in the literature.

The assisted focusing ejection in 〈0001〉, which is very pronounced in zinc single crystals and strongly influences the 〈2023〉 ejection from the basal plane, does not show up in magnesium. No 〈111〉 ejection occurred in aluminum either. In both cases the weak repulsive potential of the low-Z atoms accounts for the lack of this preferential emission.     

Crystal orientation dependence of ferromagnetism in Fe-implanted MgO single crystals

Single crystals of MgO with (100), (110) and (111) orientations were implanted with 64 keV Fe ions at a dose of 1.9×10¹⁷ ions/cm² by using metal-vapor vacuum arc ion source (MEVVA). The magnetic properties were investigated by a superconducting quantum interference device magnetometer and Rutherford backscattering spectrometry (RBS) was used to analyze the Fe concentration and distribution. The presence of Fe nanoparticles in MgO matrix was verified by magnetization measurements. Results show that all the samples behave with ferromagnetism at 5 K and 300 K, and the coercive field, H_C, follow well the relation: at measured temperatures. The orientation dependence of the coercive field may result from the different distribution of Fe nanoparticle size.     

Magnetoelastic acoustic emission in ferrosilicon single crystals

The influence of magnetic-reversal effects on magnetoelastic acoustic emission (MAE) in single crystals of Fe + 3% Si cut in the [100], [110], and [111] directions is investigated, along with the relationship of these signals to the linear magnetostriction. It is shown that the MAE signals depend on the crystallographic directions and exhibit processes associated with rearrangement of the 90° domains throughout the entire volume of the ferromagnet.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 62–66, January, 1986.     

Epitactic formation of forsterite on MgO single crystals during vacuum annealing

Specimens of {0 0 1} MgO, prepared for analysis in the transmission electron microscope (TEM), have been heated in situ in a conventional TEM in order to study the effect of different heat treatments on the surface of the MgO specimens. A previous study, using a similar in situ heat treatment of MgO, found that at elevated temperatures (∼500 K) a film of different structure and composition formed on the surface of the sample. The previous study concluded that the composition and structure corresponded to that of MgO₂. In the present study, similar results to those shown previously have been found. However, the interpretation of these results is quite different. The films are shown to be of a composition and crystal structure that is consistent with forsterite, Mg₂SiO₄. The films can form as a result of contamination during the high-temperature in situ annealing process.     

Donor-acceptor nature of the blue self-activated emission in ZnS crystals

Optically detected magnetic resonance in ZnS shows that the blue self-activated emission is due to the recombination of an electron trapped at a donor state with a hole trapped at an A-centre acceptor state.     

FMR in surface oxidized iron single crystals

Ferromagnetic resonance absorption has been observed at room temperature in iron single crystals of whisker type (grown along [100] direction). The surface of the samples has been oxidized in air at 760 Torr at approx. 350 °C for periods up to 240 min. With the increasing degree of oxidation the resonance linewidth broadens and the resonance field shifts to lower values. Moreover, in oxidized samples an additional resonance peak situated above, the main resonance occurs, with intensity, position and linewidth depending on the period of oxidation. The ferrimagnetic resonance absorption in the iron oxide surface layer could be responsible for the occurence of this peak.     

Dimer self-organization of impurity ytterbium ions in synthetic forsterite single crystals

Paramagnetic centers formed by impurity Yb³⁺ ions in synthetic forsterite (Mg₂SiO₄) grown by the Czochralski technique are studied by X-band CW and pulsed EPR spectroscopy. These centers are single ions substituting magnesium in two different crystallographic positions denoted М1 and М2, and dimer associates formed by two Yb³⁺ ions in nearby positions М1. It is established that there is a pronounced mechanism favoring self-organization of ytterbium ions in dimer associates during the crystal growth, and the mechanism of the spin–spin coupling between ytterbium ions in the associate has predominantly a dipole–dipole character, which makes it possible to control the energy of the spin–spin interaction by changing the orientation of the external magnetic field. The structural computer simulation of cluster ytterbium centers in forsterite crystals is carried out by the method of interatomic potentials using the GULP 4.0.1 code (General Utility Lattice Program). It is established that the formation of dimer associates in the form of a chain parallel to the crystallographic axis consisting of two ytterbium ions with a magnesium vacancy between them is the most energetically favorable for ytterbium ions substituting magnesium in the position М1.     

Effect of correlation in the impurity defect distribution on the micromechanical properties of GaAs: Te single crystals

The micromechanical properties of Te-doped GaAs single crystals with free carrier density n ₀ = 10¹⁷?5 × 10¹⁸ cm^?3 were studied. The obtained data are as follows: the nonmonotonic concentration dependences of the microhardness, the lengths of dislocation rosette rays, the densities of dislocations, and the position and half-width of the Raman line of a transverse optical phonon. The data are interpreted in terms of spatial correlation in the impurity defect distribution.